Opinion Of The Scientific Committee On Consumer Safety Cyclomethicone (D4/D5) EU 1241 T Sccs O 029

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SCCS/1241/10

Scientific Committee on Consumer Safety
SCCS

OPINION ON
Cyclomethicone
Octamethylcyclotetrasiloxane (Cyclotetrasiloxane, D4)
and
Decamethylcyclopentasiloxane (Cyclopentasiloxane, D5)

The SCCS adopted this opinion at its 7th plenary meeting
of 22 June 2010

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

About the Scientific Committees
Three independent non-food Scientific Committees provide the Commission with the
scientific advice it needs when preparing policy and proposals relating to consumer safety,
public health and the environment. The Committees also draw the Commission's attention
to the new or emerging problems which may pose an actual or potential threat.
They are: the Scientific Committee on Consumer Safety (SCCS), the Scientific Committee
on Health and Environmental Risks (SCHER) and the Scientific Committee on Emerging and
Newly Identified Health Risks (SCENIHR) and are made up of external experts.
In addition, the Commission relies upon the work of the European Food Safety Authority
(EFSA), the European Medicines Evaluation Agency (EMEA), the European Centre for
Disease prevention and Control (ECDC) and the European Chemicals Agency (ECHA).
SCCS
The Committee shall provide opinions on questions concerning all types of health and safety
risks (notably chemical, biological, mechanical and other physical risks) of non-food
consumer products (for example: cosmetic products and their ingredients, toys, textiles,
clothing, personal care and household products such as detergents, etc.) and services (for
example: tattooing, artificial sun tanning, etc.).
Scientific Committee members
Jürgen Angerer, Ulrike Bernauer, Claire Chambers, Qasim Chaudhry, Gisela Degen, Gerhard
Eisenbrand, Thomas Platzek, Suresh Chandra Rastogi, Vera Rogiers, Christophe Rousselle,
Tore Sanner, Kai Savolainen, Jacqueline Van Engelen, Maria Pilar Vinardell, Rosemary
Waring, Ian R. White
Contact
European Commission
Health & Consumers
Directorate C: Public Health and Risk Assessment
Unit C7 - Risk Assessment
Office: B232
B-1049 Brussels
Sanco-Sc6-Secretariat@ec.europa.eu

ISBN 978-92-79-12742-7
ND-AQ-09-014-EN-N

The opinions of the Scientific Committees present the views of the independent scientists
who are members of the committees. They do not necessarily reflect the views of the
European Commission. The opinions are published by the European Commission in their
original language only.
http://ec.europa.eu/health/scientific_committees/consumer_safety/index_en.htm

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

ACKNOWLEDGMENTS

Prof. J. Angerer
Dr. U. Bernauer
Dr. C. Chambers
Prof. G. Degen
Dr. S.C. Rastogi
Prof. V. Rogiers
Prof. T. Sanner
Dr. J. van Engelen
Prof. R. Waring
Dr. I.R. White

(rapporteur)
(chairman)

Keywords: SCCS, scientific opinion, hair dye, cyclomethicone, D4, D5, cyclotetrasiloxane,
cyclopentasiloxane, directive 76/768/ECC, CAS 556-67-2 (D4), 541-02-6 (D5), EC 209-1367 (D4), 208-764-9 (D5)

Opinion to be cited as: SCCS (Scientific Committee on Consumer Safety), Opinion on
cyclomethicone D4/D5, 22 June 2010

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

TABLE OF CONTENTS

ACKNOWLEDGMENTS ........................................................................................... 3
1.

BACKGROUND ............................................................................................. 5

TERMS OF REFERENCE.................................................................................. 5

OPINION..................................................................................................... 6

CONCLUSION .......................................................................................... 102

MINORITY OPINION.................................................................................. 102

REFERENCES ........................................................................................... 102

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

1. BACKGROUND
Cyclomethicone (CAS 556-67-2) with the chemical name Octamethylcyclotetrasiloxane has
the following functions: antistatic, emollient, humectant, solvent, viscosity controlling and
hair conditioning in cosmetic products according to the Inventory.
Cyclomethicone is a substance classified as toxic to reproduction category 3 and according
to the cosmetic directive 2003/15/EC a safety evaluation for its use in cosmetic products is
needed.
SCCP concluded in its opinion (SCCP/0893/05) adopted during the 6th plenary meeting of
13 December 2005 that "On the basis of provided data, the SCCP is unable to assess the
risk to consumers when Octamethylcyclotetrasiloxane (D4) is used in cosmetic products.
Despite the size of the dossier submitted by industry for evaluation, it is unfortunate that
the dossier lacked meaningful information/data on actual consumer exposure to D4. The
following information is required before any further consideration:
*
*
*

Adequate information on the use of D4 in cosmetics, in particular in different cosmetic
products;
Relevant/appropriate percutaneous absorption studies at different use concentrations;
Information on the co-use, and hence consumer exposure, of related organosiloxanes,
in particular decamethylcyclopentasiloxane (D5). "

The current submission provides the data asked for by SCCP.

2. TERMS OF REFERENCE
1.

On the basis of the provided data the SCCP is asked to assess the risk to consumers
when octamethylcyclotetrasiloxane is used in cosmetic products.

Does the SCCP recommend any further restrictions with regard to its use in cosmetic
products?

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

3. OPINION
Cyclomethicone is a generic name for several cyclic dimethyl polysiloxane compounds;
according to INCI, it refers not only to octamethylcyclotetrasiloxane (D4, INCI name:
cyclotetrasiloxane), but also to cyclotrisiloxane (D3), cyclopentasiloxane (D5),
cyclohexasiloxane (D6), and cycloheptasiloxane (D7), i.e. compounds of the general formula
(CH3)2nOnSin where n = 3-7. The safety file submitted to the European Commission
concerned D4 and D5 only, therefore only these compounds D4 and D5 will be discussed in
the present opinion.
In response to the need for additional information expressed by the SCCP (SCCP/0893/05),
the applicant provided with submission III of 2006 a study report on in vitro dermal
absorption of D4 in pig skin, and a document containing a short paragraph on the co-use of
D5 and D4 as well as a summary of the toxicological database for D5. This and the
information given in the so-called “D5 White Paper of June 2005” were in some respects
considered insufficient for a new evaluation of cyclomethicone. SCCS has taken into
consideration recent evaluations on health effects of cyclomethicone compounds by the
Canadian Ministries for Environment and Health (Ref.: AR8, AR9) the Californian Office of
Environmental Health Hazard Assessment (OEHHA) (Ref.: AR10), a Cosmetic Ingredient
Review report (Ref.: AR22) and other publications retrieved from the open literature. Aside
from qualitative information on the co-use of D4 and D5, the exposure assessment is based
on concentrations of these compounds in cosmetics as given in a report by the Norwegian
Food Safety Authority (Ref.: 83) provided together with submission III.
References given in this introduction and in chapter 3.1.1 refer to the D4 references listed in
chapter 3.3.13
3.1. Chemical and Physical Specifications
3.1.1.

Chemical identity

3.1.1.1.

Primary name and/or INCI name

D4: Cyclotetrasiloxane (INCI)
D5: Cyclopentasiloxane (INCI)
Cyclomethicone (INCI)
3.1.1.2.

Chemical names

Cyclotetrasiloxane (D4)
Octamethylcyclotetrasiloxane
Cyclotetrasiloxane, octamethylCyclopentasiloxane (D5)
Decamethylcyclopentasiloxane
Cyclopentasiloxane, decamethyl-

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

3.1.1.3.

Trade names and abbreviations

Cyclomethicone (D4)
SF 1173, Miramil CM4, Tetramére D4, Silbione Tetramére D4, Cyclen D4, Oel Z020, KF 994,
Baysilone COM 10.0000, Dow Corning 244 Fluid
Cyclopentasiloxane (D5)
AEC Cyclopentasiloxane; Botanisil CP-33; Dow Corning 245 Fluid; KF995; Mirasil CM 5; SF
1202; Wacker-Belsil CM 040
3.1.1.4.

CAS:
EC:
3.1.1.5.

CAS / EC number
D4
556-67-2
209-136-7
Structural formula

Cyclotetrasiloxane (D4):
Cyclopentasiloxane (D5):
3.1.1.6.

D5
541-02-6
208-764-9

n=4
n=5

Empirical formula
D4

Formula:

C8H24O4Si4

C10H30O5Si5

3.1.2.

Physical form

Clear, colourless liquids
3.1.3.

Molecular weight

Molecular weight:
3.1.4.

296.2

370.8

Purity, composition and substance codes

D4
Purity of octamethylcyclotetrasiloxane used in tests is described as unknown or >95%
(maximum 99.8%).
Purity of the typical octamethyltetracyclosiloxane used in the formulation of cosmetic
products is not reported.
D5
7

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

According to the applicant, the tests used relatively pure samples of D5 (97% - > 99%)
with pivotal studies conducted using the same batch of D5 (BxWCO 15338, > 99% pure).
3.1.5.

Impurities / accompanying contaminants

D4
Maximum 5% decamethylcyclopentasiloxane (D5) and maximum 1% hexamethylcyclotrisiloxane (D3)
According to PCPC (former CTFA), up to 1% impurity of homologues with 3, 5, 6 or 7 silicon
atoms can be present.
D5
No specific data submitted.
3.1.6.

Solubility
D4

Water:
3.1.7.

Log Pow:
3.1.8.

20µg/L at 25°C

17-20 µg/L

Partition coefficient (Log Pow)
D4

5.1

5.2

Additional physical and chemical specifications
D4

Melting point:
Boiling point:
Flash point:
Vapour pressure:
Density:
Viscosity:
pKa:
Refractive index:
Surface tension:

17.5°C
175°C
/
0.681 torr at 20°C
0.95
/
/
/
/

D4
Conversion factor:

1 ppm = 12 mg/m3; 1 mg/m3 = 0.0835 ppm

D5
Conversion factor:

1 ppm = 15.1 mg/m3; 1 mg/m3 = 0.0645 ppm

3.1.9.

Homogeneity and Stability

No data submitted

- 44.2 °C
211.0 °C
/
0.148 torr at 23 °C
0.96
3.87 cst
/
/
18.5 dyne/cm at 25 °C

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

3.2.

Function and uses

The functions of octamethyltetracyclosiloxane in cosmetics are reported as antistatic /
emollient / humectant / solvent / viscosity controlling / hair conditioning. In addition,
silicone containing formulations have a good spreadability.
Ref.: AR 1
Depending on the product type, the concentration of D4 in formulations varies between 0.1and 54%. It is common to use a blend of cyclosiloxanes D4, D5 and D6 in cosmetic
products. Thus, products containing D4 may also contain D5 and D6.
Ref.: AR 6
Cyclosiloxane blends containing D4, D5 and D6 are used in the formulation of various types
of hair care and skin care products as well as in antiperspirants/deodorants.
Ref.: 1
Cyclic siloxanes, including cyclomethicone, are used as precursors in the production of
polydimethylsiloxane, which are widely used in various industrial and consumer
applications, topical pharmaceutical formulations and as breast implants. The polymers
contain some residual monomers.
Certain food products are processed using silicone antifoam containing octamethyltetracyclosiloxane.
Ref.: AR2, AR 6
D5 can be used instead of D4 in cosmetic/personal care formulations. However, due to the
differences in physical properties and in the sensory characteristics, the level of D5 in most
cases needs to be adjusted in order to maintain comparable functional properties of the
formulation. Some formulations can use a combination of D4/D5 but the combined level
generally will not exceed the level that would be used if just one of the materials was used.
In practice, however, manufacturers use D4 or D5 rather than blends.
Ref.: 81
Toxicological Evaluation
The toxicological evaluation of the cyclomethicone compounds D4 and D5 is presented in
two separate sections, each one giving the relevant references. The opinion then provides a
synopsis comparing the known toxicities, and an exposure assessment for these ingredients
(section 3.6). Because of the co-use of D4 and D5 the safety evaluation for cyclomethicone
covers both compounds.

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

3.3.

Toxicological Evaluation of D4 (Octamethylcyclotetrasiloxane;
Cyclotetrasiloxane)

3.3.1.

Acute toxicity

3.3.1.1.

Acute oral toxicity

Acute oral toxicity information is based on summary information, no study reports were
provided. The available information indicates that the substance possesses low acute oral
toxicity. None of the studies are acceptable by modern standards. The table below
summarises the information from the IUCLID data set.
Table 1: acute oral toxicity
Year
1956

1961

Species
Rat

Rat

Number
2

Sex

Dose
2000 mg/kg bw

Vehicle
corn oil

2000 mg/kg bw

corn oil

> 4600 mg/kg
bw
5.0 ml/kg bw by
gavage (>4800
mg/kg bw)

1974

Rat

1979

Rat
(Wistar)

male

none

Results
No mortality; initial weight
loss; slight to moderate liver
pathology. LD50> 2000
mg/kg bw
no mortality; slight
diarrhoea and diuresis Day
2; slight liver and kidney
injury
no mortalities
no mortality, no clinical
signs
LD50 >5.0 ml/kg bw

Ref.: AR7
3.3.1.2.

Acute dermal toxicity

Table 2: acute dermal toxicity
Year
1984

Species
Rat
(Wistar)

Number
5 per sex

Sex
male/
female

Dose
2.5 ml/kg
(>2400 mg/kg)
bw

1974

Rabbit

1979

Rabbit
(New
Zealand
White)

male/
female

> 4640 mg/kg
bw
> 10000 mg/kg
bw

Purity
commercial
product;
purity
unspecified
/
commercial
product;
purity
unspecified

Results
No mortalities

No mortalities
No mortalities;
ataxia; hyperactivity;
decreased activity;
eschar formation:
burned areas on back

Ref.: AR7
3.3.1.3.

Acute inhalation toxicity

Guideline:
Species/strain:
Group size:
Test substance:
Purity:
Batch no:
Dose:

OECD 403 "Acute Inhalation Toxicity", 1981
Rat (Fischer 344)
5 males and 5 females
Octamethylcyclotetrasiloxane
96%
LL 107568
20.12, 32.82 and 57.69 mg/l air
(or 1680, 2740 and 4817 ppm)

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

Vehicle:
Exposure:
GLP:

none
4h
in compliance

The study was indicated to have followed OECD 403 "Acute Inhalation Toxicity", 1981, but
there was no control group. No reason for this omission was given. The impurities were
given as 4% decamethylcyclopentasiloxane and 0.1% hexamethylcyclotrisiloxane.
Exposure was nose–only to mixed test atmospheres of vapour and liquid phase (aerosol) for
4 h. The particle size of the aerosol was not given.
Results
Mortality: 0 % at 20.12 mg/l; 30 % (1 male, 2 female after 3 days) at 30.03 mg/l; 90 % at
54.37 mg/l (4 male, 5 female during or shortly after exposure).
There was an initial weight loss and reduced food consumption in all groups. Hunched
posture, stiff gait, ruffled fur in all groups; restlessness and/or excitement during exposure
in all animals was observed but did not seem to be dose related. These symptoms were
resolved in most cases by Day 6. Rales and/or head drop was noted in some low and mid
dose males for 1-3 days. Tachypnea was seen towards the end of the exposure period in
both mid dose males and females and the surviving high dose male. A low dose female had
a red nasal discharge.
Postmortem analysis of the animals that died during the study and at the end of the study
showed red discoloration of the lungs. In the premature deaths there were also reddish foci
in some tissues, notably the mandibular lymph node and thymus. These were considered
incidental by the study authors.
The study authors noted a trend in increased lung and spleen weight in both sexes and a
decrease in thymus weight in males only. These were discounted as there was not adequate
data.
The LC50 was calculated to be 36 mg/l (corresponding to approx. 2,975 ppm).
Ref.: 3
Table 3: other (non- GLP) acute inhalation studies, indicated in IUCLID data set
Year
1956

Species
Rat

Number
3

Sex

1961

Rat

1974
1984

Rat
Rat
(Wistar)

5 per sex

male/
female

Exposure time
7h

7 h saturated
atmosphere at bath
temperature 100 °C
1h
4 h acute head–
nose aerosol
exposure ;
commercial product

Dose
saturated
atmosphere at
bath temp. 23
and 100 °C ~ 200
and 1000 ppm

Results
No mortality; very slight
initial weight loss;
moderate liver
pathology.
No mortality; no clinical
signs; no gross necropsy
findings.

> 17.6 mg/l
12 mg/l (~ 1000
ppm)

LC50 > 12 mg/l
Mortality: 0/10, non–
specific signs on the
exposure day.

Ref.: AR7
3.3.2

Irritation and corrosivity

3.3.2.1.

Skin irritation

Two non-GLP studies are included in the IUCLID Dataset.
The first study was performed in rabbit in 1978. The test material (octamethyltetracyclosiloxane) was slightly irritating. No further information is available.

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

The second study was performed in 1979 by 24h exposure (semi-occlusive) of ears of 2
New Zealand rabbits to 500 µl neat octamethyltetracyclosiloxane (commercial product,
purity not specified). The test material was not irritating (observation period of 7 days). No
further details are available.
Ref.: 16
3.3.2.2.

Mucous membrane irritation

No study report on eye irritation was provided with the dossier. One study summary was
included in Submission 1
Draize test
Guideline:
Animals:
Test material:
Dose:
Vehicle:

/
One male and one female New Zealand White rabbit, 3-4 kg bw
Octamethyltetracyclosiloxane, purity unknown
100 µl, undiluted
/

100 µl neat octamethyltetracyclosiloxane was instilled into the conjunctival sac of one eye of
each of the two rabbits and the lids were gently held together for about one second. The
eyes were not rinsed after treatment. The other eye served as control. Eyes were examined
at 1, 24, 48, 72 h and 7 days after application.
Results
Apart from hyperaemic vessels in the conjunctivae of one rabbit eye at one hour after
application, which were resolved by 24 h, no signs of irritation were observed.
Ref.: 16
Comment
In addition, 5 other studies performed in 1956-1961, are listed in the IUCLID Dataset. The
studies did not comply with GLP, and only very little information on test material, dose, etc.
is available. A slight conjunctival irritation, with no corneal injury, observed in one study,
was resolved within 24 h.
3.3.3.

Skin sensitisation

Magnusson-Kligman maximization test
Guideline:
Species/strain:
Group size:
Test substance:
Purity:
Batch no:
Dose levels:
Observation:
GLP:

EU Method B.6 Skin senzitisation
Albino guinea pigs (Bor:DHPW)
20 test and 10 control (positive and negative)
D4 (Baysilone COM 100000)
> 99%
/
Induction: 1% intracutaneous and 100% epicutaneous
Challenge: undiluted and 10 % in paraffin oil
24 and 48 hours p.a.
in compliance

Sensitisation was tested in 20 female guinea pigs which had been pretreated with 1% D4 in
vehicle (paraffin oil) including Freund's complete adjuvant by intracutaneous injections and
closed dermal topical application of undiluted test compound for 48 h on the shaved neck
and back area. Challenge reaction with undiluted and with 10% test substance in paraffin oil
were induced by occluded patch test on day 14 after the last exposure. No skin reactions
(reading at 24 and 48 hours) were observed.

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

Results
D4 produced no skin hypersensitivity response.
Ref.: 17
3.3.4.

Dermal / percutaneous absorption

In vitro absorption through human skin
Guideline:
Tissue:

/
Dermatomed abdominal epidermis, from 6 human cadaver skin (5 males
54-75 years and one female 49 years).
Method:
Bronaugh* Flow-Through Diffusion Cells, skin area available for diffusion
0.64 cm2
14
Test substance: C-octamethyltetracyclosiloxane (Lot No. 921217, radiochemical purity
98.71%, specific activity 2.0 mCi/mmol) diluted with unlabelled
octamethyltetracyclosiloxane (Lot No. LL084732, purity 99.8%).
Specific activity of test material: 1.1 µCi/mg.
Specific activity of test material formulated in an antiperspirant: 0.51
µCi/mg and 0.79 µCi/mg, in two separate experiments.
The antiperspirant was homogenous with respect to content of the test
material at a concentration of 62 % (W/W)
Dose levels:
Target dose level: 8 mg/cm2, Actual dose levels: 7.0-19.5 mg/cm2 and
specific activity 4.5-13.8 µCi per piece of skin
Replicate cells: Duplicate experiments were performed using skin from all donors, both for
the absorption of neat 14C-octamethyltetracyclosiloxane and the formulated
antiperspirant.
GLP:
Statement of compliance
The skin penetration of neat 14C-octamethyltetracyclosiloxane and 14C-octamethyltetracyclosiloxane formulated in an antiperspirant was evaluated using dermatomed human epidermis
mounted on a flow-through diffusion cell system, and Hank’s balanced salt solution as
receptor fluid.
Two dermatomed skin samples per donor were used. Their barrier integrity was checked by
percent absorption of the applied dose of 3H-H2O during 20 min.
The test materials were delivered by the use of microsyringes, and the delivered amount
was determined gravimetrically. Immediately after dosing, charcoal baskets were placed
above the skin and secured into a custom designed cap to capture any volatilised material.
At the end of 24 hours, the charcoal baskets were removed and extracted, skin was washed
and solubilised. The receptor fluid was collected at 1h, 2 h, 3 h, 4 h, 5 h, 6 h, 9 h, 12 h, 15
h, 18 h, 21 h and 24 h. The radioactivity in each sample was measured by scintillation
counting.
Results
The data from all experiments with neat 14C-octamethyltetracyclosiloxane could be used.
However, data from two of the six experiments for the absorption of 14C-octamethyltetracyclosiloxane-antiperspirant were eliminated (the barrier integrity of skin from one donor
did not conform to the predefined parameters, and there was not enough test material for
the experiments in the second case). The average recovery of the test material from the
experiments with the neat 14C-octamethyltetracyclosiloxane was 91.6±8.4% (79.3100.7%), and that from experiments with the neat 14C-octamethyltetracyclosiloxaneantiperspirant was 103.8±3.84% (100.5-108.7%). Most of the test material was evaporated
from the skin surface and that was trapped in the charcoal baskets: 88.2±8.5% (76.397.4%) for the experiments with neat 14C-octamethyltetracyclosiloxane and 100.4±3.6%
(96.1-104.0%) for the experiments with 14C-octamethyltetracyclosiloxane-anti-perspirant.
The average cumulative percutaneous absorption (skin + receptor fluid) of
13

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

octamethyltetracyclosiloxane in the experiments with neat 14C-octamethyltetracyclosiloxane
was 0.47 ± 0.07% (0.337-0.789%) and that in the experiments with the 14Coctamethyltetracyclosiloxane-antiperspirant was 0.45 ± 0.18% (0.153-0.939%).
Ref.: 19
Comments
Amounts of test material applied on the membranes are not described, but it may be 7-19
mg/ cm2. The average absorption of octamethyltetracyclosiloxane from formulated
antiperspirant represents experiments performed with the use of skin from 4 donors only.
The maximal dermal absorption of octamethyltetracyclosiloxane observed in this study is
0.94 % of the applied dose.
From submission III:
In vitro dermal absorption of D4 through pig skin
Guideline:
Date of test:
Test system:

Draft OECD 428 (1994)
Nov 2006
Yucatan miniature pig dermatomed (320-500 µm) skin on a flow-through
diffusion cell, equipped with charcoal basket
N° of samples: 18 samples per formulation and D4 test concentration, originating from 3
miniature pigs
Test substance: 14C-octamethyltetracyclosiloxane (Lot No. 921217, radiochemical purity
98.71%, specific activity 2.0 mCi/mmol) diluted with unlabelled
octamethyl-tetracyclosiloxane (Lot No. LL084732, purity 99.8%).
Specific activity of the test material formulated in antiperspirant, skin
moisturizer or cuticle coat at two different concentrations was 1.0 – 1.2
mCi/g
Formulations:
Skin moisturizer
5.0% and 41.7% D4
Roll-on antiperspirant 10.6% and 62.2% D4
Cuticle coat
51.6% and 95.8% D4
(exact compositions not stated)
Sampling times For skin moisturizer:
1, 2, 3, 4, 5, 6, 9, 12, 12, 15, 18, 21, 24 hours
For antiperspirant and cuticle coat:
1, 2, 3, 4, 5, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24 hours
Receptor fluid: physiological buffer, Hank’s Balanced Salt Solution with 0.6% HEPES,
0.005% gentamicin and 4% bovine serum albumin, pH 7.3-7.4
Applied amount: 10 mg D4 per cm2 of pig skin
Exposure time: 24 h
GLP/QAU:
in compliance
Three formulations (skin moisturizer, antiperspirant and cuticle coat), containing 14C-labeled
cyclomethicone at two different concentrations, were applied to dermatomed miniature pig
skin membranes. Each dosing formulation was applied at the targeted dose of 10 mg/cm²
to skin samples prepared from three pigs that were assessed in six replicates (generating
18 samples per test formulation and D4-concentration).
The barrier integrity of each piece of skin was evaluated prior to dosing by measuring
penetration of tritiated water. In case the results were unsatisfactory, the concerned skin
samples were not further used.
The solubility of the test article in the receptor fluid was tested in a preliminary assay and
showed to be 4 ppm, which is considered 10 times higher than the expected percentages to
be measured after skin penetration at the different time points.
Physiological receptor fluid was pumped in the compartment beneath the skin samples and
collected at predetermined time points over a period of 24 hours. Immediately after dosing,
14

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

a charcoal basket was placed in each diffusion cell above the skin exposure site to capture
any volatilized material. At the end of the 24h exposure period, charcoal baskets were
removed and the application site was gently blotted using dry swabs and cotton-tipped
applicators moistened with 1% aqueous soap solution. The skin was then tape-stripped and
solubilized.
Radioactivity was measured in each sample by liquid scintillation analysis. Percent dose
absorbed was calculated from the radioactivity recovered from the skin samples after
washing and tape stripping, and receptor fluid samples collected over 24 hours
Results
The percentages of doses ± standard deviations were the following:
5% D4

41.7% D4

10.6% D4

62.2% D4

51.6% D4

95.8% D4

moisturizer
(n=17)

antipersp.
(n=14)

antipersp.
(n=16)

cuticle coat
(n=15)

Skin surface:
- skin washes
- tape strips
- diffusion cell wash

0.24
± 0.01

0.23
± 0.03

0.42
± 0.04

0.32
± 0.03

0.24
± 0.01

0.25
± 0.02

Volatilized:
- charcoal basket

90.90
± 1.42

90.27
± 1.30

98.57
± 0.80

94.85
± 0.88

98.18
± 0.84

105.13
± 0.38

Skin
(after tape stripping)

0.01
± 0.00

0.004
± 0.001

0.01
± 0.01

0.03
± 0.01

0.05
± 0.01

Receptor fluid

0.01
± 0.01

0.01
± 0.00

0.000
± 0.000

0.01
± 0.00

0.01
± 0.01

0.004
± 0.001

Dose recovery

91.16
± 1.43

90.52
± 1.32

99.00
± 0.83

95.18
± 0.90

98.46
± 0.84

105.44
± 0.36

Dermal absorption
(skin + receptor fluid)

0.02
± 0.01

0.02
± 0.00

0.004
± 0.001

0.02
± 0.01

0.04
± 0.01

0.05
± 0.01

Measurement

Regardless of the D4-formulation used and the concentration of the ingredient, the majority
of the applied amount volatilized from the skin surface and was captured in the charcoal
baskets placed above the exposure site (> 90% of the applied dose). A small amount of the
applied dose (< 0.5%) was found on the skin surface after 24 hours of exposure. Total
percent dose absorbed in pig skin and receptor fluid was estimated to be ≤ 0.05% of the
applied dose in all experiments. Only ≤ 0.01% of the applied 14C-D4 penetrated through the
skin into the receptor fluid with the mean cumulative penetration over 24 hours being less
than 0.6 µg equivalents D4/cm² of skin regardless of formulation and concentration used.
The permeability coefficient (Kp) was estimated to be 10-7 cm/h (skin moisturizer, 5% D4)
and 1.9*10-9 cm/h (antiperspirant, 10.6% D4).
Conclusion
Based upon the presented data, the in vitro dermal absorption of 14C-D4 shows to be
maximum 0.05% (or 0.6 µg/cm²) in the three formulations and different concentrations
tested.
Ref.: 80

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

In vivo
Percutaneous absorption of

C-octamethyltetracyclosiloxane in the rat

Guideline:
/
Species/strain: Rat, CDF®(Fischer 344)/CrlBR
Sex and age:
Female, 10-11 weeks old
Test groups, number of animals and weight:
Phase 1 (high dose)
Group 1 (control, mass balance), 2 animals
Group 2 (mass balance), 16 animals
Group 3 (control, blood kinetics)/cannulated (24 hours), 2 animals
Group 4 (blood kinetics)/cannulated (24 h), 8 animals
Phase 2 (medium dose)
Group 5 (control, mass balance), 2 animals
Group 6 (mass balance), 16 animals
Group 7 (reserve), 2 animals
Phase 3 (low dose)
Group 9 (control, mass balance), 2 animals
Group 10 (mass balance), 16 animals
Group 11 (reserve), 2 animals
Cannulated animals weighed 138-155 g, others were of 122-136 g
14

C-octamethyltetracyclosiloxane, Lot 990316, radiochemical purity
99.56%, specific activity 26.62 mCi/m mol (69.7 mCi/g). Unlabeled D4, Lot
LLO24S10, purity 99.62%. Combined 14C-D4 and D4 of specific activity
33.2 mCi/g (Ref. # 990316D) was used as test substance.
Dose levels:
Phase 1: 10.0 mg/cm2, test material with specific activity 1.59 mCi/g
Phase 2: 4.8 mg/cm2, test material with specific activity 3.52 mCi/g
Phase 3: 2.0 mg/cm2, test material with specific activity 7.9 mCi/g
The animals in cannulated (blood kinetics) group (Group 3) were exposed
with 10 mg/cm2 of 14C-octamethyltetracyclosiloxane. Animals in control
groups were not dosed
Vehicle:
no vehicle, the 14C-octamethyltetracyclosiloxane was diluted with D4
Exposed area: 2.5 cm²
Exposure time: Individual subgroups of 4 animals in each mass balance group were
exposed for 1h, 6h and 24 h. An additional subgroup of 4 animals (Wash
Group) within each group was exposed for 24 h to evaluate disposition of
the absorbed test material up to 168 hour. The skin of the animals in these
last subgroups was washed after 24 h. Cannulated animals were exposed
for 10 h
GLP:
Statement of compliance

Test substance:

The percutaneous absorption of 14C-octamethyltetracyclosiloxane was investigated in female
Fischer 344 rats after topical application of 10, 4.8, and 2 mg/cm2 (target values). The rats
were exposed in a semi-occluded manner using an aluminium skin depot with charcoal
basket for collection of volatilised test article. The rats were housed in Roth-style
metabolism cages to enable the collection of urine, faeces and exhaled air. At the
termination of the exposure or at 168 h post exposure, blood was collected via cardiac
puncture; the charcoal baskets were removed and extracted; skin was washed, tape
stripped, excised and solubilised in 35% tetraethylammonium hydroxide (TEAH). Remaining
carcasses were also solubilised in TEAH. Radioactivity content in each sample was measured
by liquid scintillation counting. The percent dose absorbed was determined as the amount of
16

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Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

radioactivity in expired volatiles, carcasses, excreta, skin and cage rinses. More than 90% of
14
C-octamethyltetracyclosiloxane was evaporated from the skin surface within 1 h in all
experiments. (Except in phase 1, ca. 66% test material was evaporated in 1 h and more
than 90% within 6 hour. However, the radioactivity recovery in this subgroup was only
76%) The recovery of test materials in all experiments (except phase 1, 1 h exposure) was
91.7±1.7% - 101.88±5.9%.
The absorption time course pattern was the same at all dose levels: significant decrease in
percent dose absorbed over time, with absorption after 24h significantly lower than
absorbed at 1h while absorption at 6 h was not different from either. The percent of
absorption did not differ across the groups compared by dose levels (p>0.05) at any given
time (1, 6 or 24 h exposure). However, 14C-octamethyltetracyclosiloxane absorption
(±standard error of the mean) in the Wash Group after 168 h (0.350±0.009%,
0.467±0.014% and 0.513±0.084% respectively for high, medium and low dose) was
significantly lower (p<0.01) than that seen after 24 h exposure (0.609±0.086%,
0.567±0.053% and 0.756±0.081% respectively). The study author consider that the
absorbed test material remaining in 24 h may migrate to the skin surface and continue to
evaporate.
In addition, the highest dose of the neat 14C-octamethyltetracyclosiloxane (10 mg/cm2) was
applied dermally to six jugular vein cannulated animals, and blood samples were collected
up to 10 h after exposure. The samples were extracted and analysed by liquid scintillation
counting
and
gas
chromatography-mass
spectrometry.
Concentrations
of
octamethyltetracyclosiloxane in all blood samples were not different from the background
(controls).
Ref.: 18; AR11
Human dermal absorption of 13C-octamethyltetracyclosiloxane
Dermal absorption of 13C-octamethyltetracyclosiloxane in 6 human volunteers (3 males and
3 females) was investigated by the application of 1.4 g (for males) and 1 g (for females), in
a divided dose to each axilla. Blood and exhaled air samples were obtained prior to
exposure and at 1, 2, 4, 6 and 24 after application. 13C-octamethyltetracyclosiloxane levels
were significantly elevated above baseline in blood and plasma at 1, 2, 4 and 6 h and in
exhaled
air
at
all
time
points
after
exposure.
The
peak
levels
of
octamethyltetracyclosiloxane in the blood (4.45±1.10 ng/g for females and 1.30±0.77 ng/g
for males) were found at 1 h and dropped at subsequent time points. The
octamethyltetracyclosiloxane levels in exhaled air were also increased after application in all
individuals and the highest levels were found at 1 hr. The mean peak
octamethyltetracyclosiloxane level in exhaled air was 111±113 ng/L for females and 30 ±
37 ng/l for males. The exhaled air levels of octamethyltetracyclosiloxane generally reflected
blood samples but the correlation was poor (r = 0.764).
Ref.: 21
Comments
The study does not comply to GLP. The variations in the octamethyltetracyclosiloxane levels
in blood and exhaled air among the individuals may be due to non-standardised method of
application and also to different individual percutaneous absorption rate.
Percutaneous absorption studies of octamethyltetracyclosiloxane (D4) using the
human skin/nude mouse model
Guideline:
Species/strain:
Human skin:

/
Female BALB/C nude mice weighing 25-30 g, N = 7
Human foetal forearm skin from aborted foetuses (16-22 weeks)
17

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

Test substance:
Dose levels:
Vehicle:
Exposed area:
Exposure time:
GLP:

C-octamethyltetracyclosiloxane, Lot No. 9711210, radiochemical
purity 98.9%, specific activity 49.39 mCi/m mol
15.7 mg/cm2, 10 µl
no vehicle, neat 14C-octamethyltetracyclosiloxane was used
Skin grafts of approximately 25 mm in diameter
24 h
/

The percutaneous absorption of neat 14C-octamethyltetracyclosiloxane in human skin using
the human skin/nude mouse model was evaluated. The distribution of the percutaneously
absorbed test material in dermis, epidermis and adipose tissue of the skin was also
investigated.
Human skin was grafted (10-20 mm in diameter) onto nude mice. Before starting the
percutaneous absorption experiment, animals were kept for 2-4 months to allow graft
healing and growth to approximately 25 mm in diameter. The skin grafts were exposed with
14
C-octamethyltetracyclosiloxane (15.7 mg/cm2, 10 µL) by the application of an aluminium
skin depot with charcoal basket for the collection of volatilised test article. After 24 h, skin
depots were removed from the animals and application areas were tape stripped. The
charcoal baskets were separated for the determination of trapped test material. The animals
were returned immediately to their metabolism cages for an additional 48 h. Urine, faeces
and KOH traps were collected every 24 hours. At the end of 72 h, the human skin graft,
mouse skin, carcass, cage washes, and charcoal tube and KOH solutions from bubblers were
collected. The radioactivity in all samples, after dissolving/extracting in suitable solvents
was measured by liquid scintillation counting.
A similar study with additional 4 animals was performed for the investigation of distribution
of the penetrated test material in dermis, epidermis and the skin adipose tissue. After 24
hour exposure, the graft was cut, and the application site was separated. Adipose tissue
was cut with a scalpel; and dermis was separated from epidermis under a dissecting
microscope.
Results
The recovery of the applied dose in the percutaneous absorption experiments was
96.4±12.8% (81.2-119.4%). Most of the applied radioactivity dose was recovered in the
charcoal baskets (evaporation from the application site: 94.6 ± 12.3 % (80.1-117.0%). The
percutaneously absorbed radioactivity of the applied dose was 1.09 ± 0.46% (0.77-1.94%)
as: 0.01 % (application site) + 0.54% (excreta) + 0.46% (charcoal volatile trap) + 0.05%
CO2 trap + 0.02 carcass. The mean distribution of the total radioactivity recovered in the
skin was 61% in the epidermis, 29% in the dermis and 10% in the adipose tissue. The
absolute amount of 14C-octamethyltetracyclosiloxane in the adipose tissue of the four
animals was 75±76 ng (0 - 156.7 ng).
Ref.: 20; AR 12
Comments
The study is not relevant for the calculation of the MoS.
General comment on dermal absorption
There is some variation in results of in vitro and in vivo studies with D4. In vitro an average
of 0.5% of octamethyltetracyclosiloxane (D4, applied neat or in antiperspirant formulation
containing 62% (w/w) D4 was absorbed in human cadaver skin and the receptor fluid after
24 h of exposure, with dermal absorption of 0.94% of the applied dose as an upper value
(Ref. 19). Lower values were found in an in vitro study with pig skin, where dermal
absorption of 14C-D4 was maximum 0.05% in the three formulations and different
concentrations tested (Ref. 80). Similar to in vitro studies with human or pig skin, also the
in vivo rat study demonstrated that the majority (~90%) of D4 applied volatilized from the
skin surface before being absorbed. On average less than 1.0% of applied D4 appeared to
18

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

be absorbed in vivo, with the majority remaining in the skin. Consistent with in vitro results
for human cadaver skin, pharmacokinetic modelling of dermal absorption in human
volunteers (Ref. AR13) indicated that 0.12% and 0.30% of applied D4 was absorbed into
systemic circulation for men and women, respectively.
A value of 0.5% for dermal absorption of D4 is taken for the safety assessment of D4.
3.3.5.

Repeated dose toxicity

3.3.5.1.

Repeated Dose oral toxicity

14-day
Guideline:
Species/strain:
Group size:
Test substance:
Batch:
Purity:
Dose levels:
Vehicle:
GLP:

/
Rats, Sprague Dawley
8 per dose/sex
D4
Technical grade D4 lot LL108831
>98% (HPLC)
0, 25, 100, 400 and 1600 mg/kg/day D4. Control vehicle only
Methocel A4M 0.5% w/v and distilled water
in compliance

The animals were dosed by gavage for 5 days/week for 2 weeks. The animals were checked
daily for clinical signs. Body weights were recorded on study day -1, day 7 and at term.
Post-mortems of all animals were conducted. The liver was weighed and examined for gross
pathological change. Other tissues were preserved for possible future histopathology.
There were no mortalities due to the test substance but 2 high dose females died due to
gavage errors. At post-mortem, 5 others showed trauma as a result of gavage errors.
Results
No overt signs of toxicity were observed. Significantly decreased body weight at 1600
mg/kg was recorded. Liver weights increased at 100 and significantly at 400 and
1600 mg/kg bw/day in both sexes. At 25 mg/kg bw/day, the liver weight increase was
slight, but in males the relative liver weight increase was significantly different from
controls.
Ref.: 4
Guideline:
Species/strain:
Group size:
Test substance:
Batch:
Purity:
Dose levels:
Vehicle:
GLP:

/
Rabbit, New Zealand White
6 female per dose
D4
AJ844
99.8%
0, 500 and 1000 mg/kg/day D4. Control vehicles only
Methocel 0.5% w/v in distilled water
in compliance

The animals were dosed by gavage daily for 2 weeks. The animals were checked daily for
clinical signs. Body weights were recorded on study day -1, day 7 and at term.
Post-mortems of all animals were conducted. The liver was weighed and examined for gross
pathological change. Other tissues were preserved for possible future histopathology.
Results
There were no mortalities due to the test substance but 1 low dose female died due to
gavage errors.
19

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

No overt signs of toxicity were observed. There was a significant decrease in body weight at
both dose levels. The thymus showed a marked decrease in size in most animals and a
decrease in the spleen in some animals at both dose levels. Mesenteric lymph nodes were
smaller at the low dose in some animals. Changes in the liver included accentuated lobular
pattern, pale areas and increased fragility in some animals at 1000 mg/kg bw/day. These
changes were attributed to marked reductions in food intakes and body weights.
D4 administered rabbits at 500 and 1000 mg/kg bw/day produced marked reductions in
food intakes and body weights.
Ref.: 6
28-day
Guideline:
Species/strain:
Group size:
Test substance:
Batch:
Purity:
Dose levels:
Encapsulation:
GLP:

/
Rat, Sprague Dawley young and adult
5 per dose/sex/age group
microencapsulated D4 in diet
Dow Corning 244 Fluid
/
2.1% D4 in basal diet. Control basal diet only
modified cornstarch or gelatine
/

This was a 28-day feasibility feeding study using Dow Corning 244 Fluid encapsulated in
diet. The encapsulation traps the liquid droplet of D4 in a capsule of 80–90% gelatine, 5%
modified cornstarch and 15% sucrose.
The study had 4 groups: young (male 180g; female 138g) and adult (male 306; female
245g) animals and their respective controls.
The animals were checked daily for clinical signs. Body weights were recorded every fourth
day. The estimated intakes of D4 for young and old male and female rats were approx. 200300 mg/kg/day. No dietary analyses were performed. Therefore, actual intake of D4 was
not determined.
Results
No deaths were recorded. In both treated age groups, there were signs of stress (rough fur
and emaciation). Food consumption was reduced with consequent reduced body weight
gains. At post-mortem this was seen as depleted body fat reserves in all treated animals.
The caecal contents were watery. No histopathology was performed.
Ref.: 5
Comment
The value of this study is limited since there are scant details of dose achieved and gross
post-mortem of organs.
3.3.5.1.2

Repeated Dose (28 days) dermal toxicity

Guideline:
Species/strain:
Group size:
Test substance:
Batch:
Purity:
Dose levels:

/
Rabbit, New Zealand White
5 per dose/sex
Baysilone COM 10000 undiluted
99.8%
0.1, 0.3 and 1.0 ml/kg D4 (equivalent to 96, 190 and 960 mg/kg bw)
20

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

Controls were untreated.
1.0 ml/kg groups maintained for a 2 weeks recovery period.
in compliance

Recovery:
GLP:

This was a 3-week dermal toxicity study (5 days/week) followed by a two week recovery
period. Neat D4 was applied to shaved dorsum. The animals were checked daily for clinical
signs. Body weights were recorded on study day -1, day 7 and at term.
Clinical signs were observed at least twice daily. Skin changes scored after Draize.
Haematology and blood chemistry were examined prior to termination. Post-mortems were
performed on all animals and major organs weighed. Histology of the control and high dose
group was carried out.
Results
There were no clinical signs of toxicity. There were no effects on survival, body weight gain,
food consumption, haematology, clinical chemistry, urinalysis, macro and micro pathology.
A No Observed Effect Level (NOEL) of 1 ml/kg (equivalent to 960 mg/kg body weight) was
established for this study.
Ref.: 7
3.3.5.1.3

Repeated Dose inhalation toxicity

14-day
Guideline:
Species/strain:
Group size:
Test substance:
Purity:
Batch:
Dose levels:
Vehicle:
Exposure:
GLP:

/
Rat (Charles River CD)
5 males and 5 females
Technical grade Dow Corning 244 fluid Octamethylcyclotetrasiloxane)
~ 98%
Technical grade D4, lot 107568
0, 100, 200 and 400 ppm (0, 1.2, 2.4, 4.8 mg/l)
air at 22 ±20C and 30-70% relative humidity
6 h whole body inhalation
in compliance

This was a 14-day whole body inhalation range-finding study. Dosing was for 6h/day for 14
consecutive days. D4 vapour was diluted as necessary with air.
The animals were checked daily for clinical signs. Body weights and food consumption were
recorded every fourth day.
Results
No deaths or treatment-related signs were noted during the study. There were no effects on
body weight gain. A slightly lower food intake was noted in females at 400 ppm in week 1.
Food intake was further reduced in the second week of the study. No clinical pathology or
necropsy was performed.
Male and female rats tolerated exposure levels up to 400 ppm for two weeks.
Ref.: 8
Guideline:
Species/strain:
Group size:
Test substance:
Batch:
Purity:
Dose levels:
Vehicle:

/
rat (Sprague Dawley)
5 males and 5 female, young and adult
Dow Corning 244 fluid
D4 lot LL106323
/
0 and 950 ppm (0 and 11.4 mg/l)
air at 20- 230C and 30-50% relative humidity
21

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

Exposure:
GLP:

6 h whole body inhalation
/

This was a 14-day whole body inhalation range-finding study. Dosing was for 6h/day for 14
consecutive days, followed by one week recovery. D4 vapour was diluted as necessary with
air. The target dose level (950 ppm) was difficult to generate as the saturated vapour
concentration is ~1000 ppm at 200C and 760 mm Hg. The average daily concentration was
854 ppm D4. Control group received pure air.
The animals were checked daily for clinical signs. Body weights and food consumption were
recorded every fourth day.
Results
No deaths or treatment-related signs were noted during the study. Adult females showed a
significant weight loss (-3 g) compared with the controls over the 2-week treatment period.
Adult males and young males and females gained approx. 40% and 30% less body weight
than controls respectively over the treatment period. Both adult and young rats showed
improved weight gain during the one-week recovery period. All treated rats ate slightly less
food than the controls during the treatment period. Appetites returned during the recovery
period. No clinical pathology or necropsy performed.
Ref.: 9
28-day
Guideline:
Species/strain:
Group size:
Test substance:
Batch:
Purity:
Dose levels:
Vehicle:
Exposure:
GLP:

OECD 412
Rat (Fischer 344 CDF Cr1BR SPF)
10 males and 10 females per dose
Dow Corning 244 fluid
D4 lot LL107568
>95% (96% octamethylcyclotetrasiloxane, 4% decamethylcyclopentasiloxane 0.1% hexamethylcyclotrisiloxane)
analysed as 0, 2.78, 5.13, 8.62 and 14.21/ 13.25 mg/l air
air at 20- 23 °C and 30-50% relative humidity
6 h nose only inhalation (male- 20, female -21 exposures in 28 d)
in compliance

D4 was administered to rats during a continuous 6-hour daily exposure for 5 days/week for
4 weeks.
Controls received untreated filtered air. The test dose levels were 2.5, 5, 9 and 16 (days 15) and 12 (days 6-29) mg/l, corresponding to approx. 226, 417, 700 and 1154/1076 ppm.
On analysis, the achieved levels were 2.78, 5.13, 8.62 and 14.21/ 13.25 mg/l air. The
saturated vapour concentration of D4 was evaluated to be 13 mg/l. Thus only the 3 lower
dose were vapour only. At the highest exposure level, 20% of the test atmosphere was
expected to be a liquid aerosol. The particle size was not measured.
The animals were checked daily for clinical signs. Body weights were recorded daily for
week 1 and then 3 times a week. Food consumption was recorded daily for week 1 and then
for 2-3 periods until the termination of the study.
Blood and urine samples were collected at the termination of the study for analysis. Postmortems were carried out on all animals. Organs were weighed and tissues preserved for
histopathology and liver samples for electron microscopy.
Results
There were no deaths at the two lower doses during the treatment period. One control
female and one male from the high dose were found dead on post-mortem day. The cause
of death did not seem to be treatment related. At the highest dose, 3 females were found

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

dead on Day 2 and 6. As a result the exposure dose was reduced. However a fourth female
was found dead on Day 7.
The mean bodyweights and body weight gains of the animals at the highest exposure dose
was marginally reduced throughout the study compared with the lower exposure doses, but
some were statistically significant compared with the control.
There was statistically significant decreased food consumption at the highest concentration
for Days 1-9. After that food consumption was comparable with that of other exposure
routes in males. In females there was a compensatory effect from Day 16 onwards.
Clinical signs (e.g. hunched posture, stiff or abnormal gait, head tilt and ruffled fur)
increased dose-dependently at 5 mg/l and above, with sedation, excitement and tremor in
some high dose animals after Week 1.
Biochemical changes noted suggest metabolic adaptation or stress that was treatment
related. The results were equivocal as there was great variation within groups.
Increased absolute and relative liver weights were seen in all treated groups, increased
absolute and relative adrenal weights and reduced absolute and relative thymus weights in
males at the highest exposure and females at both top exposure doses. These were all
statistically significant (p varied between 0.01 - 0.05).
The study authors proposed that increased adrenal weights at the highest exposure indicate
that the carbohydrate, protein and fat metabolism may be the result of altered
adrenocortical functional activity.
Macroscopically, there was pulmonary focal or reddish discolouration in all groups. These
were not considered to be treatment related. All other changes were considered incidental.
Histopathological changes: In all animals exposed to the test vapour, the lungs showed
minimal to slight alveolar inflammation. There was a minimal to slight goblet cell
proliferation in the nasal cavity at the highest exposure.
An increase in vaginal mucification was seen in females.
In the two highest exposures, hepatocellular hypertrophy was seen. There were dosedependent ultrastructural changes in hepatocytes in all treated groups. An increase in the
smooth endoplasmic reticulum was seen at the 2 highest exposure doses. There were
decreases in relative mitochondria volume at all exposure doses and a reduction in rough
endoplasmic reticulum at most higher doses.
Vacuolation of the zona fasciculata of the adrenal cortex was evident in most of the animals.
Thymic atrophy was seen in all animals but was most pronounced at the highest
concentration.
The NOAEL was considered to be <226 ppm (2.8 mg/l air).

Guideline:
Species/strain:
Group size:
Test substance:
Batch:
Purity:
Dose levels:
Vehicle:
Exposure:
GLP:

Ref.: 10

/
Mouse, CD-1; Guinea pig, Hartley; Hamster, Golden Syrian; and
Rabbit, New Zealand White
10 males and 10 females per dose except rabbit 5 male/female
Dow Corning 244 fluid
D4 lot LL107568
≥97% octamethylcyclotretrasiloxane (impurities were D5 and D3)
0 and 700 ppm (0 and 8.4 mg/l)
air
6 h whole body inhalation for 28 days
in compliance

This was a multi-species 28-day repeated dose inhalation study.
The animals were checked daily for clinical signs. Body weights and food consumption were
recorded every 4 days except in rabbits, where it was every second day.
23

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

Results
No deaths or treatment-related signs were noted during the study. Males showed nonsignificant slightly lower average body weight gains over study period. Food intakes were
similar for males and females throughout the study.
Guinea pigs were unaffected by treatment. Increased relative liver weights of mice and
female hamsters appeared to be treatment-related although no histopathological changes
were noted.
Exposure to 700 ppm for 28 consecutive days had no significant effect on body weight or
food intakes of mice, hamster and rabbits.
Ref.: 11
Guideline:
Species/strain:
Group size:
Test substance:
Batch:
Purity:
Dose levels:
Vehicle:
Exposure:
GLP:

/
Rat, Sprague Dawley CD; Mouse, CD-1; Hamster, Golden Syrian; and
Rabbit, New Zealand White
10 males and 10 females per dose except rabbit 5 male/female
Dow Corning 244 fluid
D4 lot AJ844
≥99.7%
0, 10, 700 ppm (0, 0.12 or 8.4 mg/l)
air
6 h whole body inhalation, 5 days/5 weeks
in compliance

This was a multi-species 35-day repeated dose inhalation study with 14 day recovery period
to characterize species differences of liver response by studying urinary metabolites,
induction of liver enzymes and cell replication.
The animals were checked daily for survival and clinical signs. Body weights and food
consumption were recorded on Day 1 and at termination. Urine was collected from 5
animals /sex/group on days 1, 3, 12, 19 and 25. On days 3 and 25, these samples analysed
for Me2SiO (D) and MeSiO3/2 (T) moieties. Cell replication assays were performed on 10
male and 10 female rats/group exposed to 700 ppm for 6h/day for 3 or 5 days and on a
group of rats exposed for 5 days followed by a 14 day recovery period. These animals had
an osmotic pump implanted subcutaneously, Exposure Day-1 and in the recovery group
Recovery Day 9. These were loaded with 2 ml BrdU (25mg/ml). 2000 cells were counted.
All animals were autopsied and liver weights were recorded.
To investigate possible enzyme induction, glutathione-S-transferase, epoxide hydrolase, and
ethoxycumarin deethylase were measured. 5 male and 5 female rats and guinea pigs from
each group were exposed to 0 or 700 ppm (6h/5d).
Results
No mortality or overt signs of toxicity occurred in any of the treated or control groups.
A statistically significant increase in liver weights was observed in male and female
hamsters, mice, and rats exposed to 700 ppm D4, but there was no change in guinea pigs
and rabbits.
Urine sampled on day 3 and day 25 were analysed for Me2SiO (D) and MeSiO3/2 (T)
moieties. Demethylated D4 (MeSiO3/2, T) ranged from 1-9 ppm in the low dose and from 40
to 400 ppm in the high dose group. The amount of T in the different species roughly follows
the order: Hamster+Mice>Rat>Rabbit>Guinea Pig. The Me2SiO (D) to T ratio was similar in
all species. There was a correlation between the amount of T produced and liver weight
increase. Metabolism showed no gender specificity. Exposure of female rats to 700 ppm D4
for five days induced hepatic cell proliferation. After the exposure, there was a return to
control levels. In males this effect was also seen with BrdU but not equally clear with mitotic
cells.
D4 did not induce the enzymes assayed in guinea pigs. All 3 enzymes, glutathione-Stransferase, epoxide hydrolase, and ethoxycumarin deethylase, were induced in male rats.
24

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

In female rats epoxide hydrolase and ethoxycumarindeethylase were induced but not
glutathione-S-transferase.
Conclusion
This study shows a reversible increase in rat liver weight and increased appearance of
demethylated D4 moiety in the urine of hamster, mice and rat. In addition, this study shows
enzyme induction and increased hepatocyte proliferation in rats but not guinea pigs. All
these observations indicate the presence of an adaptive metabolic change.
Ref.: 12
3.3.5.2.

Sub-chronic (90 days) oral / dermal / inhalation toxicity

Whole body inhalation studies
Guideline:
Species/strain:
Group size:
Test substance:
Batch:
Purity:
Dose levels:
Vehicle:
Exposure:
GLP:

/
Rats (Sprague Dawley)
see below (Subgroups A, B and C–E)
Dow Corning 244 fluid
D4 lot LL019901
/
0, 5, 10 or 300 ppm (0, 0.06, 0.12 or 3.6 mg/l)
air
6 h whole body inhalation 5 days/week
in compliance

This was a 13-week inhalation exposure study in rats. The control and high exposure dose
had 50 males and 20 females. These were subdivided into 5 subgroups. Subgroup A (10
male/female) were treated for 13 weeks. Subgroup B (10 male/female) were treated for 13
weeks with a 4 week recovery period before autopsy. Subgroups C and D (10 male) were
exposed for 4 weeks. Subgroup E (10 male) were exposed for 13 weeks period and killed.
The low and mid exposure dose were treated for 13 weeks.
Subgroups A and B formed the basic 13 week study. Subgroups C, D and E were assigned
for special morphometric studies. However since liver weights were not elevated in
Subgroup C after 4 weeks, Subgroups D and E were kept for 13 weeks before being killed
but the liver weights were still not elevated, they were discarded.
The animals were checked twice daily for clinical signs. Body weights and food consumption
were recorded weekly. Ophthalmological examination, haematology, biochemistry and urine
were tested at 3 months and at end of recovery period.
At post mortem, all organ weights were recorded and histopathology of a complete set of
tissues from high dose group and controls, and with nasal cavity, trachea, larynx, lungs and
liver from low and mid exposure groups.
Results
High dose females had increased liver weight (~28%) at the end of the 13 week exposure
period, but it was comparable to controls after the 4 week recovery period. There were no
other exposure-related abnormalities in clinical signs, food consumption, body weights,
haematology, serum biochemistry, urinalysis, ophthalmology, or macroscopic or microscopic
tissue evaluations. No exposure related histopathological findings were found at 13 weeks
or after the 4 week recovery period. There was no pathological evidence of hepatomegaly.
It was concluded that the NOEL was 10 ppm.
Ref.: 13
Guideline:
Species/strain:

/
Rats (Sprague Dawley)

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

Group size:
Test substance:
Batch:
Purity:
Dose levels:
Recovery group:
Vehicle:
Exposure:
GLP:

Control and high dose 20 males/females, low and mid dose 10
males/females
Dow Corning 244 fluid
D4 lot LL107568
~97% D4 (primary impurities were D3 and D5)
0, 50, 300 or 700 ppm (0, 0.6, 3.6 or 8.4 mg/l)
4 weeks for 10/sex control and high dose
air
6 h whole body inhalation 7 days/week for 13 weeks
in compliance

The animals were checked daily for clinical signs. Body weights and food consumption were
recorded weekly. Ophthalmological examination, haematology, biochemistry and urine were
tested at 3 months and at end of recovery period.
At post mortem, all organ weights were recorded and histopathology of a complete set of
tissues from high dose group and controls and with nasal cavity, trachea, larynx, lungs and
liver from low and mid exposure groups.
Results
No mortality or overt signs of toxicity were recorded. A slight, reversible reduction in body
weight gain was noted in high exposure females. There were no other exposure-related
abnormalities in haematology, serum biochemistry, urinalysis, ophthalmology. Liver weights
increased in all male exposed groups and in the mid and high exposure females. This liver
weight increase was reversible in males but not in females. A decreased ovary weight at the
high exposure dose was noted in the recovery group only. No other exposure related
histopathological findings were found at 13 weeks or after the 4 week recovery period.
It was concluded that the NOEL was 50 ppm in females and less than 50 ppm in males
based on liver weights.
Ref.: 14
Nose only inhalation study (3 months)
Guideline:
Species/strain:
Group size:
Test substance:
Batch:
Purity:
Dose levels:
Vehicle:
Exposure:
Recovery:
GLP:

OECD 412 (1991)
Rats (Fischer 344).
Control and high dose 30 males/females, low and mid dose 20
males/females
Dow Corning 244 fluid
D4 lot LL023S10
>99.42%
0, 35, 122, 488 or 898 ppm (0.42, 1.48, 5.91 and 10.87 mg/l)
air
6 h nose only inhalation 5 days/week for 13 weeks
4 weeks Control and high dose 10 males/females
in compliance

Mean temp, 20 –22 °C, relative humidity 2.7-3.3%
The animals were checked daily for clinical signs. Body weights and food consumption were
recorded weekly. Haematology, biochemistry and urine were tested at 3 months and at end
of recovery period. Ophthalmological examination of control and high exposure animals was
at the end of treatment and recovery
At post mortem, all organ weights were recorded and histopathology of a complete set of
tissues from high dose group and controls and with lungs, adrenals, heart, kidney, liver,
lymph nodes, spleen and thymus and all affected tissues from lower exposure level groups.

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

Results
Deaths were recorded only in females in the high exposure group (3 during week 1, one
during week 7 and one during week 9). These were accompanied by hunched posture and in
one, a stiff gait. All animals in the high exposure group had reduced body weights and body
weight gains and decreased food intake. In the recovery group, weight gain became
comparable with the controls.
Males showed a significant decrease in erythrocytes in the 2 highest exposure groups,
whereas both sexes showed increased MCV. At the high exposure, mean corpuscular
haemoglobin decreased in both sexes. These persisted during the recovery period.
Significant alteration in blood biochemistry (increases in gamma-glutamyl-transferase and
alanine aminotransferase in male and female, in total cholesterol, slight decreases in
triglyceride in both male and female, phospholipids in males, and total bilirubin in females)
occurred in the low-mid exposure and above. During the recovery period, these returned to
levels comparable with the control.
There was a significant increase in lung weight at the high dose at the end of the treatment
period, but after the recovery period, lung weights were comparable with the controls. Liver
weights increased in females in all groups from the low-mid exposure and above and in
males in the high-mid exposure and above. In addition, females had increased adrenal
weights and slightly reduced thymus weights at the high-mid and highest exposure and
markedly reduced ovary weights at highest exposure. These were resolved by the end of
the recovery period.
Histopathological changes were:
•
•
•
•

increased incidence and severity of goblet cell proliferation in the nasal cavity at the
highest dose
increased alveolar macrophage foci in the lungs in all treated groups
chronic interstitial inflammation of the lungs in all treated groups
vaginal mucification and increased incidence of ovarian atrophy at the highest exposure

All these effects were reversible or showed a clear tendency for reversibility.
Ref.: 15, AR 3
Comment
The increased liver weights suggest a NOEL of 35 ppm. Moreover, it was concluded that the
LOEL was 35 ppm based on the presence of lung lesions at all exposure levels. The lung
effects are not considered relevant in relation to the use of cosmetics.
3.3.5.3.

Chronic (> 12 months) toxicity

Guideline:
Species/strain:
Group size:

Test substance:
Batch:
Purity:
Dose levels:
Vehicle:
Exposure:
GLP:

/
Rats (F344)
10 rats/sex/dose group (sacrificed after 12 months of exposure; see
below: Subgroup B)
20 rats/sex/dose group (exposed to D4 for 12 month and sacrificed after
a 12 month recovery period; see below: Subgroup C,)
octamethyltetracyclosiloxane
D4 lot LL084732
/
0, 10 ppm, 30 ppm, 150 ppm or 700 ppm (0, 0.12, 0.36, 1.82 or 8.49
mg/l)
air
6 h whole body inhalation 5 days/week; see below (Subgroups B and C)
in compliance

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

Four studies were performed with F344 rats. The rats (7 – 8 weeks when the exposure
started) were exposed by whole-body inhalation to concentrations of 0, 10 ppm, 30 ppm,
150 ppm, or 700 ppm D4 (LL084732 >99% pure) (mol weight 296.62, air concentration [0,
121, 364, 1820 or 8492 mg/m3] 6 hrs/day, 5 days/week. Tissue Level Study (Subgroup
A): 6 rats/sex/group, the animals were sacrificed after 6 months of exposure. Chronic
Toxicity Study (Subgroup B): 10 rats/sex/group, the animals were sacrificed after 12
months of exposure. Chronic Recovery Study (Subgroup C): 20 rats/sex/group, the
animals were exposed to D4 for 12 month and sacrificed after a 12 month recovery period.
Oncogenicity Study (Subgroup D): Described in section 3.3.7. on carcinogenicity.
The survival of Subgroup C when assessed after 12 months of recovery showed no
significant difference between the exposed and the control groups of either sex. There was
no early death in either Subgroup A or B prior to their scheduled sacrifices. There were no
clinical signs that were clearly associated with D4 exposure. Ocular examination conducted
two weeks prior to the scheduled sacrifices for Subgroups B and D did not reveal eye lesions
clearly associated with D4 exposure.
Clinical pathology parameters were measured at 3, 6, 9, and 12 months on study. Overall
erythrocyte and urinalysis parameters of either sex were not affected by D4 exposure.
Leukocytosis was consistently observed in both sexes of rats exposed to 700 ppm at all time
points, resulting from increased lymphocytes. There was an exposure related decrease in
aspartate aminotransferase (AST), alanine aminotransferase (ALT), creatine kinase (CK),
and lactate dehydrogenase (LDH) activities in D4 exposed rats of both sexes at 3, 6, 9, and
12 months of exposure. These decreases were frequently present in a dose-related manner,
in particular at the 6- and 9-month time-points. No clear toxicological significance of the
decrease in serum enzymes was identified relative to histopathology findings.
Selected organs were collected and weighed at the scheduled sacrifices. Weight increases in
the liver, kidney, and uterus were of particular interest. At 6 months on study (Subgroup
A), the absolute liver weight tended to increase with increasing D4 exposure concentration
and the difference was statistically significant at 700 ppm for females and at 30 ppm for
males, respectively, relative to the concurrent controls. At 12 months (Subgroup B), the
absolute liver weights were significantly increased at 150 and 700 ppm compared to
controls for both sexes and the relative liver weights (normalized either to body or brain
weight) generally increased with increasing exposure concentrations. The liver weight
increase might be associated with centrilobular hypertrophy of hepatocytes diagnosed in
700-ppm males in Subgroup B. The absolute and/or relative kidney weights increased in
some exposed males and females at 12 months, but the differences were statistically
significant at 700 ppm when compared with the controls.
Conclusion
In this study, a NOEL of 10 ppm was identified based on increased liver weights in males
after 6 months. A NOAEL of 150 ppm was set based on increased liver weights and on
centrilobular hypertrophy of hepatocytes diagnosed after 12 months in males receiving 700
ppm.
Ref.: 79; AR 4
Conclusion on repeated dose toxicity
D4 has been evaluated for its safety in a range of toxicity studies by different routes of
exposure. A NOAEL of 960 mg/kg bw was found in a study in rabbits with dermal application
of D4 for 28 days. Repeated dose studies at relatively high oral and inhalation doses
revealed few systemic effects. Clinical signs of toxicity were minimal and the histological
changes observed were reversible. A reversible liver enlargement (hypertrophy) and
phenobarbital-like increases in xenobiotic metabolising enzyme activities are considered to
be an adaptive response to xenobiotics, reversible upon cessation of exposure and not
associated with overt hepatotoxicity. From the chronic toxicity study, a NOAEL of 150 ppm
was derived, based on non-neoplastic changes (increased liver weights and centrilobular
hypertrophy of hepatocytes in male rats receiving 700 ppm D4 for 12 months). This NOAEL

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

for repeated dose toxicity equals the NOAEL of 150 ppm in the carcinogenicity study (see
below and section 3.7) and was used in the MOS calculation.
The respiratory tract changes in the nose and lungs are local effects in line with exposure to
a mild, non-specific irritant. This change was reversible and not relevant for D4 exposure
from cosmetics.
In the combined chronic toxicity and carcinogenicity study, D4 caused endometrial
adenomas only at 700 ppm; the NOAEL was 150 ppm (see section 3.3.7). Other nonneoplastic effects (liver weight increases) in this study were observed at 150 ppm D4 in
female rats. Effects on liver were also observed in subchronic toxicity studies with D4, with
either inhalation exposure or oral administration: The oral LOEL for liver weight increase
with D4 in rats and rabbits was 500 mg/kg bw/d. Liver weight increases after subchronic
inhalation of D4 (≥ 35 ppm) were reversible upon cessation of exposure.
Other studies evaluating changes in liver weight and hepatic enzyme activities upon
inhalation or oral dosing with D4 are reported in section 3.3.12 (special studies).
3.3.6.

Mutagenicity / Genotoxicity

3.3.6.1.

Mutagenicity / Genotoxicity in vitro

Bacterial gene mutation assay
Guideline:
Test system:
Replicates:
Test substance:
Batch No.:
Concentrations:
GLP:

/
Salmonella typhimurium, TA98, TA100, TA1535, TA1537, TA1538
Triplicate plates, two independent assays, preincubation method
D4 in ethanol (100 mg/ml)
AJ844, purity 99.7 – 99.8%
100 – 5,000 µg/plate with and without metabolic activation
In compliance

D4 (in ethanol) was tested for mutagenicity in the reverse mutation assay on bacteria both,
with and without metabolic activation (S9 fraction from the liver of Aroclor 1254 induced
Sprague-Dawley rats) in the standard plate test (SPT). The Salmonella typhimurium strains
TA 98, TA 100, TA 1535, TA 1537, and TA1538 were exposed to the test substance at
concentrations ranging from 100 µg/plate to 5,000 µg/plate (with and without S9 mix). For
control purposes solvent (water) and positive controls (without S9 mix: 4-nitro-ophenylendiamine for strain TA 98 (10 µg/plate); sodium azide for strain TA100 and TA1535
(10 µg/plate), and 9-aminoacridine for strain TA 1537 (60 µg/plate); with S9 mix: 2aminoanthracene for all strains (2.5 µg/plate).
Results
No mutagenic activity was observed in any of the five strains tested, either by evidence of a
dose-response relationship or a doubling of the mean number of colonies over the mean
control level, either in the absence or presence of S9 activation. These results were
observed in two independent experiments. All five bacterial strains exhibited mutagenic
response to the appropriate positive control substance. Negative (solvent) controls were
also tested with each strain and the mean numbers of spontaneous revertants were
considered acceptable.
Ref.: 49
Chromosome aberration test in cultured Chinese hamster ovary (CHO) cells
Guideline:
Test system:

/
Chinese hamster ovary cells (CHO-K1-BH4) (subclone D1) from Oak
Ridge National Laboratory, USA
29

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Replicates:
Test substance:
Batch:
Concentrations:
GLP:

Duplicate culture in a single experiment
D4 in ethanol
AJ844, purity 99.7 – 99.8%
Without S9: 0.3 – 10 µg/ml, with S9: 3 – 30 µg/ml.
In compliance

D4 was assessed for its potential to induce structural chromosome aberrations in Chinese
hamster ovary (CHO) cells in vitro in the presence and absence of metabolic activation (S9
mix prepared from Aroclor 1254 induced Sprague Dawley rats). The test article was
dissolved in ethanol. Duplicate cultures of CHO cells were exposed to the test substance for
4 hours at concentrations of 0.3, 1, 3, 6 and 10 µg/ml in the non-activation assay and for 4
hours at concentrations of 3, 6, 10, 20 and 30 µg/ml in the presence of metabolic
activation. After treatment, D4 was removed. Fresh medium containing 3 µg/ml of BrdU and
5% serum was added to each culture and cultures were incubated at 37oC for an additional
24 to 26 hours. 2 – 3 hours prior to harvest, cultures were exposed to colchicine. Following
harvest, cells were fixed on slides, stained and examined for chromosomal aberrations. 100
metaphases from each duplicate culture were analyzed. Triethylenemelamine (TEM) 1.5
µg/ml for the non-activation set and cyclophosphamide (CP) 20 µg/ml requiring activation
served as positive control substances. A solvent control (ethanol) was also included in the
test.
Results
No unusual types or distribution of aberration were observed. Endoreduplication was
observed in both replicates at 30 µg/ml in the presence of metabolic activation, but was not
evaluated quantitatively. The significance of this finding is not known. The positive controls
were highly effective in producing significant numbers and types of chromosome damage,
demonstrating the responsiveness of the test system.
Conclusion
Under the conditions of the assay described, D4 did not induce an increase in cells with
structural chromosome aberrations in the presence and absence of metabolic activation
system.
Ref.: 50
Sister chromatid exchange (SCE) in cultured Chinese hamster ovary (CHO) cells
Guideline:
Test system:
Replicates:
Test substance:
Batch:
Concentrations:
GLP:

/
Chinese hamster ovary cells (CHO-K1-BH4) (subclone D1) from Oak
Ridge National Laboratory, USA
Duplicate culture in a single experiment
D4 in ethanol
AJ844, purity 99.8%
Without S9: 0.03 – 3 µg/ml, with S9: 3 – 30 µg/ml.
In compliance

D4 was assessed for its potential to induce sister chromatid exchange in Chinese hamster
ovary (CHO) cells in vitro in the presence and absence of metabolic activation (S9 mix
prepared from Aroclor 1254 induced Sprague Dawley rats). The test article was dissolved in
ethanol. Duplicate cultures of CHO cells were exposed to the test substance for 4 hours at
concentrations of 0.03, 0.1, 0.3, 1, and 3 µg/ml in the non-activation assay and for 4 hours
at concentrations of 3, 6, 10, 20, and 30 µg/ml in the presence of metabolic activation.
After treatment, D4 was removed. Fresh medium containing 3 µg/ml of BrdU and 5% serum
was added to each culture and cultures were incubated at 37oC for an additional 24 to 28
hours. 2 – 3 hours prior to harvest, cultures were exposed to colchicine. Following harvest,
cells were fixed on slides and stained for SCE. The number of chromosomes and the number
of SCE in a minimum of 25 cells for each duplicate culture were scored. Only metaphases
30

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___________________________________________________________________________________________

containing 20 ± 2 centromeres were scored for SCE. The centromeric switch of label was not
scored as a SCE. The mean numbers of SCE/cell and SCE/chromosome were calculated.
Ethylmethane-sulfonate
(EMS)
100
µg/ml
for
the
non-activation
set
and
dimethylnitrosamine (DMN) 300 µg/ml requiring activation served as positive control
substances. A solvent control (ethanol) was also included in the test.
Results
The SCE frequencies for the culture medium controls were in the acceptable range. The
positive controls were highly effective in producing significant numbers of SCE
demonstrating the responsiveness of the test system.
Under the conditions of the assay described, D4 did not induce an increase in SCE in CHO
cells in the absence of metabolic activation system. D4 produced statistically significant
increases in the incidence of SCE in the presence of S9 metabolic activation. These
increases were not considered dose-related and were of such small magnitude that they
were considered not to be of biological relevance.
Ref.: 51
3.3.6.2.

Mutagenicity / Genotoxicity in vivo

Chromosome aberration test in Sprague Dawley rats
Guideline:
Test system:
Replicates:
Test substance:
Treatment:
Batch:
Concentration:
GLP:

/
Male and female Harlan Sprague Dawley rats approx. 8 weeks old at
start
of treatment.
Five animals/sex/treatment group/sampling time.
D4 vapour diluted with air.
Rats were exposed to D4 vapour for 6 h/day for 5 consecutive days
AJ844, purity 99.7%
700 ppm. The daily mean chamber concentration achieved was 720 ppm
and the mean nominal concentration was 836 ppm.
In compliance

D4 was assessed for its potential to induce chromosome aberrations in the bone marrow
cells of male and female Sprague Dawley rats at 6 h and 24 h after exposure to D4 vapour
for 6 h/day for 5 consecutive days at target concentration of 700 ppm. The animals were
sacrificed by carbon dioxide asphyxiation 6 or 24 h after the last treatment. Colchicine was
injected 2 – 3 h prior to sacrifice. A femur was removed from each rat and the bone marrow
was flushed into a centrifuge tube. Cells were centrifuged, fixed and stained. Initially, one
slide was prepared for each animal. Five animals/sex/treatment group/sampling time were
used. When possible, 100 metaphase cells/animal were evaluated for incidence and type of
chromosome damage. Negative controls were exposed to filtered air using the same
exposure regimen as for the treated rats. Positive control rats were exposed to filtered air
and subsequently injected with 30 mg/kg cyclophosphamide as a single intraperitoneal
injection after the fifth exposure and approximately 24 h prior to sacrifice.
Results
No statistically significant or exposure-related increases in the incidence of cells with
chromosomal aberrations were observed in rats of either sex at the 6 h or 24 h sampling
intervals. The positive control cyclophosphamide produced significant numbers and types of
damage with both male and female rats.
Ref.: 52
Comment
There is no evidence for D4 reaching the bone marrow under the conditions of exposure.

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
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Dominant lethal assay in Sprague Dawley rats
Guideline:
Test system:
Replicate:
Test substance:
Treatment:
Batch:
Concentrations:
GLP:

OECD 426 (August 21, 1981; FR 42472)
Male and female Sprague Dawley rats. Males were 10 – 12 weeks old,
females were younger (no age given)
15 males/group
D4, undiluted.
Male rats dosed orally for five days a week for 8 weeks. Mating with two
females/male followed. Female killed 14 days after mating confirmed by
presence of sperm in vagina
Number not quoted, purity >99.6% by gas chromatography.
High dose – 1000 mg/kg/day (maximum allowable dosage volume)
Intermediate dose – 500 mg/kg/day
Low dose – 100 mg/kg/day
In compliance

D4 was assessed for its potential to induce dominant lethal damage in Sprague Dawley rats.
A preliminary acute toxicity study failed to reach the maximum tolerated dose (MTD) within
the restrictions of maximum allowable dosage volume. Therefore, the MTD was assumed to
be 1000 mg/kg/day. Groups of 15 males received 100, 500 or 1000 mg D4/kg/day by oral
gavage for 5 days/week for 8 weeks prior to mating. The positive control group received
0.05 mg/kg/day triethylenemelamine (TEM) and a negative control group received tap
water. On week nine, dosing ceased and each male was supplied two virgin female rats.
When the presence of sperm was detected in the vagina, the females were removed and
housed individually. Females were sacrificed 14 days after mating and at necropsy the
ovaries and uteri were examined. The numbers of corpora lutea and living and dead
implantations were counted for each pregnant female.
Results
Uterine dissection of the pregnant females 14 days after confirmation of mating revealed no
evidence of a treatment-related effect on corpora lutea, implant counts or on litter size. The
positive control group utilising TEM produced a significant reduction in fertility, an increase
in dead implants and a decrease in litter size, thus validating the test system. It is
concluded that the test gave no evidence of D4 inducing chromosomal damage in germinal
tissue.
Ref.: 53
Conclusion on mutagenicity
The negative results obtained in bacteria (reverse mutation assay) or in mammalian cells,
i.e. in vitro chromosomal aberration and SCE assays in vitro, along with an in vivo
micronucleus assay and dominant lethal test, indicate that D4 does not possess genotoxic
potential.
3.3.7.

Carcinogenicity

Four studies were performed with F344 rats. The rats (7 – 8 weeks when the exposure
started) were exposed by whole-body inhalation to concentrations of 0, 10, 30, 150 or 700
ppm D4 (LL084732 >99% pure) (air concentration [0, 012, 0.36, 1.82 or 8.49 mg/l] 6
hrs/day, 5 days/week. Tissue Level Study (Subgroup A): 6 rats/sex/group, the animals
were sacrificed after 6 months of exposure. Chronic Toxicity Study (Subgroup B): 10
rats/sex/group, the animals were sacrificed after 12 months of exposure. Chronic
Recovery Study (Subgroup C): 20 rats/sex/group, the animals were exposed to D4 for 12
month and sacrificed after a 12 month recovery period. Oncogenicity Study (Subgroup
D): 60 rats/sex/group, the animals were exposed to D4 for 24 months and subsequently
sacrificed. Only the oncogenicity study is described below.

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

A complete histopathology examination was performed on all animals that were either
sacrificed or died in extremis. The percent survival of animal exposed to 700 ppm was
decreased (38% in treated males compared to 58% for controls and 58% in treated females
compared to 72% for controls). The survival in the other groups was similar to that found in
the control groups. It is stated that this effect on mortality was likely due to early onset and
increased incidence of mononuclear cell leukaemia (MNCL) that occurred at 700 ppm. The
terminal mean body weights and weight gains of the 700-ppm male rats were significantly
lower than those of the controls (∼6 and 8%, respectively). This difference from the controls
was apparent only during the last few months of study. No other exposure-related effect on
body weight was noted in the male groups. In females, there were a few occasions during
the study when exposed groups had significantly different body weight from the control.
This occurred sporadically and the difference from the controls was minor.
Statistically significant increases in absolute and relative kidney weights in both sexes were
observed in the high dose group. It is stated that these increases in kidney weights may
reflect the observed increases in severity of chronic nephropathy. Statistically significant
increases in absolute and relative liver weights were observed in males in the high dose
group and in females at the two highest dose groups. There were no accompanying
histopathological effects.
A 51% increase in absolute and relative uterine weight was seen in the high dose female
rats. Histopathologically the total incidence of cystic endometrial hyperplasia was 78%
compared to 19% in the control group. Four of the 35 (11%; p<0.04) female animals in the
high dose group that survived two years were diagnosed with endometrial adenomas. No
uterine adenomas were diagnosed in the intercurrent mortality animals or in any of the
other groups.
The neoplastic effect observed in the high dose (700 ppm) female rats has been attributed
to a hormonal dysregulation resulting from interaction of D4 with the dopamine D2receptor.
Pre-treatment of F344 rats with sulpiride, a dopamine receptor antagonist, blocked the
effect of D4 on the serum prolactin levels suggesting that D4 acts on the pituitary as
dopamine D2-receptor agonist in vivo (Ref. AR 5). These results and the known species
differences in reproductive physiology provide support for a potential mode of action that is
not relevant for humans. Additional investigations on the mode of action are described in
Section (3.3.12. Special studies).
The frequency of mononuclear cell leukaemia (MNCL) in male rats was: 73% in the controls
(43/59; historical controls 474/1059 [45%]; p < 0.0001), 10-ppm group 45% (27/60), 30ppm group 43% (26/60), 150-ppm group 48% (29/60), and 700-ppm group 69% (41/59).
The frequency of MNCL in the high dose group is similar to the control. The frequency in the
control group was significantly higher than in the historical controls. This finding is not
discussed by the study authors. However, it is stated that the incidence of MNCL was
increased in early death and moribund sacrificed males exposed to 700 ppm compared to
male controls. This increase was statistically significant (p < 0.05) using the Peto analysis.
It is apparent that the frequencies of MNCL in the 10 ppm and 30 ppm groups are similar to
the historical controls. If the MNCL in the 700 ppm group is compared to the 10 ppm group,
the increase in the 700 ppm group is significant (p<0.0094). No increase in MNCL was
found among the exposed female rats. It is likely that a threshold exists in the induction of
MNCL. If it is considered that the very high frequency in the control group may be
erroneous, the NOAEL for MNCL induction is 150 ppm (320 mg/kg bw/d).
Ref.: 79, AR 4
Comment
In the lifetime study with D4, uterine (endometrial) adenomas and hyperplasia were
observed at the highest dose level of 700 ppm. The lack of a genotoxic potential supports
the view that tumour formation by D4 is due to threshold effects. The applicant has
proposed that the endometrial adenomas and hyperplasia are due to dopamine-agonist like
activity of D4 and thus not relevant to humans. But, this position is not supported to date
33

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___________________________________________________________________________________________

by international reviews due to a lack of a published data and a thorough mode of action
analysis.
An increased incidence of mononuclear cell leukaemia was observed in male rats. Since this
tumour type is unique to F344 rats, its relevance to humans is questionable. Thus, SCCS as
well as Health Canada (Ref.: AR 8) dismissed this tumour type in their evaluations of D4.
3.3.8.

Reproductive toxicity

3.3.8.1.

Teratogenicity (Embryo-foetal developmental studies)

The effects of D4 on embryo-foetal development have been investigated in rats and rabbits.
The study designs and the results are summarised in the following table:
Table 4: Embryo-foetal development studies
Species/stra
in

Route

Treatment

No./grou
p

Dose levels
of D4

Results

Ref.*

Maternal
toxicity at ≤50
mg/kg. No
teratogenicity
Maternal
toxicity at 700
ppm. No
teratogenicity
Maternal
toxicity at 300
ppm. No
teratogenicity

Maternal
toxicity at 700
ppm. No
teratogenicity
Maternal
toxicity at 500
ppm. No
teratogenicity

DOSE RANGE-FINDING STUDIES
Rabbit/New
Zealand White

Oral
gavage

Daily oral doses on
GD7 through GD19

0, 50, 100,
500, 1000
mg/kg/day

Rat/Sprague
Dawley

Whole
body
inhalation

6h/day on GD6
through GD15

0, 10, 100,
300, 700 ppm

Rabbit/New
Zealand White

Whole
body
inhalation

6h/day on GD6
through GD18

0, 10, 100,
300, 700 ppm

EMBRYOFOETAL TOXICITY STUDIES
Rat/Sprague
Dawley

Whole
body
inhalation

6h/day on GD6
through GD15

30F

0, 100, 300,
700 ppm

Rabbit/New
Zealand White

Whole
body
inhalation

6h/day on GD6
through GD18

20F

0, 100, 300,
500 ppm

GD = gestation day, F = female
* The studies summarized in this table refer to GLP studies
Dose range-finding studies were conducted in pregnant Sprague Dawley rats (Ref. 22)
and New Zealand White rabbits (Ref. 23) with whole body exposure to D4 vapour
concentrations of 10, 100, 300 or 700 ppm. Also, an oral gavage study was conducted in
pregnant New Zealand White rabbits at D4 dose levels of 50, 100, 500 or 1000 mg/kg/day
(Ref. 24). Rats were exposed on gestation days (GD) 6 through 15 whereas rabbits were
exposed on GD7 through 19 (oral study) or GD6 through 18 (inhalation study). On gestation
day 20 (rats) or 29 (rabbits), the dams were killed for Caesarean section and uterine
examination.
In the oral study in rabbits, the death of one rabbit in the 500 mg/kg/day group on GD
26 was considered unlikely to be treatment-related in the absence of death at 1000
mg/kg/day (Ref. 24). Clinical signs included mucoid stool at 500 and 1000 mg/kg/day,
anogenital staining and hair loss at 1000 mg/kg/day, and tissue and/or red fluid on cage
tray (often associated with abortion) at 500 and 1000 mg/kg/day. Body weight and food
consumption reductions were recorded at all D4 dose levels. Treatment-related abortions
were observed at 500 and 1000 mg/kg/day with markedly increased post implantation

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losses at 1000 mg/kg/day. This correlated with reductions in the number of live foetuses
and gravid uterine weights at 1000 mg/kg/day.
By gestation day 13 most rabbits at 500 or 1000 mg/kg/day were consuming less than 20
g/day or not eating at all. Therefore, it is considered likely that the increase in abortions
and post implantation losses are the consequence of reduced food consumption and not a
direct effect of D4.
This conclusion is substantiated by an oral gavage study in non-pregnant rabbits at dose
levels of 500 or 1000 mg/kg/day for 14 days (Ref. 6). These doses caused marked
reductions in food intakes and body weights, similar to those seen in the reproductive study
(Ref. 24) indicating the foetal losses in the earlier study were probably due to weight loss
and stress and not to the direct action of D4.
In the inhalation dose-range finding studies in rats and rabbits, there was no
treatment-related maternal mortality, although both rats and rabbits showed reduced food
consumption and reduced body weight gains at 700 ppm. Rabbits exhibited decreased
defecation, soft stool and/or anogenital staining at 300 and 700 ppm. In neither species was
there any evidence of developmental toxicity.
Embryofoetal toxicity studies were conducted by whole body inhalation exposure of 30
dams/group at dose levels of 100, 300 or 700 ppm (rats) (Ref. 25), and of 20 dams/group
to 100, 300 or 500 ppm (rabbits) (Ref. 26). Rats and rabbits were exposed for 6 hours/day
on gestation days 6 through 15 (rats) or gestation days 6 through 18 (rabbits).
All animals survived the treatment period with no overt signs of toxicity. Food consumption
was reduced in rabbits at 500 ppm and in rats at 700 ppm although a reduction in body
weight gain was only noted for rats. Reproduction and Caesarean parameters were not
affected by treatment. Morphological evaluation of the foetuses did not demonstrate any
test article-related malformations or developmental variations.
The NOAEL for maternal toxicity was 300 ppm for rats and rabbits. D4 was not teratogenic
at the highest dose levels tested, i.e. 700 ppm for rats and 500 ppm for rabbits.
Conclusion
Embryofoetal inhalation studies in Sprague Dawley rats and New Zealand White rabbits
revealed no evidence of developmental toxicity (teratogenicity) up to the highest dose levels
tested, i.e. 700 ppm for rats and 500 ppm for rabbits.
Ref.: 22, 23, 24, 25, 26
3.3.8.2.

One-generation studies (general reproduction and fertility)

A series of one-generation studies with inhaled D4 has been conducted: They include two
range finding (Refs. 27, 28), two male (Refs. 29, 30) and one female (Ref. 31) crossover,
and two “phased female” (Refs. 32, 33) studies in rats. (Note: A two-generation study has
also been completed and is described in section 3.3.8.3.)
In all these studies male and/or female Sprague Dawley rats were exposed by whole body
vapour inhalation to D4 at concentrations ranging from 70 ppm to 700 ppm for 6 hours/day,
7 days/week. The general protocol for each study was similar and included continuous
exposure for at least 28 or 70 days prior to mating, with exposure to females continuing in
some studies throughout gestation and lactation.
The study designs and results of these studies are summarized below in two tables: The
first table describes range-finding studies; the second one describes the phased-female
studies.

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

Table 5: One-generation range-finding inhalation studies
Species/
strain

Treatment

Nr/group

Rat/Sprag
ue Dawley

Males and
females exposed
6h/day for 28
days prior to
mating, throughout mating to
GD 21, then LD
4 to termination
Males and
females exposed
6h/day for 28
days prior to
mating,
throughout
mating to GD 20
Males exposed
6h/day for 70
days prior to
mating,
throughout
mating to GD 13

F0 – 20M,
20F

Dose
levels of
D4
0, 70, 700
ppm

F0 – 22M,
22F

Males exposed
6h/day for 70
days prior to
mating,
throughout
mating
Females
exposed 6h/day
for 70 days prior
to mating,
throughout
mating to GD 21
and from LD 3 to
21

Rat/Sprag
ue Dawley

Results

Ref.
*

F0 females on
LD 21
F1 pups on
PND 28

Parental toxicity at 700
ppm; reduced number of
implantation sites at 700
ppm. No postnatal
toxicity.

0, 700
ppm

F0 females on
LD 4, F1 pups
on PND 4

Parental toxicity at 700
ppm. No postnatal
toxicity.

F0 – 40M,
40F
(females
exposed to
filtered air
only)

0, 500,
700 ppm

Toxicity to F0 males at
700 ppm. No toxicity at
500 ppm or to F1 pups.

F0 – 22M,
22F
(females
exposed to
filtered air
only)
F0 – 22M,
22F
(males
exposed to
filtered air
only)

0, 70,
300, 500,
700 ppm

F0 females and
F1 pups on
PND 21. -- F0
males 5 weeks
later following
a 5 week
recovery
period
F0 males after
mating, F1
pups on PND
4, F0 females
following F1
pups
F0 males after
mating, F0
females on LD
21, F1 pups on
PND 28,

No parental or neonatal
toxicity at 70 or 300
ppm.

No maternal toxicity at
70 ppm. No postnatal
toxicity at 70, 300 or
500 ppm

0, 70,
300, 500,
700 ppm

Termination
day

GD = gestation day, LD = lactation day, PND = postnatal day, M = males, F = females F0 =
Parent generation, F1 = First generation
* The studies summarized in this table are GLP compliant
Results
In one range-finding study (Ref. 28), the gestation length was reported to be statistically
significantly increased compared to concurrent controls (21.8 days in control and 22.3 days
in the treatment group); however, the gestation length in the treated group was within the
historical control range for the laboratory (21.5-22.8 days). Exposure to D4 did not have
any treatment-related effects on pup viability as measured by the number of pups born
dead or the pup viability indices on postnatal days (PND) 1 and 4 (Refs. 27, 28).
The major findings noted in females exposed to D4 at 700 ppm in the two range-finding
studies (Refs. 27, 28) and in the two studies (described below) in which treated females
were mated to control males (Refs. 31, 33), and at 500 ppm or 700 ppm in the “phased
female” study (Ref. 32) were statistically significant treatment-related decreases in: number
of corpora lutea, number of uterine implantation sites, total number of pups born, and mean
live litter size. These parameters are all inter-related in that the number of eggs ovulated
(represented by the number of corpora lutea) should be equivalent to the number of
implantation sites, the number of foetuses, and therefore the potential litter size. The mean
live litter size in the 700-ppm exposure groups was consistently 60% to 70% of the control

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

values. Yet, while the mean live litter size was decreased in the higher exposure groups, the
percentage live births of the total number of pups born was comparable to control values.
A clinical observation noted in some of these studies (Refs. 27, 28, 29, 30) was an apparent
increase in ejaculatory plugs in male rats exposed to D4. However, when the number of
ejaculatory plugs was expressed as number of plugs/rat/day, the values were all within the
historical control range for this parameter, indicating that there was no effect of D4 on
ejaculatory plug production in male Sprague Dawley rats.
No effects on the number of uterine implantation sites, the litter size, or the mean live litter
size were found in the male crossover studies (Refs. 29, 30) in which males were
exposed to D4 concentrations up to 700 ppm and were mated to control (unexposed)
females. In these studies, exposure to D4 did not affect sperm production, motility, or
morphology, nor did it result in either weight changes or histopathological changes of male
reproductive or accessory sex organs. Therefore, it can be concluded that the effects on
litter size are not male-mediated.
Phased female studies
Two studies were conducted (i.e., “phased-female” studies) in which female rats were
exposed to D4 during selected phases of the reproductive cycle (Refs. 32, 33). In these
studies females were mated with unexposed males. The design and results of these studies,
recently also published in a peer reviewed article (Ref. AR 14) are summarised in table 6.
Table 6: One-generation “phased-female” inhalation studies (males unexposed)
Species/
Strain
Rat/Sprag
ue Dawley

Rat/Sprag
ue Dawley

Treatment

No./group

Dose
levels
of D4
0, 70,
300,
500, 700
ppm

Termina
tion day

Overall phase: females
exposed 6h/day for 28
days prior to mating and
until GD 19

24 F

Ovarian phase:
females exposed 6h/day
for 31 days prior to
mating until 3 days before
to mating (total 28 days
exposure)
Fertilisation phase:
females exposed 6h/day
for 3 days prior to mating,
throughout mating period
until GD 3
Implantation phase:
females exposed 6h/day
from GD 2 through GD 5

60F
(30F
controls)

0, 700
ppm

GD 20

60F
(30F
controls)

0, 700
ppm

GD 20

24F

0, 700
ppm

GD 20

Premating phase:
Gps 2-5: single 6h
exposure on 1,2,3 or 4
days prior to mating. Gp 6
- 6h/day exposure from 3
days prior to mating until
one day before mating. Gp
7 6h/day exposure from 3
days prior to mating
through to GD3.

25F in Gp 1,
125F total in
Gps 2-5,
125F / Gp 6,
70F in Gp 7

0, 700
ppm

GD 8

GD 20

Results

Ref
.*

Maternal toxicity at
300 ppm and above
due to food and body
weight decreases.
Reduced number of
corpora lutea at >300
ppm and foetal
survival at ≥500 ppm.
Food and body weight
decreased. Number of
corpora lutea and
foetal survival
unaffected

Food and body weight
decreased. Number of
corpora lutea reduced
and lower intrauterine
survival
Lower food intakes
and body weights
during GD 2 – 6.
Number of corpora
lutea and foetal
survival unaffected
Maternal and
reproductive toxicity
expressed by effects
on body weight gains,
reduced food intakes
and reduced corpora
lutea and implantation
sites

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
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Species/
Strain
Rat/Sprag
ue Dawley

Treatment

Post mating phase:
Single 6h exposure on
GD0 (Gps 2-5), on GD1
(Gp 3), or GD2 (Gp4), or
daily from GD0 through
GD2 (Gp 5).

No./group

25F

Dose
levels
of D4
0, 700
ppm

Termina
tion day
GD 8

Results

Ref
.*

Maternal toxicity
expressed by reduced
body weights gains
and food consumption
in GD0 through GD2
group.

GD = gestation day, LD = lactation day, PND = postnatal day
M = males, F = females
Gps 1-6 = group number in phase study
* The studies summarized in this table are GLP compliant
In the first “phased-female” study, four groups of female rats were exposed to D4 by whole
body inhalation for 6 hrs/day according to the following schedule:
-

Overall Phase: Groups of 24 female Sprague Dawley rats were exposed to D4 at
concentrations of 70, 300, 500, or 700 ppm beginning at least 28 days prior to mating
and continuing through gestation day (GD) 19.
Ovarian Phase: Sixty female rats were exposed to 700 ppm beginning 31 days prior to
mating and stopping three days prior to mating.
Fertilisation Phase: Sixty female rats were exposed to 700 ppm for three days prior to
mating and continuing through to GD3.
Implantation Phase: Sixty females were exposed to 700 ppm from GD2 through to
GD5.

In the Overall phase study, the following observations were made: a reduction in the
number of corpora lutea (300, 500 and 700 ppm), reduction in the number of uterine
implantation sites and foetuses (500 and 700 ppm), an increase in pre-implantation loss
(500 and 700 ppm), and increased post-implantation loss (700 ppm).
No significant effects were noted on the number of corpora lutea or indices of intrauterine
survival in females exposed at 700 ppm in the Ovarian and Implantation phase studies. In
the Ovarian phase study, no effects were seen on uterine implantation sites, viable
foetuses, or on any other reproductive parameters measured.
In the Fertilisation phase study, the numbers of corpora lutea, uterine implantation sites,
and viable foetuses were reduced at 700 ppm (the only dose tested) while the mean preimplantation and post-implantation losses were increased. The effects on corpora lutea and
intrauterine survival were similar for both the fertilization phase in which exposure began 3
days pre-mating and continued through gestation day 3 and the overall phase in which
exposure began 28 days pre-mating and continued through gestation day 19.
A second study was performed to investigate the relative temporal responsiveness of female
rats to D4 (Ref. 33). Female Sprague Dawley rats were treated by whole body exposure to
700 ppm D4 vapour for 6 hrs / day with the following regimens:
–
–
-

Pre-mating phase:
a single 6-hour exposure, on either the first (D-1), second (D-2), third (D-3) or fourth
(D-4) day prior to mating
daily 6-hour exposures from three days prior to mating until one day prior to mating (3
exposures)
daily 6-hour exposures three days prior to mating through a two-day mating phase and
until gestation day 3 (8 exposures)
Post-mating phase
a single 6-hour exposure on either gestation days 0, 1 or 2
daily 6-hour exposures from gestation day 0 until gestation day 2 (3 exposures)

Maternal and reproductive toxicity were expressed in the pre-mating phase by a reduced
pregnancy rate in the group exposed one day before mating (Day –1 group), but not in
38

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groups exposed on Days –2, -3 or –4, and by effects on mean body weight gains in the
group exposed from 3 days before mating until one day prior to mating, and by effects on
mean body weight gains, reduced food consumption, reduced numbers of corpora lutea and
implantation sites, increased numbers of small implantation sites, and reduced mean
uterine weights in the group exposed from 3 days before mating until gestation day 3.
Apart from the reduced pregnancy rate in the group exposed one day before mating (Day –
1 group), no impairment in pregnancy rates was observed in any other group. The
temporal nature of this effect in the Day –1 group was demonstrated by the lack of effect
on pregnancy rates of animals exposed two, three or four days before mating.
Maternal toxicity was expressed in the post-mating phase by reduced mean body weight
gain and food consumption in the gestation day 0 through GD 2 group. There was no
evidence of reproductive toxicity in parameters monitored through the uterine examination
on gestation day 8.
Conclusion
The
weight-of-the-evidence
from
the
above
studies
indicates
that
octamethylcyclotetrasiloxane’s effect on fertility occurs some time around the time of
ovulation, i.e. within the 24 hours before mating.
Ref.: 27 to 33; AR 14
3.3.8.3.

Two-generation study (reproduction toxicity and developmental neurotoxicity)

Guideline:
Species/strain:
Group size:
Treatment:
Dose level:
Test substance:
Batch no:
GLP statement:

2-generation study protocol (EPA OPPTS test guidelines)
Rats, Sprague Dawley (Crl:CD IGS BR rats)
groups of 30 male and 30 female (F0 and F1)
Inhalation exposure for 6 hours daily for at least 70 consecutive days
prior to mating, and during mating, and gestation until day 20 and
during lactation day 5 to termination.
0, 70, 300, 500 or 700 ppm
D4
Lot # LL0847; purity at least 99.7 %
yes

In a 2-generation study with D4 following the US EPA OPPTS (Office of Prevention,
Pesticides and Toxic Substances) protocol, groups of 30 male and 30 female Sprague
Dawley rats (F0) were exposed to 70, 300, 500, or 700 ppm D4 for 6 hours daily for at least
70 consecutive days prior to mating, and during mating, and gestation until day 20 and
during lactation day 5 to termination. Exposure of F1 females at the same concentrations
was from weaning (i.e. day 22) through the second F1 mating and to gestation day 20 (i.e.,
about 274 days of age). A control group of males and females were exposed to filtered air
on a comparable regimen.
Animals were checked twice daily for clinical signs. Their food consumption and body
weights were recorded at intervals. All females were allowed to rear their pups to weaning
(lactation day 21). F0 males and females were necropsied after weaning F1 pups. Following
weaning the F1 pups were selected to produce F2a and F2b litters. F2a pups were selected
for neurobehavioral and neuropathological examination. All decendents were necropsied.
Selected tissues were examined microscopically from F0 and F1 adults in control and 700
ppm groups, and from all F0 and F1 parental animals dying during the study.
The results of this study are summarized as follows:
Toxicity parameters:
Deaths: Two F0 females at 700 ppm died of dystocia and two had liver necrosis and
kidney failure, which may have been contributory factors to their deaths. One F1
female at 500 ppm died of dystocia and one female at 700 ppm died with liver
necrosis as a possible contributory factor. The relationship of treatment to these
events is uncertain.
39

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Reductions in mean body weight gain for F0 at 500 and 700 ppm and for F1 at 700
ppm.
Organ weight changes: in F0 animals: statistically significantly increased kidney
weights in males at 300, 500 and 700 ppm, statistically significantly increased liver
weights in females at 300, 500 and 700 ppm and in males at 700 ppm. In F1 animals:
statistically significantly increased kidney weights in males at 500 and 700 ppm and
females at 700 ppm, statistically significantly increased liver weights in males and
females at 300, 500 and 700 ppm and statistically significantly increased pituitary
gland weights in 700 ppm females.
Renal tubular mineralization: increased incidence at 500 and 700 ppm (F0 and F1),
statistically significant at 700 ppm only.
Hepatocyte hypertrophy: increased incidence at 500 and 700 ppm (F0), at 70, 300,
500 and 700 ppm (significant only at 500 and 700 ppm)(F1) with hepatic pigment at
300, 500 and 700 ppm (F1) and bile duct hyperplasia at 500 and 700 ppm (F1)
Thyroid follicular cell hypertrophy at 700 ppm (F1)
Lung interstitial inflammation and alveolar histiocytosis: The F0 incidence: (control,
70, 300, 500 and 700 ppm, respectively) was in males:1/20 (control), 0/30, 4/30,
1/29, 5/28 and in females: 0/30 (control), 7/30, 5/30, 7/30, 8/26. The F1 incidence of
alveolar histiocytosis was in males: 10/30 (control) vs 22/29 (700 ppm); in females:
3/30 (control) vs 8/30, 9/30, 7/29, 13/29 and interstitial inflammation was increased
at 700 ppm only, males: 3/30 in controls vs 10/29, females: 4/30 in controls vs 9/29.

Reproduction parameters:
Reduced mating and fertility indices occurred in F1 animals at 700 ppm. In the second
F1 mating, the indices were reduced in all treated groups, but, the difference from
controls only attained statistical significance at exposure concentrations ≥ 500 ppm.
Reductions in mean live litter size and mean number of pups born were recorded at
500 and 700 ppm (F0, F1). Similar changes (not statistically significant) were noted
sporadically at 70 and 300 ppm in both F0 and F1 animals without a clear doseresponse relationship
Extended parturition and/or dystocia: in F0 females: two (of 30) at 500 ppm and three
at 700 ppm; in F1 females: one each at 300, 500 and 700 ppm. The relationship of
treatment to these events is uncertain.
Increased oestrous cycle length noted in F1 females at 700 ppm
Histopathological change: There were no reported changes in ovary, uterus, vagina,
mammary gland and pituitary gland in F0 animals. In F1 animals, oestrus cycle
irregularities, reductions in corpora lutea and reduced numbers of pregnancies were
reported. However, there was no clear dose-response and the differences from
controls were only obvious at 700 ppm. The subtle change reported in the ovaries
(anovulatory), and mammary glands (ductal/acinar proliferation and evidence of
secretion) were considered to be part of the oestrous cycle perturbation. Effects seen
in the F1 generation were possibly a combination of D4’s effect on the LH surge as well
as a slight acceleration of the spontaneous process of reproductive senescence in the
F1 females.
The differences in general toxicity responses between the F0 and F1 generations after
inhalation of D4 were minimal. Overall the responses were slightly more severe in F1 than
in F0 animals except for respiratory tract reactions. In reproduction toxicity, it is interesting
to note a general lack of response to D4 treatment in the F0 generation compared to the F1
generation. This may be associated with the small difference in age at start of treatment (F0
– 44 days old, F1 – 22 days old).
Ref.: 34; AR 15

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

Conclusions on Reproductive Toxicity
There is no evidence that D4 causes developmental toxicity in rats or rabbits or an adverse
effect on male rat fertility. However, the following effects on female rat fertility were
identified:
-

An effect on fertility which occurs at ovulation apparently with reduced numbers of
eggs ovulated as demonstrated by the ‘phased’ studies in female rats.
Decreases in number of corpora lutea, number of uterine implantation sites, total
number of pups born, and mean live litter size were noted in the one-generation
general reproduction and fertility studies at high exposures. Two multidose studies (0,
70, 300, 500 or 700 ppm) allow estimates of NOAELs. In one study (Ref. 31),
reductions in reproductive parameters were recorded only at 700 ppm, while in the
other study (Ref. 32), reduced implantation sites and viable foetuses and increased
pre-implantation losses were noted at 500 and 700 ppm. In addition, reduced
numbers of corpora lutea were found at ≥ 300 ppm. However, as the reduction in
corpora lutea was marginal at 300 ppm (14.6/dam vs. 16.2/dam in controls) without a
clear exposure-related response and within the range of values in the historical control
database, (14.2/dam-20.5/dam), the NOAEL is considered to be 300 ppm.
Similar reproductive changes were recorded in the two-generation study at 500 and
700 ppm, but, in addition increased oestrous cycle length in F1 females at 700 ppm as
well as increased pituitary gland weights were noted. Also in F1 females there were
histopathological changes in ovaries and mammary glands at all exposure levels.
These histopathological changes were:
1)
2)
3)
4)

minor, and not clearly treatment-related except at 700 ppm,
reported only in the F1 and not in the F0 generation,
similar in nature to those found in concurrent controls and,
considered to be probably a combination of D4’s effect on the LH surge, as well
as a manifestation of the spontaneous, age-related waning of the female
reproductive system in the rat (i.e. F1 female Sprague Dawley rats were about
274 days of age at sacrifice),

Considering these points, it appears justified to set 300 ppm as the NOAEL.
General comment on reproductive toxicity
From the reproductive toxicology studies and taking the weight of evidence approach for
reproduction parameters, the NOAEL is considered to be 300 ppm.
There is evidence (see Special studies, section 3.3.12.) suggesting that the effect of D4 on
reproduction in females is due to a delayed ovulation caused by a treatment-related delay in
or blockage of the luteinising hormone surge on the day of pro-oestrus. The reproduction
findings in the two-generation study are consistent with a long-term suppression of LH
release.
3.3.9.

Toxicokinetics

Octamethylcyclotetrasiloxane (D4), randomly labelled with carbon-14, was used in a
number of studies to examine its absorption, distribution, metabolic fate and elimination
following oral, inhalation and intravenous administration to rodents and/or humans.
Oral Study
Guideline:
Species/strain:
Group size:

/
female Fisher 344 rats
49 (preliminary groups I (15), II (26) and III (8))
41

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

Test substance:
Batch:
Purity:
Test formulation:
Dose level:
GLP statement:

183 (definitive groups I (122) and II (61))
D4
14
C-D4, specific activity of 2.0 mCi/mmol
D4, lot n° LL084732
14
C-D4, lot n° 921217
D4, approximately 99% (GC/MS)
14
C-D4, 99.2 (radiochemical purity by HPLC)
14
C-D4 diluted with unlabeled D4 dosed orally in corn oil, Emulphor,
Simethicone fluid, or neat
Dosing solutions prepared to achieve a radioactivity concentration of
approximately 25µCi and a nominal dose of 300 mg/kg D4. Rats
received a single oral dose.
in compliance

Absorption was studied in female Fischer rats following a single oral dose of 300 mg/kg
C-D4 in corn oil, Simethicone fluid or undiluted. Absorption of radioactivity, expressed as
percentage of total recovered radioactivity from urine, carcass, expired volatiles and expired
CO2 was 51.95±4.97%, 12±1.21% and 28.14±5.78% with 14C-D4 in corn oil, Simethicone or
neat, respectively. The area under the curve (AUC) generated from blood data also
indicated D4 was most readily absorbed when delivered in corn oil (AUC in µg 14Cequivalents D4•hr/g of blood was 933±26 and AUC in µg D4• hr/g of blood was 159±17) and
least available in Simethicone fluid (AUC in µg 14C-equivalents D4•hr/g of blood was 77±13
and AUC in µg D4• hr/g of blood was 19±5). Blood radioactivity concentrations were highest
24 h after dosing.
14

Conclusion
An oral dose of D4 is rapidly absorbed when administered in corn oil, with radiolabelled D4
in tissues generally following plasma levels. Examination of the blood radioactivity and
parent D4 concentration and the mass balance of radioactivity indicated that D4 was most
readily absorbed when delivered in corn oil and least available for absorption when
administered in Simethicone fluid. Qualitative assessment by Whole-Body autoradiography
showed comparatively similar patterns of absorption and disposition of radioactivity, but
differences in transit time of radioactivity through the gastrointestinal tract following
administration of 14C-D4 in the various carriers or neat. This study indicated that the oral
absorption of D4 can be significantly influenced by the carrier used to deliver D4.
Ref.: 35
Whole Body Inhalation study
Guideline:
/
Species/strain:
Rat, Fisher 344 CDF(F-344)/CrlBR
Group sizes
Absorption study: 81 males and 13 females. Additional 8 males and 8 females were used
to measure respiratory minute volume (RMV)
Elimination study: 56 males and 8 females
Test substance:
D4
14
C-D4, specific activity of 30.1 mCi/mmol
Batch:
D4, lot number LL024S10, purity 99.8% by GC-MS
14
C-D4, lot number 940512, radiochemical purity 99.58% (HPLC),
Test formulation: 14C-D4 diluted with unlabeled D4 vapour
Dose level:
700 ppm for 6 hours
GLP statement:
Yes
The rats were divided into subgroups to determine 1) retention and total body burden of
radioactivity 2) tissue distribution of radioactivity up to 7 days post exposure, and 3)
elimination of radioactivity – up to 7 days post exposure.
42

SCCS/1241/10
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___________________________________________________________________________________________

Results
Based on the mean total body burden and the achieved dose, the percent 14C-D4 retained
by the animals during the 6 hour exposure was 5.63% of the delivered radioactivity.
Radioactivity was readily taken up in tissues. Maximum concentrations in most tissues were
observed at the end of exposure. In blood and plasma, Cmax was achieved at 1 and 3 h,
respectively. In fat, the tissue exhibiting the highest concentration of radioactivity, Cmax
was achieved at 12 h post exposure. Except for fat, the elimination of radioactivity from the
tissues was at approximately the same rate as from plasma. The apparent terminal
elimination t1/2 was 13 h in blood, 59 h in plasma and ranged from 34 h to 158 h in tissues.
Most of the radioactivity was recovered as expired volatiles (30.68±2.26%) and by renal
excretion (urine, 47.01±2.49%). The faecal recovery was 12.33±0.95%. Approximately
10.56±0.53% of the body burden (mainly muscle, fat and bones) was recovered in the
carcasses at 168 h. The overall recovery as expired 14CO2 was low (1.83±0.21% body
burden) indicating that its formation was not a major route of elimination.
No 14C-D4 was detected in the urine samples pooled over the collection intervals up to 48 h
indicating that the retained 14C-D4 was rapidly metabolized. Radioactivity in urine and
faeces was mainly due to polar metabolites.
Ref.: 36
Nose only Inhalation Studies
Guideline:
Species/strain:
Group size
Absorption study:
Elimination study:
Test substance:
Batch:
Test formulation:
Dose level:
GLP statement:

/
Rat, Fisher 344 CDF(F-344)/CrlBR
191 male and 189 female. Groups of 50 males and 50 females
50 males and 50 females
D4
14
C-D4, specific activity of 30.1, 33.2 and 39.7 mCi/mmole
D4, lot number LL024S10, purity 99.8% by GC-MS
14
C-D4, lot number 940512, 940519 and 940809 radiochemical purity
99.58%- 99.8%
14
C-D4 mixed with unlabeled D4
7, 70 or 700 ppm for 3 hours (4 animals/sex/group) or 6 hours (46
animals/sex/group)
Yes

Results
Actual mean achieved chamber D4 concentrations were 7.52, 70.4 and 716 ppm (exposure
29.0 - 40.4 µCi; body burden corresponding to 1.595 – 2.203 µCi). The overall recoveries of
the radioactivity (% of body burden) in the excreta were: urine (39.9 – 42.3% male and
32.3 – 43.1% female; faeces (12.3 – 14.6% male and 9.53 – 14.0% female); expired
volatiles (25.7 – 27.3% male and 23.2 – 34.8% female); expired CO2 (0.59 – 5.24% male
and 0.38 – 5.42% female); cage wash (1.34 – 2.84%).
Plasma values of 14C-D4 at the three concentrations (7, 70 and 700 ppm) showed an
increase that was approximately proportional to increasing dose (see Table below)
Table 7: Concentration of radioactivity (µg eq/ml) in blood and plasma after a 6hour nose only exposure
Males
Blood
Plasma
Females
Blood

7 ppm

70 ppm

700 ppm

0.270±0.013
0.349±0.018

2.21±0.12
2.875±0.044

14.16±1.00
16.15±1.53

0.248±0.019

1.54±0.16

11.13±1.17

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

Plasma

7 ppm
0.310±0.031

70 ppm
1.728±0.288

700 ppm
11.14±1.73

Of the delivered radioactivity 4.99 - 5.47 % was retained in males and 5.19 - 5.52 % in
females with no apparent gender or dose effect 6 hrs post nose-only exposure. Radioactivity
was readily taken up by the tissues, especially by fat, and was eliminated at rates similar to
or somewhat slower than from plasma. Maximum concentrations were observed at end of
exposure to 3 h post exposure (except fat). Radioactivity in fat was sustained up to 48 h
post exposure. Except for fat and adrenals (and to a lesser extent, trachea and pancreas)
there was no apparent gender effect in the blood, plasma or tissue radioactivity AUC values.
Except for the testes the combined (male and female) mean radioactivity t1/2 ranged from
68 h in plasma to 154 h in skin. There were no apparent gender or dose effects in the
terminal elimination half-lives. The tissues having the longest half-lives were testes
(combined mean t1/2, 273 h), skin, lung, nasal mucosa, fat, eye, uterus and vagina.
Increases in the tissue radioactivity AUC values were generally proportional or less than
proportional to the increase in exposure level except for fat, uterus and vagina which
showed higher than proportional increases. Small amounts of radioactivity were recovered
in all tissues analyzed at 168 h: the total (sum of the mean values) ranged between 0.442
and 0.793% of the body burden. The excretion of radioactivity was mainly via the
pulmonary (expired volatiles: 23.2 – 34.8%; expired CO2: 0.38 – 5.42%) and renal routes
(urine: 32.3 – 43.1%), and to a lesser extent via faeces (9.53 – 14.6%). Elimination of
radioactivity was most rapid during the first 0 - 12 h interval and more prolonged up to 7
days (168 h).
Ref.: 37
Guideline:
Species/strain:
Group size:
Test substance:
Batch:
Test formulation:
Dose level:
GLP statement:

/
Rat, Fisher 344 CDF(F-344)/CrlBR
50 males and 50 females
Subsets:
Absorption:
5 males / 5 females
Elimination:
4 males / 4 females
D4
14
C-D4, specific activity of 36.4 mCi/mmole
D4, lot number LL024S10, purity 99.8% by GC-MS
14
C-D4, lot numbers 950309 and 951031 radiochemical purity 99% and
98.2%,
14
C-D4 mixed with unlabeled D4
7 and 700 ppm unlabelled D4, Day 1-14, 6 hour nose-only followed on
Day 15, single 6 hours exposure to 14C-D4
in compliance

Following exposure to 14C-D4, each group was divided into subsets. 5 animals per sex were
killed immediately following exposure and a further subset kept in metabolic cages to collect
urine, exhaled volatiles, faeces and CO2 at intervals up to 168 h post exposure. The
remainder were in subsets of 4 animals per sex, killed at 0, 1, 3, 12, 24, 48, 72, 96, 120,
168 h to check 14C-D4 in blood and tissues.
Results
The mean body burden of radioactivity in the animals at the end of the exposure was 1.486
– 2.170 µCi, corresponding to retained radioactivity ranging from 4.38 - 6.14 % with no
apparent gender or dose effects. In blood, plasma and all tissues, maximum concentrations
of radioactivity were observed between 0 h (end of exposure) to 3 h post exposure.
Radioactivity was readily taken up by the tissues, especially by fat (sustained up to 24-48 h
post exposure), and was eliminated at rates similar to or somewhat lower than from plasma
(t1/2 56 ± 10 h). High levels of radioactivity were found in the respiratory tract functionally
involved in the intake and elimination of the administered 14C-D4. AUC and Cmax values
were comparatively low in the reproductive tissues, somewhat higher in the liver, thymus,

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

lungs, nasal mucosa and highest in the fat. The increase in radioactivity (AUC and Cmax) in
whole blood, plasma, and all analyzed tissues was proportional or less than proportional to
the exposure level. With the exception of fat, the elimination profile in blood, plasma and
tissues appeared to be multiphasic and was characterized by an initial, relatively rapid
decline up to 24 h post exposure followed by a long apparent terminal elimination phase
(mean radioactivity t1/2 ranged from 56 h to 253 h); (mean radioactivity t1/2 ranged from 56
h to 155 h). The blood-to-plasma ratios were approximately 1 or somewhat lower over the
time course of the study indicating that the radioactivity was readily taken up by the red
blood cells and eliminated at approximately the same rate as from plasma. In each dose
group, the tissue-to-plasma ratios remained approximately the same or increased up to 168
h indicating that the rate of radioactivity elimination from tissues was approximately the
same or slower than that from plasma.
The tissues containing the highest amount of radioactivity were the liver and fat. There was
no apparent effect in the blood, plasma and tissue levels. Recovery of radioactivity in both
sexes in excreta was for both dosages (7 and 700 ppm): urine, 37.4 - 40.0 %; faeces, 12.6
- 19.1 %; expired volatiles, 25.9 - 35.4 %; expired 14CO2, 2.06 - 4.54 %; cage wash, 1.31 1.86 %. Significantly higher proportions of radioactivity were eliminated via the lung both
as volatiles and CO2 while a significantly lower proportion was eliminated via the gastrointestinal tract in the faeces at the high dose level when compared with the low dose level.
However, there was no significant dose level effect in the urinary recoveries. Based on
normalized values, the portion of radioactivity remaining in the carcasses at 168 h post
exposure ranged from 6.53 - 8.50 %. Small amounts of radioactivity were recorded in all
analyzed tissues at 168 h; the total (sum of the mean values) ranged between 0.193 and
0.468% of the body burden.
Ref.: 38; AR 16
Comment
In three inhalation studies, male F344 rats were exposed to 14C-D4 at 700 ppm for 6 hours
[Ref. 36], male and female F344 rats were exposed to 14C-D4 at 7, 70 or 700 ppm for 3 or
6 hours [Ref. 37], and male and female F344 rats were exposed to unlabelled D4 at 7 or
700 ppm for 14 consecutive days followed by a single 6-hour exposure of 14C-D4 at 7 or 700
ppm [Ref. 38; AR 16]. After 6 hours exposure, the percent of 14C-D4 retained by males
ranged from 5.23% to 5.96% and in females from 5.75% to 6.14% of the delivered
radioactivity, at 7 or 700 ppm, respectively. Similar retention levels were achieved in males
and females exposed to 7 or 700 ppm for 14 consecutive days. Plasma values of 14C-D4 at
the three concentrations (7, 70 and 700 ppm) showed an increase that was approximately
proportional to increasing dose (see Table 7, above). Radioactivity was taken up by the
tissues, especially fat, and was eliminated at rates similar to or somewhat slower than from
plasma. In blood, plasma and all tissues (except fat), maximum concentrations of
radioactivity occurred at 0 h (end of exposure) to 3 h post exposure.
Fat appeared to be a depot for radioactivity as maximum concentrations were sustained up
to 48 h post exposure. The combined (male and female) mean radioactivity t1/2 ranged from
68 h in plasma to 154 h in skin. Tissues having the longest half-life were testes, skin, lung,
nasal mucosa, fat, eye, uterus and vagina.
The data show that approximately 5-6% of an inhaled D4 dose is absorbed. Higher D4
levels were found in lung tissue and fat compared to other tissues although this could be
expected, as D4 is lipid soluble and would preferentially deposit in fat and highly lipophilic
tissues.

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

Intravenous Study
Guideline:
Species/strain:
Group size:
Group size:
Test substance:
Batch:
Test formulation:
Dose level:
Vehicle:
GLP statement:

/
Rat, Sprague-Dawley (CD)
10 males and 10 females
3 Groups of 10 rats
D4
14
C-D4, lot number 921210, radiochemical purity > 97 %, specific
activity of 1.48 mCi/mmole
Unlabelled D4, lot number AJ844, purity not provided
14
C-D4 mixed with unlabeled D4
intravenous 1.1 ml.: single 7 mg/kg, single 70 mg/kg repeat (x14) 7
mg/kg
Ethanol, Emulphor EL 620 and saline (0.9%) 1:1:7 by volume
in compliance

This was a toxicokinetics study in rats following intravenous administration of D4. 6 groups
of 10 animals / sex were assigned to determine different endpoints, (3 doses - for plasma
radioactivity kinetics/tissue distribution: 1 group - single low dose for excretion
balance/tissue distribution; 2 groups - low and repeat dose for whole body autoradiography)
were performed by liquid scintillation counting.
The whole-body autoradiography demonstrated that radioactivity was well distributed
throughout the animal shortly after administration. Male animals appeared to metabolize D4
more extensively than females. A greater proportion of the mean administered radioactivity
(AR) was excreted in male urine (48.1 %) and faeces (10.4 %) than in female urine (28.5
%) and faeces (7.9 %). The expired air of female animals contained more radioactivity than
that of male animals, 35.2 and 22.4 % AR respectively, but the expired air from male
animals contained more 14CO2 (6.5 % for males, 3.2 % for females). Retention of
radioactivity in the total tissues of animals 120 hours after dosing was 19.0 % in female
tissues and 11.3 % in male tissues. The tissue with the highest concentration of
radioactivity at 120 hours was fat with a higher concentration in female fat. There were no
marked differences in plasma radioactivity pharmacokinetics observed between males and
females following either 7 mg/kg or 70 mg/kg. A ten-fold increase in dose from 7 mg/kg bw
(66.1 µg.h/ml male and 48.3 µg.h/ml female) to 70 mg/kg bw (546 µg.h/ml male and
485.4 µg.h/ml female) resulted in a proportional increase in the AUC in males and females.
A comparison of the results after single and repeated dosing suggested no accumulation of
plasma radioactivity in males and females. The concentration of radioactivity in tissues
suggested an approximate proportional increase with dose. The concentration of
radioactivity in fat was higher in females than in males but was similar in the liver and
kidneys. Fat radioactivity concentration appeared to decline at a similar rate compared to
the other tissues sampled (liver, kidneys) after initial peaks but the rate appeared to be
slow. The concentration of radioactivity in the liver and kidneys was substantially lower than
that measured in fat 30 - 48 hours after dosing. In male animals this difference ranged from
5 - 15 times lower and in females 12 - 25 times lower at 7 mg/kg. The concentration of
radioactivity measured in the tissues after 14 consecutive doses of 7 mg/kg suggested that
radioactivity accumulated in the tissues: the concentrations measured were 4 - 5 times
higher in all tissues than after the single dose at 7 mg/kg. The whole-body autoradiography
demonstrated that radioactivity was well distributed throughout the animal within short time
after administration.
Ref.: 39
Conclusion
A single IV dose of 14C-D4 as a microemulsion at 7 mg/kg appeared to be more extensively
metabolized by male rats than by female rats. Peak concentrations of radioactivity in liver,
kidneys and lungs were seen 0.5 hours after dosing in both sexes. These concentrations
declined slowly up to the final sampling point 120 hours after dose administration. The
46

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

tissue with the highest concentration of radioactivity at 120 hours was fat, with a higher
concentration in females.
Additional kinetic studies in rats, with different routes of application (inhalation, i.v. per os),
focussed on Elimination and Metabolism
Guideline:
Species/strain:
Group size:
Test substance:
Batch:
Dose level:
GLP statement:

/
Rat, Fisher rats
3 animals (body burden), 5 sets 3 animals (tissue distribution); 3
animals (excretion)
D4
14
C-D4, specific activity of 39.7 mCi/mmole
D4, lot number LL084732, >99,7% by GC-MS
14
C-D4, lot number 941128, radiochemical purity 97.3% (HPLC with
radiochemical detector)
700 ppm for 6 hours
in compliance

This was a pilot study to determine the
6h nose only inhalation exposure to D4.

C-D4 vapour pharmacokinetics following a single

Results
Maximum concentration in blood, plasma and tissues was at the end of exposure period.
The total body burden of radioactivity, which was retained by the animals during the 6 hour
exposure was 6.53 %. Elimination of radioactivity from tissues was approximately at the
same rate as from plasma (except for perirenal fat and lung). The overall mass balance of
radioactivity in the excreta was the following: urine, 35.75 ± 1.09%; faeces 29.68 ±
2.84%; expired volatiles, 33.72 ± 14.72; expired CO2, 1.72 ± 0.10%; and cage washes,
0.24 ± 1.97%. After the inhalation exposure to 14C-D4, radioactivity was rapidly excreted
by the animals; in the first hour, 12.43 ± 3.36% of the body burden was exhaled.
Approximately 85% of the expired volatiles were recovered during the 0 – 24 hour interval
after removal from the inhalation chamber. In the urine most of the radioactivity (86%) was
recovered during the 0 – 48 hour interval after removal from the inhalation chamber.
Ref.: 42
Guideline:
Species/strain:
Group size:
Test substance:
Batch:
Test formulation:
Dose level:
GLP statement:

/
Rat, Fisher 344 and Sprague-Dawley IGS, female
groups of 4 or 5 rats
D4
14
C-D4, specific activity of 17.6 mCi/mmole
D4, lot number LL024S10, purity 99.8% by GC-MS
14
C-D4, lot number 9074-1, radiochemical purity > 98 %
14
C-D4 mixed with unlabeled D4
700 ppm 14C-D4 mixed with unlabeled D4 as a single 6 h nose only
exposure
Yes

The animals were divided into subsets:
body burden immediately post exposure;
cannulated animals for blood levels at 1, 2, 6, 12, 24, 48, 72, 96, 120 h and
tissue distribution from the same animals at 2, 12, 72 and 120 h
excretion group: in metabolic cages for 168h
Results
Fischer 344 rats retained a significantly higher amount (p<0.05) of radioactivity (8.3 ±
0.22%) than Sprague-Dawley rats (5.9 ± 0.13%) at the end of the 6-hour exposure.
47

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Excretion of retained radioactivity was similar in both strains, with similar amounts being
excreted in urine (25.5–32.2%), faeces (19.4–19.2%), expired volatiles (23.5-25.4%) and
expired 14CO2 (3.94-3.57) for female Fisher and Sprague Dawley IGS rats, respectively. The
concentration of radioactivity over time in blood and lung was also similar over the 168 hour
post exposure period while differences were seen in fat, liver, faeces and urine (AUC in µg
equivalent D4/g*hr was 21685 and 14036 for fat, 1778 and 1510 for liver, 1137 and 600
for faeces and 5175 and 6679 for urine) from Fischer 344 and Sprague-Dawley rats,
respectively. Analysis of fat for parent D4 revealed the concentration of D4 in these samples
was essentially the same as the concentration of radioactivity found in both strains. Analysis
of blood, liver, lung, faeces and expired volatiles samples for parent D4 demonstrated
differences in the percent of radioactivity that could be attributed to metabolites in blood
(61 vs. 81%), liver (18 vs. 49%), lung (82 vs. 90%), faeces (98 vs. 98%) and expired
volatiles (48 vs. 33%) for Sprague-Dawley vs. Fischer 344 rats, respectively. Fischer 344
rats generally showed a lower percentage of the total radioactivity present as parent D4,
suggesting that the Fischer 344 rats may more readily metabolize D4 as compared to
Sprague-Dawley rats. Faeces demonstrated the least amount of parent D4 present at 2%
and 2.3% for the female Fisher 344 and Sprague Dawley rats, respectively, suggesting that
D4 is largely metabolized prior to faecal excretion.
No parent D4 was found in the urine samples from either strain suggesting all radioactivity
present in the urine was as metabolites. The radioactivity present in the urine consisted
entirely of polar metabolites of D4. Two major metabolites comprising 70-100% of the
urinary radioactivity for both strains were identified as dimethylsilanediol [Me2Si(OH)2] and
methylsilanetriol [MeSi(OH)3]. No significant differences in urinary metabolism are found
between the Fisher 344 and Sprague Dawley rats. Following sacrifice at the 168 hour post
exposure time point the total percent of body burden dose remaining in the tissues
(combined) was 0.4% for female Fisher 344 and Sprague Dawley IGS rats. Radioactivity
remaining in the carcasses, mainly in muscle, bone and fat was 9.17% and 15.95% of the
body burden dose for female Fischer 344 and Sprague Dawley IGD rats, respectively. These
kinetic differences between female Sprague-Dawley and Fischer 344 rats suggest that there
may be important biochemical differences leading to a decreased metabolism of D4 in the
female Sprague-Dawley rat.
Ref.: 43
Guideline:
Species/strain:
Group size:
Test substance:
Batch:
Test formulation:
Pre-treatment:
Dose level:
GLP statement:

/
Rat, Fisher 344, female
Groups of 3 – 5
D4
14
C-D4, specific activity was 2.0 mCi/mmole
D4, lot LL084732, purity 99.8% (GC-MS)
14
C-D4, lot 921217, radiochemical purity 99.03%.
14
C-D4 mixed with unlabeled D4
Days 1-4, phenobarbital (80 mg/kg i.p.), 3-methylcholanthrene (30
mg/lg i.p.) or vehicle
Control groups either 0.9% saline, corn oil or no pretreatment.
Day 5, a single i.v. dose of 14C-D4 (70 mg/kg).
Additional group oral dose of 14C-D4 (70 mg/kg) no pretreatment
/

This was a pilot study to see if classical inducing agents such as Phenobarbital (PB) or 3methyl-cholanthrene (3-MC) altered the metabolism of D4.
Results
PB-pretreated rats excreted 55 % of the administered dose in the urine, while control and
3-MC-pretreated rats excreted 24 - 27 % over the same 72 hour period. Rats pretreated
with PB excreted 14 % of the dose as CO2, while 3-MC-pretreated and control rats excreted
less than 3 % as CO2. However, only 9 % of the dose was excreted as expired volatiles in
48

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PB-treated rats, while 3-MC-pretreated rats excreted 29 % and control rats excreted 38 %.
The majority of the expired radiolabelled material was collected in the volatile trap, which
suggests it was likely parent compound due to its higher volatility compared to its
metabolites. At 72 hours following administration of D4, 29 % of the dose remained in the
carcass of control rats and 35 % in 3-MC-pretreated rats compared with 7 % of PBpretreated rats.
Following a single oral dose of 14C-D4, 22 % of the dose was excreted as expired volatile,
while rats administered a single i.v. dose excreted 38 % over 72 hours. Urinary excretion
was similar between the different routes of D4 administration. At 72 hours i.v.-treated rats
excreted 24 % in the urine, while orally treated rats excreted 31 %. Elimination of 14CO2
appeared to be independent of the route of administration (3 % over 72 hours). Elimination
in the faeces was a minor route of excretion after i.v. administration (< 8 %), but
accounted for 29 % after oral dosing. This suggests that the majority (about 20%) of the
radioactivity excreted in the faeces following oral administration is most likely non-absorbed
dose. At 72 hours, 18 % (oral) and 29 % (i.v.) of the radioactivity remained in the carcass.
The parent compound was not excreted in the urines of the control or of either group of
pretreated animals over the 72 hr collection period. There were at least six metabolites in
urine collected from control and pretreated rats. The profile did not change over the 72 hr
collection period. The urinary profile in animals administered 14C-D4 via oral gavage was
quantitatively very similar to that seen in control rats administered 14C-D4 intravenously.
Conclusion
This study indicates that there were differences in the major route of excretion following
different routes of administration, that phenobarbital but not 3-MC pre-treatment increased
the amount and rate of urinary excretion of radioactivity following a single i.v. dose of 14CD4; however PB pretreatment did not change the metabolic profile of D4. This provides
compelling evidence for the involvement of PB inducible enzymes in the metabolism of D4 in
rats.
Ref.: 44
Guideline:
Species/strain:
Group size:
Test substance:
Batch:
Test formulation:
Dose level:
GLP statement:

/
Rat, Fisher 344, male and female
see study #8464 (Ref. 44) and Study #8496
D4
14
C-D4, specific activity was 2.0 mCi/mmole
D4, lot LL084732, purity 99.8% (GC-MS)
14
C-D4, lot 921217, radiochemical purity 99.03%.
unlabeled D4 mixed with 14C-D4
single i.v. dose of 70 mg/kg
/

This was a pilot study to determine the urinary metabolites of D4
Results
Analysis was performed using an HPLC system equipped with a radioisotope detector. The
metabolites identified have clearly established that some demethylation occurs at the
silicon-methyl bond. The 2 major metabolites, constituting 75 - 85 % of the total
components, were identified as dimethylsilanediol [Me2Si(OH)2] and methylsilanetriol
[MeSi(OH)3]. Formation of MeSi(OH)3 clearly established demethylation at the siliconemethyl bonds of D4. No parent D4 was present in urine. The minor metabolites identified
[MeSi(OH)2-O-Si(OH)2Me],
[MeSi(OH)2-O-Si(OH)Me2],
were
[MeSi(OH)2-O-Si(OH)3],
[Me2Si(OH)-O-Si(OH)Me2], [Me2Si(OH)-OSiMe2-OSi(OH)Me2].
Ref.: 45; AR 17

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Opinion on cyclomethicone (D4 / D5)
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In Vitro Data on Metabolism
Guideline:
Test system:
Test substance:
Batch:
Dose levels:
Controls:
GLP statement:

/
Human liver microsomes (from a pool of 15 donors); Rat liver
microsomes (from untreated and PB induced Sprague Dawley rats)
14
C-D4, specific activity 20.6 Ci/mol
14
C-D4, lot 990316, radiochemical purity 99.67%.
3 M and 5 M D4, 49.5 nCi / incubation
Incubation conditions: 0-60 min (and several amounts of microsomal
protein)
No substrate and no protein samples
/

Incubations with 14C-octamethyltetracyclosiloxane were carried out to assess species
differences and investigate the role of human liver microsomal enzymes in its in vitro
metabolism.
Results
14
C-D4 was converted by liver microsomes from the phenobarbital-treated rats to at least
eight metabolites, designated M1 through M8, based on their HPLC retention times, but not
further characterised. M8 was the major metabolite formed in incubations with human liver
microsomes and also in liver microsomes from saline-treated rats, suggesting a similarity in
the metabolism of D4 for rats and humans. The conversion of D4 to M8 did not exceed 10%,
yet, the formation of M8 was not proportional to protein concentration or incubation time.
Results of an experiment to assess 14C-D4 binding to human liver microsomes indicated that
this was not due to the binding of 14C-D4 and its metabolite(s) to the microsomal protein.
The observation that incubations with microsomes from phenobarbital-treated rats caused
extensive metabolism of D4 suggested also that microsomal metabolism of D4 in the
uninduced system is a complex blend of enzyme action and inhibition.
Ref. 46
Guideline:
Test system:
Test substance:
Dose levels:
GLP statement:

/
Human liver microsomes (from a pool of 7 individuals); Rat liver
microsomes (from MC and PB induced rats)
14
C-D4, specific activity 47 Ci/mol, lot #970310-4, and D4 LL024S10,
purity 96%
0.032 µM to 2.9 µM
/

The study was conducted to evaluate the ability of D4 to inhibit the major cytochrome P450
(CYP) enzymes in human and rat liver microsomes.
Results: The study showed D4 to be a non-competitive inhibitor of human CYP2B6, CYP2D6
and CYP3A4/5, a competitive inhibitor of human CYP1A2, and either a competitive or noncompetitive inhibitor of CYP2C19. D4 appeared to have no capacity to inhibit rat CYP1A2 or
human CYP2A6, CYP2C9 and CYP4A9/11 activity. Because D4 is an activator, not an
inhibitor of human CYP2E1, D4 has little or no capacity to function as a metabolismdependent inhibitor of any of the CYP enzymes examined with the possible exception of rat
CYP1A1/2 and human CYP3A4/5.
Ref. 48
Conclusion
Based on results of two in vitro studies with human liver microsomes (Refs. 46, 48), it was
concluded that 14C-D4 is primarily metabolized to metabolite M8, and that CYP2B6 and
CYP3A4 are largely responsible for its formation.
50

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Human data
Guideline:
Species/strain:
Group size:
Test substance:
Batch:
Test formulation:
Dose level:
Control:
GLP statement:

/
Human volunteers
8 males and 4 females aged 25 to 49 years
D4
14
C-D4, specific activity was 2.0 mCi/mmole
D4, lot LL084732, purity 99.8% (GC-MS)
14
C-D4, lot 921217, radiochemical purity 99.03%
Air containing 10 ppm D4 (122 µg/l)
10 ppm D4 for 1 hour, two exposures separated by one week
Three months later the exposure was repeated.
Blood samples after D4 exposure and at 1, 6 and 24 hours postdose
double-blind cross over study
/

The respiratory intake and uptake of D4 were measured in 12 healthy volunteers (25-49
years; 8 males and 4 females) on two occasions. Subjects inhaled 10 ppm D4 (122
micrograms/liter) or air (control) during a 1h exposure via a mouthpiece in a double-blind,
randomized fashion. Inspiratory and expiratory D4 concentrations were continuously
measured. Exhaled air and plasma D4 levels were measured before, during, and after
exposures. Individual D4 uptakes were measured under steady-state conditions during
three rest periods (10, 20, and 10 min, respectively) alternating with two 10-min exercise
periods.
At the end of the 1h exposure to D4, the mean D4 concentration in the blood plasma was
56 ng/g of plasma. Symptoms and finding in pulmonary function tests were minimal and not
treatment related. No significant change in forced vital capacity (FVC), and FVC in 1 sec
(FVC1) was observed immediately after exposure or 24 h post-exposure for either the air or
D4 compared with the baseline measurements immediately prior to exposures.
Mean D4 intake was 137 ± 25 mg (SD) and the mean deposition efficiency was equivalent
to 0.74/(1 + 0.45 VE), where VE is the minute ventilation. No changes in lung function were
induced by the D4 vapour. Plasma measurements of D4 gave a mean peak value of 79 ± 5
ng/g (SEM) and indicated a rapid nonlinear blood clearance. A model was developed, using
lung volume and respiratory surface area estimates based on functional residual capacity
measurements, to determine the effective mass transfer coefficient for D4 (5.7 x 10(-5) cm/s
from lung air to blood). In additional eight subjects, a comparison of mouthpiece and nasal
breathing on D4 deposition, at resting ventilations, was made. Mean deposition was similar
for the two exposure protocols, averaging 12% after correction for exposure system losses.
Ref.: 40; AR 18
Assays were chosen to screen for immunotoxicity or a systemic inflammatory response.
Assessment of immunotoxicity included enumeration of peripheral lymphocyte subsets and
functional assays using peripheral blood mononuclear cells. Because in humans there is no
direct test for adjuvant effect of respiratory exposure, proinflammatory cytokines and acutephase reactants in peripheral blood, markers for a systemic inflammatory response, as
surrogate markers for adjuvancy were analyzed. These tests were repeated when the
volunteers were reexposed to D4 approximately 3 months after this initial exposure. Blood
was obtained prior to exposure, immediately after exposure, and 6 and 24 h postexposure.
In vivo cytokine production using a supersensitive ELISA for IL-6 in serum and serum levels
of acute phase reactants, serum amyloid A (SSA) and C-reactive protein (CRP) were
measured. The erythrocyte sedimentation rate and lipopolysaccharide-induced production of
TNFα was assessed.
The baseline values were 1.0 pg/ml for IL-6, 24 mg/ml for SAA, 0.28 mg/dl for CRP, and
5.4 mm/h for ESR. At no time point was there a significant “treatment effect”. At every time
point after air or D4 exposure, there was no difference between groups in the total white
blood cell count or in the percentage of lymphocytes (determined by complete blood count
51

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and differential, data). Lymphocyte subsets were measured by flow cytofluorometry. The
percentages of CD41, CD81, CD191, and CD561/CD161 lymphocytes were unaffected by
exposure to D4. Functional Studies of peripheral blood mononuclear cells (PBMCs) have
shown that there was no “treatment effect” seen in phytohemagglutinin (PHA)-induced
proliferation. There was also no significant difference in allogeneic stimulation immediately
post-exposure. The data have shown that there was no significant difference in NK cell
cytotoxicity either immediately or 24 h following exposure. The production of IL-2,
interferon γ, and TNFα measured by ELISA in the supernatant from PBMCs stimulated for 48
h with PHA was measured. The only statistically significant effect of exposure to D4 (p
<0.05) was for IL-2 production 6 h post-exposure. The PHA-induced IL-2 production was 28
U/ml for air and 18 U/ml for D4 exposure (p for treatment effect = 0.045). This effect was
not seen immediately after exposure or 24 h post-exposure TNFα production by diluted
whole blood was not different in the two exposure groups.
Rechallenge several months later (double blind, crossover protocol as with the initial study),
no “treatment” effect of D4 occurred, i.e., no difference between the second D4 exposure
and the second air exposure, in terms of pulmonary function tests, white blood cell count,
percentages lymphocytes/neutrophils/monocytes in the differential, percentage of
lymphocytes staining for CD4, CD8, CD19, or CD56/CD16, ESR, serum levels of IL-6, SAA,
or CRP, proliferative response to PHA or alloantigens, NK cell-mediated cytotoxicity, or
production of IL-2 or interferon g after PHA stimulation. In particular, a decrease in IL-2
production at the 6-h point after D4 exposure was not seen. The only statistically significant
effect (p <0.05) was seen for PHA-induced TNFa production at the 24-h time point. With
PHA stimulation of PBMCs, TNFα production for the 24-h post-exposure time point was 5958
pg/ml for the air-exposed group and 10,081 pg/ml for the D4-exposed group (treatment
effect p = 0.018). Immediately and 6 h post-exposure there was no difference. In addition,
with the whole blood assay there was no significant difference in LPS-induced TNFα
production at that same time point. LPS induced TNFα production was 948 pg/ml for air
versus 1117 pg/ml for D4 (treatment effect p = 0.51). There was no significant effect of D4
on total protein at 6 h and aspartate transaminase post-exposure at other times in the first
exposure or at any time in the second set of exposures.
Conclusion
Most individuals had minimal symptoms. However, the total symptom score was similar for
D4 and air exposures. These are the first human data describing the intake and absorption
of D4.
Ref.: 40, 41; AR 18
Guideline:
Species/strain:
Group size:
Test substance:
Batch:
Test formulation:
Dose level:
GLP statement:

/
Human, 6 male volunteers, 24 to 52 years old.
see study #8464 (Ref 44) and Study 8496 (Ref)
D4
D4, Lot number LL024S10, purity 99.75% by GC-MS.
14
C-D4, lot number 971210 radiochemical purity 98.91%, specific
activity 49.39 mCi/mmol.
D4 vapour and 14C-D4 diluted with unlabeled D4 vapour.
10 ppm 14C-D4 with intermittent exercise, for one hour.
/

The purpose of this study in humans was to increase the analytical sensitivity of D4
measurements and to quantify D4 hydrolysis products in blood and urine. Blood samples
were obtained 5 minutes after an exercise period. Following exposure to D4, volunteers
were switched to room air for a 20-minute wash-out period. A 24-hour urine sample was
then collected. Blood and exhaled air were also collected 3 and 6 hours post exposure.
Results
The mean respiratory intake increased to 154±39 mg and the uptake to 19±6 mg. A rapid
respiratory elimination of 28% of the absorbed dose was observed. Plasma measurements
52

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immediately post exposure revealed a mean peak value of 115±50 for D4 in ng/g and
161±53 in 14C activity equivalents, respectively, and indicated a rapid non-linear clearance
from plasma. Similar relationships were found in blood. Metabolites were far more
persistent in blood and plasma than parent D4 and were still present at 24 hours postexposure. Approximately 25-30 % of the D4 uptake was found in urine when the 14C activity
of the metabolites was expressed in D4 equivalents. Human urine chromatograms were
qualitatively very similar to those of the rat. One metabolite in man, tentatively identified as
trimethyldisiloxane-1,3,3-triol, is not detected in rat.
Ref.: 47
Pharmacokinetic modelling
A physiologically based pharmacokinetic (PBPK) model to describe the tissue dosimetry,
plasma concentration and clearance in the rat following inhalation, dermal, oral and i.v.
exposure indicated that the pharmacokinetics of D4 delivered by the inhalation or dermal
routes were similar, and that it is different from the i.v. or oral delivery routes.
Recent toxicokinetic and pharmacokinetic modelling studies [65, 66] investigated the
question how the exposure route (inhalation, dermal and oral) affects bioavailability of D4
and hence the biologically relevant internal dose: when absorbed through the lungs, D4
enters the arterial systemic circulation where it is distributed throughout the body to
potentially all organ systems. When absorbed by the dermal route, D4 enters the venous
circulation, which moves directly to the heart and lungs where the majority of the D4 is
then eliminated via exhaled air and therefore unavailable systemically. A series of studies
(described above) were conducted and a PBPK model constructed to evaluate the
magnitude of the difference. D4 has been shown to have a very low blood:air partition
coefficient. Consistent with this low blood:air partition coefficient, exhalation is the major
route of elimination following dermal absorption of D4 with 80% or more of D4 that reached
the systemic circulation being eliminated by exhalation within 24 hours [67 or AR 13]. This
model also indicates that the percent of a dermally applied dose of D4 that penetrates into
the systemic circulation is about 0.3% or less.
In a recent publication [78], it was emphasized that the oral route of exposure is an
inappropriate route of exposure for the purposes of risk characterization and, therefore, risk
assessment. The reason for this is that D4 appears to enter the blood in a different form
following oral administration from that for the inhalation or dermal routes of exposure. For
the oral route, D4 appears to be delivered via the lymphatics with the lipid core of
chylomicrons and other lipoproteins. Given the route-specific nature of D4
pharmacokinetics, oral pharmacokinetic data collected is not as useful in understanding the
bioavailability or tissue kinetics of D4. The oral pharmacokinetic data therefore, may not be
practical for safety assessments and can lead to misleading or erroneous conclusions.
Ref.: 65, 66, 67 (AR 13), 78
3.3.10.

Photo-induced toxicity

No data was submitted.
Siloxanes (such as D4) contain only methyl groups, which have no double bonds and do not
absorb ultra violet radiation. Consequently, no phototoxicity studies have been performed.
3.3.11.

Immunotoxicity

Studies in rats and humans have been conducted with different routes of application in
order to examine the potential effects of D4 on the immune system.

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
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Male and female Fischer 344 rats were used in a series of studies with gavage
administration of D4: Immunotoxicity was assessed by splenocyte phenotyping, peripheral
blood phenotyping, spleen IgM antibody response to the T-dependent antigen sRBC, serum
IgM antibody titres, mixed leukocyte response to Long Evans and Brown Norway rat spleen
cells, mixed leukocyte response, clearance of sRBC by the reticulo-endothelial system and
natural killer cell activity. These biological parameters were measured one day after 28 days
of oral gavage doses of 10, 30, 100 or 300 mg/kg D4 in corn oil. The studies [Ref. 54]
showed that D4 does not cause immune suppression in male or female Fischer 344 rats.
An in vitro study with cultured human peripheral blood mononuclear cells showed that in the
absence of serum, D4 was toxic to these cells, inhibiting proliferation induced by
phytohaemaglutinin at concentrations greater than 10 µM/ml. This inhibitory effect was
completely reversed by the addition of small amounts of serum or plasma to the serum-free
medium. The serum factors responsible for this protection are lipoproteins. However, this
inhibitory effect is irrelevant systemically since high levels of phospholipids in plasma would
neutralise such effects. Nevertheless, culturing human peripheral blood mononuclear cells
and D4 with or without serum was not associated with the production of TNFα [Ref 55].
Human volunteers were exposed to an oral dose of 12 mg D4/day in corn oil for 14 days in
a double blind, placebo-controlled crossover study design. Assays for immunotoxicity
included enumeration of peripheral lymphocyte subsets and functional assays using
peripheral blood mononuclear cells. Pro-inflammatory cytokines and acute phase reactants
in peripheral blood were used as surrogate markers for adjuvancy. No immunotoxic or proinflammatory adjuvant effect of D4 ingestion was found [Ref. 56].
Human volunteers were also exposed by inhalation to 10 ppm D4 for one hour on two
occasions each separated by one week. The exposure was repeated 3 months later.
Assessment of immunotoxicity was as described above [Ref. 56]. No immunological effect of
respiratory exposure to D4 was found. Furthermore, no evidence of sensitisation was
detected in another study [Ref. 41], described in more detail in section 3.3.9.
3.3.12.

Special studies

Rat studies to elucidate the hepatomegaly
Guideline:
Species/strain:
Group size:
Test substance:
Batch:
Test formulation:
Dose level:
Vehicle/Control:

GLP statement:

/
Rat, Fischer 344, male and female
24/sex/group except for positive controls (7/sex).
D4
D4, lot LL024S10, purity 99.8% (GC-MS)
D4 vapour/air mixture
Whole body; 70 or 700 ppm; 6h/day, 5 days/week; 4 weeks
Interim sacrifices exposure day 3, 7, 14, 21 28 and post exposure days
7, 14
Positive controls Phenobarbital (40mg/ml in 0.9% saline), 80 mg/kg i.p.
for 2 to 4 consecutive days prior to sacrifice.
Negative and positive controls exposed to air, 6h/day, 5 days/week, 4
weeks
/

Two identically designed studies to demonstrate the effects of D4 on liver size and enzyme
induction in the rat.
Clinical signs were monitored daily, body weight recorded on day 1, then every 7 days
throughout the study. Following sacrifice, liver and brain tissue were removed (brain was
not used in this study). Liver tissue was placed in homogenisation buffer for preparation of
hepatic microsomes. CYP and NADPH-cytochrome c reductase activities were determined.

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Results
No effects on clinical signs, mortality or body weights were noted. There was a significant
increase in liver weight (17%) at 700 ppm compared with controls (trend also at 70 ppm).
Liver size decreased to within control values during the 14-day post-exposure (recovery)
period.
There was a small increase in total hepatic CYP enzymes and a modest increase in NADPHcytochrome c reductase activity. A slight induction in ethoxyresorufin O-deethylase (EROD)
activity and in CYP3A1 immunoreactive protein was detected. A large increase in pentoxyresorufin O-depentylase (PROD) activity correlated with an increase in CYP2B1/2 protein
levels. A modest induction of microsomal epoxide hydrolase (mEH) mRNA, immunoreactive
protein, and activity was observed. (Dose-dependent and partly strong induction of hepatic
CYP enzymes i.e. ethoxyresorufin O-deethylase, pentoxyresorufin O-depentylase, 6ßtestosterone-hydroxylase, p-nitrophenol hydroxylase and P450 proteins (total P450, CYP
2B1/2, CYP 3A1/2, CYP 2E1) at 70 and 700 ppm; induction of hepatic phase-II conjugation
enzymes (UDP-glucu-ronosyltransferase towards chloramphenicol at 70 ppm, mEH in 70
and 700 ppm males and females) and increase of mEH mRNA protein in 70 ppm females
and 700 ppm males and females; dramatic and dose-dependent decrease in lung PROD
activity in 70 and 700 ppm males and females.)
The magnitude of this induction was nearly identical to that observed in the phenobarbitaltreated positive control animals.
Ref.: 57, 58
In this peer reviewed publication, a similar response was obtained on liver weight and CYP
enzyme activity in Sprague Dawley rats treated with D4 in corn oil by oral gavage at dose
levels of 1, 5, 20 or 100 mg/kg body weight for 4 consecutive days. Negative controls
received corn oil, positive controls received 50 mg/kg phenobarbital in phosphate buffer by
intraperitoneal injection for 4 days.
Ref.: 59
Another study examined CYP induction in female young, mature and pregnant Sprague
Dawley rats treated with D4 by oral gavage at dose levels of 0, 5, 20 or 100 mg/kg body
weight for 8 consecutive days. The peer reviewed publication reports dose and agedependent increases in CYP2B and CYP3A isoforms: the increases were significant at doses
of 20 mg/kg bw and higher, and there was a 20% increase in the liver to body weight ratio
in mature rats treated with 100 mg/kg D4. No histological examination was conducted. At
100 mg/kg-bw/day, additional effects included decreased foetal body weights and liver
weight / body weight ratio in foetuses.
Ref.: AR 19
Guideline:
Species/strain:
Group size:
Test substance:
Batch:
Test formulation:
Dose level:
Vehicle/Control:
GLP statement:

/
Rat, Fischer 344, female
10 per group
D4
D4, lot LL024S10, purity >99% (GC-MS)
D4 vapour
0, 1, 7, 30, 70, 150, 300, 500, 700 or 900 ppm; whole body; 6h/day for
5 days
Positive controls Phenobarbital in the drinking water at 500 ppm
Negative controls received filtered room air
in compliance

This was a metabolism study to investigate the effects of D4 on hepatic microsomal enzyme
induction in rats. Within each group, three subgroups were used for liver biochemical
analyses and two subgroups used for determining D4 in blood, fat and liver.
Results

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Opinion on cyclomethicone (D4 / D5)
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There were no effects on body weight. A dose-related increase in liver weight occurred. The
liver-to-plasma D4 ratio remained constant over the dose range.
The lowest dose level to induce significant hepatomegaly was 150 ppm. D4 content in fat,
liver and plasma increased proportionally with increasing exposure concentrations. A dosedependent increase occurred in PROD activity and in CYP2B1/2 proteins with a maximum
response at 500 ppm D4. These findings are consistent with those reported for
phenobarbital and confirm that D4 is a qualitative “phenobarbital-like” inducer of rat hepatic
cytochrome P450 enzymes.
A NOEL of 70 ppm D4 is based on enzyme induction in female rats.
Ref.: 60
Guideline:
Species/strain:
Group size:
Test substance:
Batch:
Test formulation:
Dose level:
Vehicle/Control:
GLP statement:

/
Rat, Sprague-Dawley, male
10 per group
D4
Lot number LL108831, purity approx. 98%
D4 in 0.5% aqueous methylcellulose
Two groups received 1600 mg/kg/day D4 oral gavage for 14 consecutive
days
Negative controls (two groups of 10 males) vehicle only at 4 ml/kg
in compliance

This was a morphometric study and DNA analysis designed to define the mechanism that
caused the hepatomegaly in rats exposed to D4. The animals were examined daily for
clinical signs and weighed weekly. At termination, rats were euthanised by perfusion fixation
accomplished by flushing the vascular system with glutaraldehyde/formaldehyde solution.
Livers were collected for light and electron microscopy and for determination of DNA
concentration.
Results
No deaths occurred and no clinical signs of toxicity were observed. No differences in body
weights were noted.
Morphometric analysis revealed no significant difference in the number of cells per given
volume of liver between control and treated rats. However, there was a significant increase
in the total number of hepatocytes in the treated rat liver demonstrating that D4 causes
hepatocellular hyperplasia. The mean hepatocyte profile diameter in the three lobular zones
did not differ significantly between treated and control rats.
No significant difference in DNA values between treated and control rats was detected.
Further, as the DNA content of the liver was similar for treated and control rats, this
suggests that the same number of nuclei was present in each sample of liver (control vs.
treated). The results of these studies indicate that hepatomegaly is due in part to
hepatocellular hyperplasia.
Ref.: 61, 62, 63
Additional studies by McKim et al. compared D4 and phenobarbital treatment in F344
female rats. Both compounds produced hepatomegaly, transient hepatic hyperplasia and
sustained hepatic hypertrophy. At 700 ppm D4 (6 hours/day, 5 days/week), the
hyperplastic effect was greatest at day 6 and was still present at day 13 to a small extent,
but had declined to normal by day 27. This pattern of transient hyperplasia followed by
sustained hypertrophy leading to hepatomegaly is consistent with the pattern observed for
phenobarbital. Data from this study, namely hepatic CYP2B1/2 activity, plasma and tissue
D4 concentrations, were also used to develop a pharmacokinetic model that describes the
dose-response curves for enzyme induction (Ref.: AR23).
Ref.: 64, AR23

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
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Comment
Administration of D4 by oral or inhalation routes to rats causes hepatomegaly as a result of
hepatocellular hyperplasia and hypertrophy. The enzyme expression profile observed in rats
following exposure to D4 is similar to that observed following exposure to phenobarbital.
Therefore, D4 may be considered a “phenobarbital-like” inducer in rat liver. Interestingly,
and inspite of being ‘phenobarbital-like’, chronic administration of D4 to F344 rats in the
carcinogenicity study did not induce hepatomegaly or any hepatic lesions of relevance,
including tumours, even at the high dose of 700 ppm (see Section 3.3.7.). It is clear that
not all chemicals that induce hepatomegaly are tumorigenic in lifetime bioassays.
Studies to elucidate estrogenic and antiestrogenic effects of D4 in rats and mice
Guideline:
Species/strain:
Group size:
Test substance:
Test formulation:
Dose level:
Vehicle/Control:
Positive Controls:
GLP statement:

Prior to, but in line with OECD 440
Rat, immature female Sprague-Dawley and Fischer 344
12 per group
D4
D4 in sesame oil
0, 50, 100, 250, 500 and 1000 mg/kg/day D4 by daily oral gavage for 3
consecutive days in uterotrophic assays
received sesame oil by gavage
1, 3, 10 or 30 µg ethinylestradiol (EE), and antiestrogen ICI182,780
plus ethinyl estradiol administered at 3 mg/kg and 1-30 µg/kg EE;
DES-dipropionate at 0.5, 1.5, 5 and 15 g/kg per day
in compliance

Results
Decreased body weight gain was seen at 250 mg/kg D4 and above in both strains of rats.
Increased liver weights at 100 mg/kg D4 (Fischer 344) or 250 mg/kg D4 (Sprague-Dawley)
and above. Increased uterus weight at 250 mg/kg D4 and above (both strains). D4 inhibited
uterotrophic response of EE in both strains at 500 mg/kg, showing a weak antiestrogenic
activity. At the 50 % of maximal response D4 was approx. 1.2 to 25 million times less
potent than EE or DES-DP in Sprague-Dawley and Fischer 344 rats, respectively. Decreased
body weight gain was observed at 250 mg/kg D4 and above. Increased liver weights were
seen at 100 mg/kg D4 (Fischer 344) or 250 mg/kg D4 (Sprague-Dawley) and above.
Increased uterus weight occurred at 250 mg/kg D4 and above (both strains).
Conclusion
D4 inhibited uterotrophic response of EE in both strains at 500 mg/kg indicative of a weak
antiestrogenic activity. At the 50 % of maximal response D4 was approx. 1.2 to 25 million
times less potent than ethinyl estradiol or diethylstilbestrol diproprionate in Sprague-Dawley
and Fischer 344 rats, respectively.
Ref.: 69; AR 20
Guideline:
Species/strain:
Group size:
Test substance:
Test formulation:
Dose level:

Vehicle/Control:

/
female estrogen receptor knockout (ERKO) mice and wild type mice
(129/J/C57BL/6J) and female B6C3F1 mice5 per group (uterotrophic); 8 per group (serum hormones)
D4
D4 in corn oil
a) uterotrophic assay: 0, 50, 100, 250, 500 and 1000 mg/kg/day D4 by
daily oral gavage for 3 consecutive days; sacrificed 24 h later
b) serum hormone: level: 1 to 1000 mg/kg/day D4 by daily oral gavage
for 7 consecutive days; sacrificed 24 h later
Negative controls received corn oil

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
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Positive Controls:
GLP statement:

estradiol (E2) 10 µg/kg by s.c., and antiestrogen ICI 182,780 at 20
mg/kg 30 min given s.c. prior before to dosing with D4 or estradiol
/

Results
Uterine weight was significantly increased by 250 to 1000 mg/kg D4 administered orally.
Uterine peroxidase levels (a marker for estrogenic activity) were also significantly increased
in D4 exposed mice. Pretreating mice with ICI 182,780 completely blocked D4-induced
increase in uterine weight. Further, ovariectomized estrogen receptor-knockout mice showed
no increase in uterine weights when exposed to D4 or estradiol. These uterotrophic effects of
D4 were ablated by pre-treatment with ICI 182,780, an estrogenic receptor (ER) antagonist.
Ovariectomised αER KO mice showed no increases in uterine weights when treated with D4.
Studies with adrenalectomized mice showed that decreased serum estradiol levels, which
were decreased upon oral administration of D4, were not due to elevated serum
corticosterone levels.
Conclusion
The data indicate that D4 has weak estrogenic activity, and these effects are mediated
through estrogen receptor (ER), probably by direct receptor binding via ERα. The data
indicate that the stimulatory effect of D4 on the mouse uterus is not related to estradiol
activity.
Ref.: 70
Studies to investigate effects of D4 on LH surge and reproductive hormone levels
in rats
Guideline:
Species/strain:
Group size:
Test substance:
Test formulation:
Dose level:
Vehicle/Control:
GLP statement:

/
Rat, ovariectomized female Sprague-Dawley; three days prior to
inhalation exposure, each female received a surgical implant of silastic
tubing containing 17ß-estradiol
10 per group
D4, Lot LL084732, 99.78% pure
D4 vapour (in air)
700 and 900 ppm D4 as a single whole body exposure for 6 hours
negative controls received filtered air
in compliance

The purpose of this study was to evaluate the potential of D4 to affect preovulatory
luteinizing hormone (LH) surge in ovariectomized rats. Blood samples were collected for LH,
prolactin and estradiol and/or estrone analysis after 6 hours exposure to D4 (at end of
exposure), or 2, 4, 6 or 8 hours post exposure.
Results and Conclusion
Group mean LH levels in ovariectomized females treated with estradiol via a subcutaneous
implant were similar to the control group mean following a single six-hour D4 exposure at
700 or 900 ppm. However, several animals in the 700 and 900 ppm exposure groups had
reduced LH levels (< 7 ng/ml) at the peak time of 6:00 p.m. relative to the control group.
Because the LH surge is required for ovulation to occur, these results suggest that the
reduced fertility rate observed in a previous study (Dow Corning Report No. 1999-I000047049) in which rats were exposed to D4 at 700 ppm on the day of proestrus may have
been the result of a reduction in peak serum LH levels.
Ref.: 74
Guideline:
Species/strain:

/
Rat, female Sprague-Dawley (13 weeks old)
58

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

Group size:
Test substance:
Test formulation:
Dose level:
Exposure:

Vehicle/Control:
GLP statement:

30 per group (Phase I); 20 per group (Phase II)
D4, Lot LL0024S10, 99.6% pure
D4 vapour (in air)
700 and 900 ppm D4
Phase I: Cannulated rats received 6 hours/day exposure to D4 for 3
days on diestrus –1, diestrus –2 and proestrus.
Phase II: non-cannulated rats exposed 6h/day to D4 for 2
consecutive days of diestrus and 2.5 h on proestrus
negative controls received filtered air
no

This study assessed the ability of D4 to attenuate the preovulatory LH surge, and to assess
the ability of D4 to block or delay ovulation, and to evaluate the levels of other reproductive
hormones in D4 exposed rats. Prior to treatment, estrous cycle was staged for 10-12 days.
Blood collected from Phase I rats on the day of proestrus at 2, 4, 6, 8 and 10 p.m. for
plasma LH and prolactin measurements. Following necrospsy on morning of next estrus,
blood was collected for FSH, estradiol, estrone and progesterone measurements. Brain,
uterus and ovary weights recorded and ovaries evaluated histopathologically. Phase II rats
blood samples were taken for FSH, estradiol, estrone and progesterone measurements.
Results and Conclusion: D4 exposure resulted in significant reductions of proestrus LH levels
in 900 ppm group at 4, 6 and 8 p.m., A smaller effect was seen at 700 ppm. As a
consequence, only 42% and 31% of rats at 700 or 900 ppm ovulated compared to 79% in
the controls. On the morning of estrus, higher levels of estradiol were found in rats at 700
or 900 ppm D4 relative to controls, indicating failure of mature follicles to ovulate.
Therefore, high exposure to D4 attenuates the preovulatory LH surge and significantly
decreases the proportion of females that ovulate.
Ref.: 75; AR 21
The mechanism for delayed ovulation status resulting in reduced fertility has been studied.
The observed changes were shown to be reversible (Ref. 32, 33). Other studies have shown
that D4 has very weak estrogenic and anti-estrogenic activity in vitro and in a Rat
Uterotrophic Assay in both immature Sprague Dawley and F344 rats (Ref. 69; AR 21).
Rather than a direct estrogen receptor (ER)-mediated mechanism (of very low potency), an
indirect mode of action appears to be more relevant for explaining the reproductive toxicity
and carcinogenicity of D4 observed at high doses: There are data in rats indicating that D4
can cause a delay or blockage of the luteinizing hormone (LH) surge necessary for optimal
timing of ovulation (Ref. 74). Support for a role of LH was obtained from a study of estrous
cycle staged female Sprague Dawley rats exposed to 700 or 900 ppm D4 for 6h/day for 3
days, i.e. on diestrus 1, diestrus 2, and pro-oestrus. Measurement of LH on the day of proestrus at 2, 4, 6, 8 and 10 p.m. showed a significant reduction of LH levels at 4, 6 and 8
p.m. which correlated with blocked ovulation (Ref. 75). The majority of reproduction
findings in the two-generation study are also consistent with a long-term suppression of LH
release.
While it is possible that D4 can affect the secretion of LH in female F344 rats in a manner
similar to that observed for SD rats (Ref. 75, AR 21), it is also possible that the mode of
action for the cystic endometrial hyperplasia and endometrial adenomas observed in the
combined chronic/carcinogenicity study is by effects on prolactin through interaction with
the dopamine receptor in the pituitary. This view is supported by as yet unpublished studies
in vitro and in vivo indicating that D4 can inhibit prolactin release from the pituitary by
acting as a dopamine agonist (Ref. AR5). However, at present there is insufficient data for
this suggested neuroendocrine mode of action in rats to preclude a relevance for humans.
The absence of genotoxic potential supports the view that tumour formation is due to
threshold effects.

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

3.3.13.

References for D4 (section 3.3)

Submission 1
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13
14.
15.
16.
17.
18.
19.
20.

21.

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Dow Corning Corporation (1994), RCC Group. Report No. 1994-I0000-39679,
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Dow Corning Corporation (1990). A 14-day subchronic oral gavage study with D4 in
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Dow Corning Corporation (1988). Feasibility studies to determine the palatability of D4
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Dow Corning Corporation (1992). A 14-day oral gavage study of D4 in female rabbits.
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Bayer AG. Subakute toxikologische Untersuchungen an Kaninchen. Report No. 16886,
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60

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

22.
23.

24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
36.

37.
38.

39.

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110].
Global Silicone Producers Association, International Research and Development
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Global Silicone Producers Association, International Research and Development
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665-004, December 16, 1993. [IUCLID Ref. 107].
Global Silicone Producers Association, International Research and Development
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Dow Corning Corporation, WIL Research Laboratories, Inc. (1996) An inhalation range
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Dow Corning Corporation, WIL Research Laboratories, Inc. (1998). An inhalation
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Dow Corning Corporation (1998) An oral gavage study to compare the absorption
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61

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

40.
41.
42.

43.

44.
45.
46.
47.
48.
49.
50.
51.
52.
53.
54.
55.
56.

57.
58.

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SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

59.
60.
61.
62.
63.
64.

65.
66.
67.

68.
69.
70.
71.
72.
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74.
75.
76.
77.
78.

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SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

Submission II, November 2004
79.

Dow Corning Cooperation (2004). 24-month combined chronic toxicity and
oncogenicity whole body vapor inhalation study of octamethylcyclotetrasiloxane (D4)
in Fischer 344 rats. Report no. 2004-10000-54091.

Submission III, November 2006
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Applications. HES Study n° 10278-108. Dow Corning Corporation, Auburn, MI 48611.
7 November 2006
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in 2006)
SEHC, CES, SIAJ. Decamethylcyclopentasiloxane (D5): A White Paper on Health
Research Findings. June 2005
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frequency are they used in cosmetic products? Norwegian Food Safety Authority. Note
2006-11-19

Additional References (AR)
AR1 Ulman K, Neun D. and Tan-Sien-Hee L. Silicones for topical pharmaceuticals.
Pharmaceutical Formulation & Quality, April/May 2005, p.136-142.
AR2 Schipp AM, Van Landingham CV and Meeks G (2000) Estimation of margins of
exposure: a preliminary risk assessment for octamethylcyclosiloxane (D4) based on
reproductive toxicity studies in Sprague-Dawley rats. [Abstract] Toxicologist 54 (1),
108.
AR3 Burns-Naas LA, Meeks RG, Kolesar GB, Mast RW, Elwell MR, Hardisty JF, Thevenaz P
(2002) Inhalation toxicology of octamethylcylotetrasiloxane (D4) following a 3-month
nose-only exposure in Fisher 344 rats. Int J Toxicol 21, 39-53
AR4 Plotzke KP, Jean PA, Crissman JW, Lee KM, Meeks RG, Chronic toxicity and oncogenicity study of octamethylcyclotetrasiloxane (D4) in Fisher 344 rats. Abstract no
1507; Proceedings 44nd Annual Meeting of Society of Toxicology. New Orleans 2005.
AR5 Jean PA, McCracken KA, Arthurton JA, Plotzke KP Investigation of octamethylcyclotetrasiloxane (D4) and decamethylcyclopentasiloxane (D5) as dopamine D2-receptor
agonists. Abstract no 1812; Proceedings 44th Annual Meeting of Society of Toxicology.
New Orleans 2005.
AR6 Dow Corning Technical Report 1999-I0000-46358. Estimation of margin of exposure:
a preliminary risk assessment for octamethylcyclotetrasiloxane (D4) based on
reproductive toxicity studies.
AR7 ECB 2000. IUCLID Dataset octamethylcyclotetrasiloxane. 18 Feb. 2000.
http://ecb.jrc.ec.europa.eu/iuclid-datasheet/556672.pdf
AR8 Ministers of the Environment and of Health, Canada. Screening Assessment for
Octamethylcyclotetrasiloxane (D4). November 2008
AR9 Ministers of the Environment and of Health, Canada. Screening Assessment for
Decamethylcyclopentasiloxane (D5). November 2008
AR10 OEHHA (2007). Toxicity Data Review: Decamethylcyclopentasiloxane (D5). September
13,
2007.
Available
at:
www.oehha.ca.gov/multimedia/biomon/pdf/1208cyclosiloxanes.pdf
AR11 Jovanovich ML, McMahon JM, McNett DA, Tobin JM, Plotzke KP (2008) In vitro and In
vivo percutaneous absorption of 14C-octamethylcyclotetrasiloxane (14C-D4) and 14Cdeca-methylcyclopentasiloxane (14C-D5). Regulatory Toxicol Pharmacol 50: 239–248
AR12 Zareba G, Gelein R, Morrow PE, Utell MJ (2002) Percutaneous absorption studies of
octamethylcyclotetrasiloxane using the human skin/nude mouse model. Skin
Pharmacol. Appl. Skin Physiol. 15, 184-194

SCCS/1241/10
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AR13 Reddy M.B., Looney RJ, Utell MJ, Plotzke KP, Andersen ME (2007). Modeling of human
dermal absorption of octamethylcyclotetrasiloxane (D4) and decamethylcyclopentasiloxane (D5). Toxicological Sciences 99(2), 422–431
AR14 Meeks RG, Stump DG, Siddiqui WH, Holson JF, Plotzke KP, Reynolds VL (2007). An
inhalation reproductive toxicity study of octamethylcyclotetrasiloxane (D4) in female
rats using multiple and single day exposure regimens. Reprod Toxicol.; 23(2):192-201
AR15 Siddiqui WH, Stump DG, Plotzke KP, Holson JF, Meeks RG (2007a) A two-generation
reproductive toxicity study of octamethylcyclotetrasiloxane (D4) in rats exposed by
whole-body vapor inhalation. Reprod Toxicol. 23(2):202-215
AR16 Plotzke KP, Crofoot SD, Ferdinandi ES, Beattie JG, Reitz RH, McNett DA, Meeks RG
(2000) Disposition of radioactivity in Fischer 344 rats after single and multiple
inhalation exposure to [14C]octamethylcyclotetrasiloxane ([14C]D4). Drug Metab
Dispos 28:192-204.
AR17 Varaprath S, Salyers KL, Plotzke KP, Navanati S. (1999) Identification of metabolites
of octamethylcyclotetrasiloxane (D4) in rat urine. Drug Metab Dispos 27: 1267-1273.
AR18 Utell MJ, Gelein R, Yu CP, Kenaga C, Geigel E, Torres A, Chalupa D, Gibb FR,
Speers DM, Mast RW, Morrow PE (1998) Quantitative exposure of humans to an
octamethyl-cyclotetrasiloxane (D4) vapor. Toxicol Sci. 44(2): 206-213. AR19 Falany
CN and Li G (2005) Effects of age and pregnancy on cytochrome P450 induction by
octamethyl-tetracyclosiloxane in female Sprague-Dawley rats. J Biochem Mol Toxicol.
19(2): 129-138. AR20 Quinn AL, Regan JM, Tobin JM, Marinik BJ, McMahon JM, McNett
DA, Sushynski CM, Crofoot SD, Jean PA, Plotzke KP (2007x) In vitro and in vivo
evaluation of the estrogenic, androgenic, and progestagenic potential of two cyclic
siloxanes. Toxicol Sci. 96(1): 145-153.
AR21 Quinn AL, Dalu A, Meeker LS, Jean PA, Meeks RG, Crissman JW, Gallavan RH Jr,
Plotzke KP (2007y) Effects of octamethylcyclotetrasiloxane (D4) on the luteinizing
hormone (LH) surge and levels of various reproductive hormones in female SpragueDawley rats. Reprod Toxicol. 23(4): 532-540.
AR22 Cosmetic Ingredient Review (2009) Amended Final Report of the Cosmetic Ingredient
Review Expert Panel of the Safety Assessment of Cyclomethicone, Cyclotetrasiloxane,
Cyclopentasiloxane, Cyclohexasiloxane, and Cycloheptasiloxane. Dezember 8, 2009;
AR23 Sarangapani R, Teeguarden J, Plotzke KP, McKim JM Jr, Andersen M (2002) Doseresponse modelling of cytochrome P 450 induction in rats by octamethylcyclotetrasiloxane. Toxicol Sci 67: 159-172.

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

3.4. Toxicological Evaluation of D5 (Decamethylcyclopentasiloxane;
Cyclopentasiloxane)
The description is largely based on SEHC, CES, SIAJ Decamethylcylopentasiloxane (D5): A
White paper on Health Research Findings (Ref.: 66). Since this document did only cover
studies and publications on D5 up to 2005, SCCS did take into consideration the available
open literature and more recent evolutions on health effects by other panels (Refs. AR12,
AR13, AR14).
3.4.1.

Acute toxicity

3.4.1.1.

Acute oral toxicity

Five male and five female Wistar rats survived a single oral gavage dose of 4800 mg D5/kg
bw with no overt signs of toxicity.
Ref.: 1
3.4.1.2.

Acute dermal toxicity

No study submitted
3.4.1.3.

Acute inhalation toxicity

Four groups of 5 male and 5 female Fischer 344 rats were exposed by whole body inhalation
to D5 during a single, continuous 4-hour period, followed by an observation period of 15
days. The achieved test atmosphere concentrations (sum of the aerosol and vapour phase)
were 4.64, 6.73, 9.82, and 15.37 mg D5/l of air (300, 434, 634, 1000 ppm, respectively).
Animals were observed for clinical signs, abnormal behaviour, mortality, body weight, body
weight gain, and food consumption during the 15-day observation period. All animals were
necropsied and all macroscopic abnormalities recorded at the end of the study. The food
consumption and mean body weights were decreased in animals exposed to concentrations
of 6.73 mg D5/l (434 ppm) and above but these effects were reversible during the
observation period. The clinical signs that were observed following exposure were of low
incidence. In animals dying spontaneously post exposure, the lungs were affected (red
lungs partly collapsed) while no macroscopic observations were recorded in any animals
necropsied at the scheduled sacrifice date. No animals died at the lowest exposure
concentration. At the intermediate exposure concentrations, four animals of each sex died.
All animals at the highest exposure concentration died during the exposure phase. The LC50
for both sexes was calculated to be 8.67 mg D5/1 (560 ppm).
Ref.: 2
Five male and 5 female Wistar rats survived a single four hour whole body vapour
exposure of >545 ppm of D5 with no overt signs of toxicity and no mortality.
Ref.: 3
3.4.2

Irritation and corrosivity

3.4.2.1.

Skin irritation

No special study submitted, but a subacute study with dermal application of D5 is relevant:
Six male and female New Zealand white rabbits were treated 6 hrs/day, 7 days/wk for 21
consecutive days with 1000 mg D5/kg bw under occlusive conditions. The skin was
abraded in one-half of the animals. Skin reactions were scored daily for signs of oedema and
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erythema. At necropsy, the heart, lungs, liver, kidneys, spleen, testes, epididymides, ovaries,
and urinary bladder were weighed and preserved. No clinical signs of toxicity were observed.
There was no effect on body weight, no mortality, no effect on organ weights, and no
treatment related gross pathology findings. No signs of skin irritation were observed.
Ref.: 16
3.4.2.2.

Mucous membrane irritation

Eye Irritation
A standard Draize test was performed using New Zealand White rabbits. A single treatment
with 100 µl of neat D5 liquid instilled into the conjunctival sac of the eye of 3 male and 3
female rabbits elicited no response. In this study, D5 was not an eye irritant.
Ref.: 13
Five rabbits (strain and sex not specified) received a single treatment of 500 µl of undiluted
D5 in the conjunctival sac. The eyes were stained with fluorescein at 24 hours and read for
irritation. There was no corneal injury following treatment with D5. Minor capillary injection of
the eyelids was noted. D5 was judged to be non-irritating.
Ref.: 14
Five hundred microliters of undiluted D5 were instilled into the conjunctival sac of six rabbits
(strain and sex not specified), 2 times/day for four consecutive days. No corneal injury or eye
irritation was observed among treated rabbits and controls receiving comparable amounts of
a saline solution.
Ref.: 15
3.4.3.

Skin sensitisation

Magnusson-Kligman Maximization test
Guinea pigs were pretreated intracutaneously with a 1% solution of D5 in paraffin oil and
epicutaneously with undiluted D5 using the "Maximization test" of Magnusson and Kligman.
Challenge with undiluted D5 and a 10% solution in paraffin oil did not elicit a hypersensitivity
skin response. The results of this study indicate that D5 and paraffin oil are not skin
sensitizers in the guinea pigs.
Ref.:18
HRIPT
In a Human Repeated Insult Patch Test (HRIPT) designed to assess skin irritation and
sensitization of D5 in humans, 28 males and 22 females were treated with a dermal
application of 0.05 ml test material three times/week for a total of 9 applications. The D5
was applied using an occlusive patch that remained in place for 24 hours. Skin was graded
for erythema, eschar, and oedema after the patch was removed. Twelve days after the ninth
application, the site was graded and 0.05 ml of D5 was applied to a new site and covered for
24 hours with an occlusive patch. The site was then re-graded for erythema, eschar, and
oedema immediately and at 24 and 48 hours after removal of the occlusive patch. No
dermal irritation or sensitization was reported following D5 exposure.
Ref.: 19
Comment
The SCCS considers HRIPT-studies as unethical.

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

3.4.4.

Dermal / percutaneous absorption

In Vitro
Excised split-thickness skin, ranging from 381-629 µm, from young adult Sprague-Dawley
rats was mounted on static Franz diffusion cells with 6% polyoxyethylene-20oleyl ether and
1% penicillin/streptomycin in saline solution as a receptor fluid. An initial screening to check
barrier integrity of the skin was accomplished by applying 970 µl of 3H2O (0.77 µCi) to the
surface of the skin for 20 minutes. Following administration of the 3H2O, the unabsorbed
material was removed from the skin; the receptor fluid was sampled and analysed for 3H at 60
minutes. Once the 3Η2O had been removed, 14C-D5 (6.4 mg/cm²) was applied to each skin
sample. Measurements were made of the 14C-labelled material that could be washed from
the skin, were associated with skin, or penetrated through the skin into the receptor fluid over
a 24-hour period. The washing procedure was performed using a 1% soap solution-moistened
gauze 3 times, followed by 3 washes with gauze moistened with 70% ethanol. The skin was
solubilised in 40% tetraethylammonium hydroxide. The cumulative penetration was calculated
based on the amount of radioactivity in the receptor fluid over the 24-hour sampling period.
The percentage of radioactivity found in the skin was 0.67% and 1.19% in males and females
respectively. The total absorbed (% radioactivity in the skin and receptor fluid) was 1.08% and
1.54% in males and females respectively. According to the applicant, these data need to be
evaluated cautiously due to unrecognized technical problems associated with working with
this material at the time this study was conducted. More reliable studies are reported below.
Ref.: 20
14

C-D5 was applied to semi-occluded human skin using a flow-through diffusion cell technique.
Human epidermis was prepared from intact abdominal skin. The epidermis was separated
from the dermis using a Padgett® dermatome. Skin disks from 6 donors were mounted in
replicate in the flow-through chambers. A physiological receptor fluid was pumped underneath
the skin samples and collected in a fraction collector. The barrier integrity of each piece of skin
was evaluated prior to dosing using 3H2O. Skin samples were evaluated on two separate
days. In experiment 1, skin samples from each of 3 donors were dosed with neat D5 and the
remaining 3 were dosed with a generic antiperspirant formulation containing D5. In
experiment 2, a second set of skin samples from the same 6 donors were dosed with the
other test article (i.e. antiperspirant or neat D5), and immediately after dosing, charcoal
baskets were placed above the skin and secured into a custom designed cap to capture any
volatilized material. At the end of 24 hours, the charcoal baskets were removed and
extracted, skin was washed and solubilised, and the receptor fluid was collected. The
radioactivity content in each sample was measured by liquid scintillation counting. The percent
dose absorbed was determined as the amount of radioactivity in the receptor fluid and the
amount left in the skin after washing and tape stripping. At the end of the assay, only 0.04%
± 0.007% of the applied dose of neat D5 was absorbed which was not significantly different
from that seen with formulated D5 (0.022% ± 0.005% of the applied dose). The percent of
applied dose recovered from all analysed samples for neat D5 was 91.45% ± 1.60% and for
D5 formulated in generic antiperspirant formulation was 98.05% ± 1.17%. The majority of
the dose was evaporated from the dosing site and was collected from the charcoal baskets.
Ref.: 21; AR1
In Vivo
14

C-D5 was applied to the dorsal surface of male and female Sprague-Dawley rats from which
the hair was clipped. The skin depot chamber (a Teflon® gasket attached to the dosing site
with cyanoacrylate glue, an activated charcoal trap, and a plastic cap with a hole to allow for
air circulation) was covered with a non-occlusive elastic wrap. At the termination of a 24-hour
exposure period, animals were removed from the metabolism cages and the exposure site
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was washed. Animals were rewrapped with a fresh nonocclusive bandage and returned to
metabolism cages for continued collection of samples. Animals were removed from the
metabolism cages 96 hours post-initial exposure, sacrificed, and the exposure site carefully
excised. The majority (about 85%) of the 14C-D5 volatilised from the skin surface. The dose
site, which was washed prior to excision at 96 hours, contained 0.35% of the administered
dose. Less than 1% of the dosed 14C was recovered in urine and carcass. There were trace
levels of 14C in faeces, CO2 traps, and tissues. Total radioactivity in excreta, carcass, and dose
site, which was considered to be the amount absorbed, was 0.80 ± 0.62% (n=11) with a
recovery of about 89%. According to the applicant, these data need to be evaluated cautiously
due to unrecognized technical problems associated with working with this material at the
time this study was conducted. The studies reported below were considered more reliable.
Ref.: 22
In another study, the percutaneous absorption of neat 14C-D5 was evaluated in Fischer 344
rats when applied topically at 10.9 mg/cm² of skin. Four animals per group were exposed
for 6 or 24 hours. Two control animals were euthanized at the 24-hour time point. In order
to differentiate expired air from 14C-D5 that escaped from the skin depot, an additional group
of four euthanized rats (i.e., no expired air) was included in the study design. An additional
24-hour exposure group was added to evaluate disposition of the residual D5 following a
soap and water wash (i.e., wash group). During exposure, rats were housed in Roth-style
metabolism cages to enable collection of urine, faeces, and expired or escaped volatiles
associated with D5. Dose sites were washed, charcoal baskets were replaced and the
animals were returned to the metabolism cages for continued collection of excreta and
expired volatiles for a total 168 hours. All rats were exposed in a semi-occluded manner
using an aluminium skin depot with a charcoal basket for collection of volatilized D5. At the
termination of exposure at 24 hours or at 168 hours post exposure, rats were euthanized by
CO2 asphyxiation, the charcoal baskets were removed and extracted, skin was washed, tape
stripped, excised, and solubilised in 35% tetraethylammonium hydroxide (TEAH). Remaining
carcasses were also solubilised in 35% TEAH. Radioactivity content in each sample was
measured by liquid scintillation counting. Total radioactivity in charcoal tubes was compared
to unchanged D5 determined by GC-MS analysis. The percent dose absorbed was
determined as the amount of radioactivity in carcasses, faeces, urine, skin dosing sites, and
cage rinses. Absorption of 14C-D5 after 168 hours was determined to be 0.089 ± 0.0302%.
Ref.: 23; AR1
Normal, healthy human volunteers (3 male, 3 female) were exposed to either 1.4 g (males)
or 1.0 g (female) of 13C-D5 by applying the D5 to the axilla. The dose was split between axilla
and applied once while the subject was breathing from a clean air source. Blood samples
were obtained prior to exposure and at 0.5, 1, 2, 4, and 6 hours. Exhaled air samples were
obtained prior to exposure and at 15, 30, 45, 60, 75, 90, 105, 120, 240, and 360 minutes
and at 24 hours after application. D5 levels were significantly elevated above baseline in
blood, plasma, and in exhaled air at all time points after application. The plasma and blood
levels of D5 after dermal application were less than 2.0 ng/g blood or plasma. With dermal
application of 1.0 g (female) or 1.4 g (males) of D5, peak plasma D5 levels were 1.22 ng/g at
1 hour and 0.61 ng/g at 6 hr post exposure. There was a relatively poor correlation between
blood levels and exhaled air levels of D5 especially at one hour after application, i.e.,
considerably higher levels were found in exhaled air than would have been expected based
on blood levels. D5 levels did not differ significantly between male and female volunteers.
Ref.: 24

General comment on dermal absorption
There is some variation in results of in vitro and in vivo studies with D5. In vitro an average
of 0.04% of decamethylpentacyclosiloxane (D5, applied neat or in antiperspirant
formulation) was absorbed in human cadaver skin and the receptor fluid after 24 h of
exposure (Ref. 20). Higher values were found in an in vitro study with rat skin, where

SCCS/1241/10
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dermal absorption of 14C-D5 was maximum 1.5% (Ref. 20). Similar to in vitro studies with
human or rat skin, also the in vivo rat study demonstrated that the majority (~ 85%) of D5
applied volatilized from the skin surface before being absorbed. Less than 1.0% of applied
D5 appeared to be absorbed in vivo in one rat study of lower quality (Ref. 22), whilst a
newer rat study showed 0.09% dermal absorption of D5 (ref. 23). Consistent with in vitro
results for human cadaver skin, pharmacokinetic modelling of dermal absorption in human
volunteers indicated for men and women that 0.05% of applied D5 was absorbed into
systemic circulation (Ref. AR2).
A value of 0.17% for dermal absorption of D5 was taken by the Canadian authorities (Ref.
AR13), based on the publication by Jovanovic et al. (2008; Ref. AR1).
3.4.5.

Repeated dose toxicity

3.4.5.1.

Repeated Dose (14 days and 28 days) oral / dermal / inhalation toxicity

Oral
Five groups of eight male and female Sprague-Dawley rats were administered by oral gavage
0, 25, 100, 400, or 1600 mg D5/kg bw, 5-days/ week for two weeks. All animals were
observed for signs of local and systemic toxicity, general appearance, behavioural
abnormalities, and mortality throughout the study. No treatment related deaths were
observed. No effects were seen on body weight or body weight gain, on behaviour or on gross
pathology. A treatment related increase in absolute and relative liver weight was seen in
females at 100 mg D5/ kg bw and in males at 25 mg D5/kg bw.
Ref.: 4
A similar study on short-term oral toxicity of D5 by Crofoot et al. (1990) was cited in a
recent report of the US Cosmetic Ingredient Review Expert Panel, 2009 (Ref. AR14). Five
groups of 8 male and 8 female Sprague-Dawley rats received oral doses (via gavage) of 0,
25, 100, 400, and 1600 mg/kg bw, five days/week for two weeks. Neither treatment-related
deaths, overt signs of toxicity, nor changes in behaviour were observed in any of the
groups. Treatment-related increases in liver weights were observed at doses as low as 100
mg/kg in female rats (LOEL). A no-observed-effect-level (NOEL) for liver weight of 100
mg/kg was reported for male rats. No significant changes were observed at gross
pathological examination.
Ref.: AR3
Comment
Similar observations were made in a 13-week oral gavage study (see section 3.4.5.2) that
derived a LOEL of 100 mg/kg bw/day.
A four week study was conducted in which 6 male and 6 female rats were given 1500 mg/kg
bw/day of the test substance via oral gavage 5 days a week for the duration of the study.
Animals were observed for signs of local or systemic toxicity, general appearance, behavioural
abnormalities and mortality. Body weight and food consumption were determined weekly. A
control group received distilled water. No treatment-related deaths, overt signs of toxicity or
changes in the behaviour were noted in any of the groups. Statistical comparison of mean body
weight and food consumption data indicated no treatment-related effects between the control
and the test groups. A statistically significant increase in absolute liver weight was observed
in female rats treated with 1500 mg D5/kg bw. No gross pathological changes were observed
in any of the organs or tissues of male and female rats in the control and test groups.
Ref.: 5

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

Inhalation
Five groups of ten male and female Fischer 344 rats were exposed by nose-only inhalation
for 6 hrs/day, five days/week for four weeks to 0, 0.44, 0.65, 1.50, or 2.29/3.71 mg D5/l (0,
28, 42, 96, 151/197 ppm, respectively). Animals were exposed to the highest exposure
concentration of 3.71 mg/l (197 ppm) for days 1 to 6 while the exposure to 2.29 mg/l (151
ppm) was for the remaining duration of the study (week 2 to 4). (According to AR#4, 160
ppm is the highest D5 exposure concentration that can be reliably generated and
maintained as a vapour without interference by aerosol formation). No behavioural
abnormalities or mortalities were seen during the study. No effects were seen on mortality,
body weight or body weight gain, food intake, or clinical signs. Urinalysis and biochemistry
data indicated no changes of toxicological significance at termination of the treatment.
However, a few minor changes with statistical significance were recorded in rats exposed to
1.5 and 2.29 mg/L (42 and 96 ppm). These were characterised by a slightly increased mean
corpuscular volume, slightly decreased mean corpuscular haemoglobin concentration and
slightly increased leukocyte and lymphocyte counts in males. There was no apparent
relationship between these effects and the treatment. An increase in absolute and relative liver
weight with slight hepatocellular hypertrophy (females only), increased incidence of goblet cell
proliferation in the nasal cavity (males and females), and minimal to slight interstitial
inflammation in the lungs (males and females) were observed at the highest exposure
concentration of 2.29/3.71 mg D5/L. i.e. 151 and 197 ppm.
Ref.: 6
Comment
The changes observed at the highest exposure concentrations (increased incidence of goblet
cell proliferation in the rat nasal cavity, and minimal to slight interstitial inflammation in the
lungs) are consistent with changes due to inhalation of a mild irritant. The local effects are
considered to be of little/no relevance for consumer exposure to much lower concentrations of
D5.
In female rats a LOEL of 160 ppm was set for systemic effects on liver (an increase in absolute
and relative weight with slight hepatocellular hypertrophy).
In a 28-day study in rats, D5 was administered via whole body inhalation to four groups of
male and female Fischer 344 rats for a period of six hours/day, seven days/week for four
consecutive weeks. The target exposure concentrations were 10, 25, 75 and 160 ppm. A
concurrent negative control group of identical design received only filtered air. After completion
of 28 days of exposure, 10 rats/sex/group were necropsied and 5 rats/sex/group entered a
two-week recovery period. Animals were observed for clinical signs, effects on body weight,
food consumption and ophthalmologic effects. Complete necropsies were performed, selected
organs weighed and selected tissues were examined grossly and microscopically. No test articlerelated effects on survival, clinical condition, body weights, body weight gains, food
consumption or ophthalmoscopy at any exposure level were observed in this study. No test
article-related gross findings were observed. An increased mean lung weight and alveolar
macrophage accumulation was observed in the 160-ppm group. Treatment-related
morphological alterations (Goblet cell proliferation) were also noted in the nasal cavity of both
sexes at concentration of 10 ppm of D5 or greater. These changes were reversible following a
two-week recovery period. The mean (absolute and relative) liver weights in the 160 ppm
group, especially the females, were increased at the week 4 primary necropsy. No
histopathological changes were noted. At the week 6-recovery necropsy, no effects on liver
weights were observed.
Ref.: 7
Comment
The treatment-related changes observed in lung and nasal cavity of rats at 160 ppm are local
effects of little/no relevance for consumer exposure to low concentrations of D5. A LOEL of 160

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ppm was found for systemic effects on liver (an increase in absolute and relative weights, with
no histopathological changes). The effect was reversible upon cessation of exposure.
Ten male and 10 female Wistar rats were exposed via whole body inhalation to 0.081, 0.432
or 2.00 mg D5/l (5, 28, or 129 ppm, respectively), 6 hrs/day, 5 days/week for four weeks.
Five animals of each sex were allowed a 14-day recovery period following the four weeks of
exposure. A concurrent control of identical design was exposed to only filtered air. Animals
were observed for clinical signs, effects on body weight, food consumption, and organ weights.
Haematology, clinical biochemistry, urinalysis and gross and microscopic pathology were
performed. In this study, no effects were seen on body weight, body weight gain, food
consumption, or clinical condition. There were no gross findings. At 0.432 mg D5/l (28 ppm)
and above, there was an increase in white blood cell and neutrophil counts (males only) a
decreased number of red blood cells and mean corpuscular haemoglobin concentration. An
increase in relative liver weight (percentage not stated) was also observed in male and
female rats at 0.432 mg D5/l (28 ppm) and above. All effects were reversible during the 14day recovery period. The NOAEL reported in this study was 0.081 mg D5/L air (5 ppm).
Ref.: 8
Comment
A LOEL of 28 ppm D5 was reported based on changes of some haematological parameters and
reversible effects on liver (an increase in relative weight, percentage not stated) in this study of
1984. However, neither two more recent rat studies with 4-week inhalation nor studies with
longer exposure did observe such changes at similar concentrations. Thus, SCCS as well as the
Canadian authorities (Ref. AR13) have not further considered this study of 1984 in their
assessment of D5.
Dermal
A subacute dermal toxicity study of D5 was conducted in rats. In this study, 10 male and 10
female Sprague-Dawley rats were treated with D5 dermally under occlusive conditions at
dose levels of 0, 200, 800, and 1600 mg/kg bw/day. Treatments were for 6 hours per day, 7
days per week, for 28 days. A control and a test group, each consisting of five male and five
female rats, were treated respectively with 0 and 1600 mg/kg bw and observed for 14 days
after the treatment period for reversibility, persistence and delayed effects. Animals were
observed for signs of local or systemic toxicity, general appearance, behavioural
abnormalities and mortality. Food consumption and body weights were determined weekly.
After 28 days, blood and urine samples were collected and the animals were sacrificed and
examined for histopathological changes. No mortality, overt signs of toxicity or behavioural
changes were noted in any of the groups. A comparison of mean body weight, food
consumption or haematological data between control and test groups showed no treatmentrelated effects. The few statistically significant differences in clinical chemistry parameters
between the control and test groups were within normal biological variation. No treatmentrelated effects were identified by histopathology at either the terminal or recovery
sacrifices. Based on urinalysis, there was some evidence of dermal absorption and
metabolism. Under the test conditions, dermal applications of D5 at a dose level of up to
1600 mg/kg bw did not produce significant toxicological effects.
Ref.: 9
Six male and female New Zealand white rabbits were treated 6 hrs/day, 7 days/wk for 21
consecutive days with 1000 mg D5/kg bw under occlusive conditions. The skin was abraded
in one-half of the animals. Skin reactions were scored daily for signs of oedema and
erythema. At necropsy, the heart, lungs, liver, kidneys, spleen, testes, epididymides, ovaries,
and urinary bladder were weighed and preserved. No clinical signs of toxicity were observed.
There was no effect on body weight, no mortality, no effect on organ weights, and no
treatment related gross pathology findings. No signs of skin irritation were observed.
Ref.: 16
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An unspecified number of male and female New Zealand white rabbits were exposed dermally
to 0, 96, 288, or 960 mg D5/kg bw for 5 day/wk, for three weeks. The treatment period was
followed by a two-week recovery period. Animals were observed for clinical signs of toxicity,
mortality, and body weight changes. Haematology, clinical biochemistry, gross examination, and
histopathology were performed. No effects were seen on clinical condition, survival, or body
weight. No substance related findings were seen on gross examination or histopathology.
Ref.: 17
Conclusion
LOEL/NOEL for D5
Studies on repeated dose toxicity with two week oral application of D5 (Ref. 4) revealed a
LOEL of about 100 mg/kg bw. The treatment related increases in absolute and relative liver
weight in rats at 100 mg D5/kg bw can be considered as an adaptive response.
In studies on repeated dose toxicity with inhalation exposure a LOEL of 160 ppm was found
for systemic effects of D5 on rat liver (increase in absolute and relative weights). The effect
was reversible upon cessation of exposure.
A NOAEL of 1600 mg/kg bw was found in studies conducted in rats with dermal application of
D5 up to 4 weeks.
3.4.5.2.

Sub-chronic (90 days) oral / dermal / inhalation toxicity

Oral
Male and female Wistar rats were administered 100, 330, or 1000 mg neat D5/kg bw daily
for 13 weeks by gavage. Animals were observed for clinical signs, effects on body weight, food
consumption and ophthalmologic effects. Complete necropsies were performed, selected organs
weighed and selected tissues grossly and microscopically examined. No effects were seen on
body weight or body weight gain or on food consumption. No effects were seen on blood or
haematopoetic organs. Increases in liver weight in both males and females were seen at all
dose levels. No significant effects related to D5 exposure were seen on histopathology.
Ref.: 10
Inhalation
Male and female Fischer 344 rats of both sexes were exposed by nose only inhalation to D5
6 hours/day, 5 days/week for 13 weeks. Each exposure concentration group had 20 male
and female rats except for the control and highest exposure concentration groups, which
contained 30 males and females each. Ten of the control and high exposure concentration
male and female rats were used for a treatment-free recovery period of 4 weeks. The
achieved test atmosphere concentrations, based upon analytical determination of the
vapour phase, were 0, 28.6, 49.2, 87.7 or 233 ppm (0.44, 0.758, 1.35, or 3.59 mg D5/l,
respectively). No mortality was observed in any of the treated or control groups and no clinical
signs of toxicity were noted which were considered treatment-related.
Following the recovery phase, initial differences in body weight gains between 233 ppm and
the control group diminished. Analysis of organ weight data indicated statistically significant
increases in liver weight (relative and absolute) for the 49.2 and 87.7 ppm (female) and 233
ppm (female/male) groups after treatment. The most apparent clinical biochemistry findings
included a dose-related increase in gamma-glutamyltransferase activity in female rats. Lung
weights remained elevated in the 233-ppm group (female) after the recovery phase.
Reductions in thymus, testis and ovary organ weights were observed after the recovery phase
in the high exposure (233 ppm) group only. Possible treatment-related histopathological
findings included an increased incidence of ovarian interstitial gland hyperplasia and vaginal
mucosal mucification and atrophy in the female rats exposed to 233 ppm.
Slight, not statistically significant, ovaries and testes weight decrease was also observed.
Ref.: 11

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

Comment
The achieved levels of D5 were slightly higher than the target exposure levels (0, 26, 46 and
224 ppm) which have been quoted in previous assessments of D5 (Refs. AR12, AR13).
Two groups of ten male and ten female Sprague-Dawley rats each were exposed to D5
vapours at 1 and 120 ppm for six hours/day, seven days/week for 28 days. Four other
groups were exposed to 0, 20, 59 and 119 ppm D5 in a similar regime for a period of 13
weeks. A control and test group consisting of 10 male and female rats each were exposed,
respectively, to 0 and 120 ppm for 13 weeks and were observed for 28 days for reversibility,
persistence or delayed toxic effects. The 120-ppm female 90-day terminal sacrifice group had
a statistically significant increase in relative liver weight when compared to controls. The
liver weight in females returned to normal values at the end of the recovery period. Under
the same test conditions, D5 caused no biological or toxicological effect in male rats.
Ref.: 12
Conclusion
A subchronic (13 week) toxicity study with oral application of D5 revealed a LOEL of 100
mg/kg bw, based on liver weight increases in both male and female rats (Ref. 10).
In studies with 3 months inhalation exposure of D5 a LOEC of 49/46 ppm was found, based
on effects on rat liver, i.e. an increase in liver weight and gamma-glutamyltransferase activity,
and a decrease in LDH activity in female rats (Ref. 11).
3.4.5.3.

Chronic (> 12 months) toxicity

See section 3.4.7. Carcinogenicity
3.4.6.

Mutagenicity / Genotoxicity

3.4.6.1

Mutagenicity / Genotoxicity in vitro

D5 was evaluated for genetic activity in a battery of microbial assays and in vitro
mammalian cell culture assays employing Salmonella typhimurium (TA-1535, TA-1537, TA1538, TA-98, and TA-100) and Escherichia coli (W3110/polA+, P3478/polA-) indicator
organisms and L5178Y mouse lymphoma cells, respectively. The test substance showed no
mutagenic activity in the Ames bacterial test with and without S9 microsomal activation and
was inactive in the mammalian cell culture system at concentrations up to 25 µl/ml.
Ref.: 31, 32
Bacterial Reverse Mutation Assay
The potential for D5 to induce gene mutations was further investigated using the Salmonella
typhimurium strains TA 1535, TA 1537, TA 98, and TA 100 and the Escherichia coli strain
WP2 uvrA. The assay was performed in two independent experiments both with and without
liver microsomal (S9-mix) activation. Each concentration, including controls, was tested in
triplicate. D5 was tested at the following concentrations: 33, 100, 333, 1000, 2500, and
5000 µg/plate. The plates incubated wit D5 showed normal background growth up to 5000
µg/plate with and without metabolic activation in all strains used. No toxic effects, evident
as a reduction in the number of revertants, occurred in the test groups with or without
metabolic activation. No substantial increase in revertant colony numbers in any of the five
tester strains was observed following treatment with D5 at any dose level with or without
metabolic activation. Under the experimental conditions of these studies, D5 did not induce
gene mutations by base pair changes or frameshift mutations in the genome of the strains
tested. Therefore, it is concluded that D5 is non-mutagenic.
Ref.: 33
74

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Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

In vitro Chromosomal Aberration Test
In another in vitro experiment, D5 was dissolved in ethanol and was assessed for its
potential to induce structural chromosome aberrations using Chinese hamster V79 cells in the
absence and presence of S9 metabolic activation. In each experimental group, two parallel
cultures were set up. One hundred metaphase plates were scored for structural chromosome
aberrations per culture. In the absence of the S9-mix in both experiments, toxic effects
indicated by reduced cell numbers and/or mitotic indices of below 50% of control were
observed. When the S9 fraction was present, there were no toxic effects seen on the cells. In
both independent experiments, neither a statistically significant nor a biologically relevant
increase in the number of cells carrying structural chromosomal aberration was observed
after treatment with the test material. No increase in the frequencies of polyploid
metaphases was found after treatment with the test material as compared to the
frequencies of the controls. In conclusion, under the experimental conditions reported, the
test material did not induce an increase in cells with structural chromosome aberrations as
determined by the chromosome aberration test in Chinese hamster V79 cells in vitro.
Therefore, D5 is considered to be non-clastogenic in this chromosome aberration test with
and without metabolic activation when tested up to cytotoxic concentrations and up to the
highest recommended concentrations.
Ref.: 34
3.4.6.2

Mutagenicity/Genotoxicity in vivo

In vivo UDS and Micronucleus Test
The mutagenic potential of D5 was assessed using in vivo Unscheduled DNA Synthesis (UDS)
and micronucleus assays. The D5 was administered to Fischer male and female rats by
whole body vapour inhalation. The animals were treated daily for 6 hours with 160 ppm of D5
for 7 consecutive days. Filtered air was used for the negative control group. The animals of the
positive control groups were treated in the same way as the air control groups. However,
following the last exposure they were treated orally (by gavage) with the corresponding
positive control. 2-Acetylamino-fluorene (2-AAF) and cyclophosphamide were used as the
positive controls for the UDS and micronucleus assays, respectively.
For analysis of DNA repair (UDS) in treated rat hepatocytes, the animals were killed five hours
and 16 hours after the last treatment. Primary hepatocytes were obtained by liver perfusion and
hepatocyte cultures were established and exposed for four hours to methyl-³H-thymidime
(3HTdR), which was incorporated if UDS occurred. For each experimental group including the
controls, hepatocytes from 6 treated animals per sex were assessed for the occurrence of
UDS. The viability of the hepatocytes was not affected by the in vivo treatment with D5 and
D5 did not cause UDS induction at any dose level in the hepatocytes as compared to concurrent
air controls. Treatment with 2-AAF (100 mg/kg) revealed distinct increases in the number of
nuclear and net grain counts.
Twenty-four hours after the last treatment, bone marrow cells of the respective animals were
collected for micronucleus analysis. For each experimental group including controls, bone
marrow cells from six treated animals per sex were assessed for the occurrence of
micronuclei. The test material did not exert any cytotoxic effect. There was no biologically
relevant or statistically significant enhancement in the frequency of detected micronuclei
compared to air controls following treatment with D5. Cyclophosphamide (40 mg/kg)
showed a substantial increase of induced micronucleus frequency, indicating the test system
was sensitive and valid.
Exposure to D5 neither induced DNA damage leading to increased repair synthesis in the
hepatocytes of treated rats nor induced micronuclei. Therefore, D5 is considered to be nongenotoxic in these assays.
Ref.: 35
75

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Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

Conclusion on mutagenicity
The negative results obtained in the bacterial reverse mutation assay, in vitro chromosomal
aberrations in Chinese Hamster V79 cells, unscheduled DNA synthesis, and in vivo
micronucleus assays indicate that D5 does not possess mutagenic or genotoxic potential.
3.4.7.

Carcinogenicity / Chronic Toxicity

In a 24-month combined chronic/oncogenicity inhalation study, male and female Fischer 344
rats were exposed to vapour concentrations of 0, 10, 40, or 160 ppm D5 for 6 hr/day, 5
days/week, for up to 24 months. The study animals were divided into four groups (Table 8).
Group A animals consisting of six animals per sex were exposed for six months and then
sacrificed for the determination of the D5 concentration in liver, fat, and plasma. Group B,
consisting of 10 animals per sex, were exposed to D5 for 12 months and then sacrificed. Group
C animals, consisting of 20 animals per sex, were exposed to D5 for 12 months only and then
observed for an additional 12 months to determine the possible reversibility of any effects.
Group D animals, consisting of 60 animals per sex, were exposed to D5 for 24 months. Both
group C and D animals were sacrificed at 24 months. All animals were monitored for
mortality, clinical signs, food consumption and body weights. Clinical laboratory
investigations included haematology, clinical biochemistry, and urinalysis at 3, 6, and 12
months. The lungs, liver, kidney, nasal cavity, gross lesions and tissue masses from all group
B, C, and D animals were submitted for histological examination. A complete histopathology
examination was performed on all tissues from the control and high dose group animals from
groups B, C, and D as well as suspected target organ tissue from intermediate exposure
level groups.
Ref.: 36
Table 8:

D5 Combined Chronic/Oncogenicity Study Design
Subgroups

Exposure
Concentration

0 ppm
10 ppm
30 ppm
160 ppm

A
6-month tissue
level
determination
6M/6F
6M/6F
6M/6F
6M/6F

B
12-month
chronic toxicity
group
10M/10F
10M/10F
10M/10F
10M/10F

C
chronic toxicity
recovery group

D
oncogenicity
group

20M/20F
20M/20F
20M/20F
20M/20F

60M/60F
60M/60F
60M/60F
60M/60F

Group A Results
Group A animals were used for the analysis of D5 levels in blood, fat, and liver in order to
validate the PBPK model developed for D5. An increased incidence of hyaline inclusions in
the nasal respiratory/olfactory epithelium was noted in male and female rats at 160 ppm.
This finding was considered a non-specific treatment-related effect (changes consistent with
chronic inhalation of a mild irritant).
Group B Results
No effects were seen at one year of exposure that could be related to D5.
Group C Results
Endometrial adenomatous polyps and adenocarcinomas were observed in animals exposed
to D5 for one year followed by one year of recovery (Table 9). The incidence of endometrial
76

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___________________________________________________________________________________________

adenocarcinoma was 1, 1, 0 and 2 for female rats in the 0, 10, 40 and 160-ppm exposure
groups. Endometrial adenomatous polyp was diagnosed in one female rat in the 160-ppm
exposure group. Combining adenomatous polyps with the adenocarcinoma data, the
combined incidence becomes 1, 1, 0 and 3 for female rats in the 0, 10, 40 and 160-ppm
exposure groups, respectively. Uterine endometrial adenoma was not present in Group C
female rats.
Peto's test showed there was no significant trend among the groups (p=0.4159) when all
tumours were combined. Likewise, when the adenocarcinomas were analysed separately,
there was no significant trend (p=0.8227). Fisher's Exact test showed there was no
significant difference in the proportion of tumour occurrences among the groups (p=0.3867)
when all tumours were combined or when the tumours were analysed separately (p=O.8988).
The poÌy-3 test showed there was no significant trend among the groups when all tumours
were combined (p=0.0580). When the adenocarcinoma tumours were analysed separately
using the poly-3, there was no significant trend (p=0.1754).
Group D Results
An increased incidence of hyaline inclusions in the nasal respiratory/olfactory epithelium was
noted in male and female rats at 160 ppm. This finding was considered a non-specific,
treatment-related effect.
The incidence of endometrial adenocarcinoma in Group D was 0, 1, 0 and 5 for female rats in
the 0, 10, 40 and 160-ppm exposure groups, respectively (Table 10). One female rat in the
0 and one female in the 40-ppm exposure groups, respectively, were diagnosed with
endometrial adenomatous polyps. The combined tumour incidence for female rats in Group D
was, therefore, 1, 2, 1 and 5 in the 0, 10, 40 and 160-ppm exposure groups, respectively.
For animals exposed for 2 years (Group D), Peto's test showed there was no significant trend
among the groups when all tumours were combined (p=0.1314). When the adenocarcinomas
were analysed separately, a significant trend was found (p < 0.05). Fisher's Exact test showed
there was no significant difference in the proportion of tumour occurrences among the groups
when all tumours were combined (p=0.3233). There was a significant difference when the
adenocarcinoma tumours were analysed separately (p< 0.05). Analysis of the tumour
incidence in females exposed for two years using the poly-3 test showed a significant trend
among the groups when all tumours were combined (p<0.05) and when the
adenocarcinomas were analysed separately (p<0.001).
Table 9:
Group C Uterine Tumour Incidence after 12 months exposure to D5 plus 12
months recovery in air
Exposure
Concentration
0 ppm
10 ppm
40 ppm
160 ppm

Endometrial
Adenocarcinomas
1/20
1/20
0/20
2/20

Adenomatous
Polyps *
0/20
0/20
0/20
1/20

Total
1/20
1/20
0/20
3/20

significant positive trend test (p<0.05) by the Poly3 test

Table 10: Group D Uterine Tumour Incidence after 24 months exposure to D5
Exposure
Concentration
0 ppm
10 ppm
40 ppm
160 ppm

a
*

Endometrial
Adenocarcinomas
0/60
1/60
0/60
5/60

a,*

Adenomatous
Polyps
1/60
0/60
1/60
0/60

Endometrial
Adenomas
0/60
1/60
0/60
0/60

significant positive trend test (p<0.05) by the Peto test
significantly higher (p<0.05)than control by the Fisher's Exact Test

Total
1/60
2/60
1/60
5/60

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

The study authors note that there was a complete lack of an increase in incidence or severity of
uterine endometrial hyperplasia in Group B, C and D females. Endometrial hyperplasia is
considered
an
essential
precursor
lesion
commonly
associated
with
uterine
adenoma/carcinoma. Some hyperplasia was found in a later analysis of the pathology slides
[Ref. AR5].
For uterine endometrial adenocarcinomas alone, the data show a statistically significant
increase at a D5 exposure concentration of 160 ppm for two years. Work has been
performed to address the potential mode of action for the formation of these tumours in this
study. The results of this work are described in section 3.3.12 (special investigations).
Ref.: 36
Comment
Carcinogenicity of D5 was significant only at the highest concentration of 160 ppm. There is
uncertainty whether the uterine tumours are relevant or are not relevant to humans. It is
recognized that D5 may possibly act as a dopamine agonist, thus contributing to the
observed tumourigenic effects in female rats. The applicant states that this mode of action
is not relevant to humans (Ref.: 66). However, this position has not been adopted so far by
the California OEHHA (2007) due to insufficient data for a thorough mode-of action analysis.
The SCCS considered that there is insufficient data for this suggested neuroendocrine mode
of action in rats to preclude a relevance for humans. The absence of a genotoxic potential
supports the view that tumour formation is due to threshold effects.
3.4.8.

Reproductive toxicity

3.4.8.1.

One generation reproduction toxicity

A screening study was designed to determine the exposure levels appropriate for studying the
potential adverse effects of D5 vapours on male and female reproduction in rats. The test
article was administered via whole body inhalation to three groups each of 22 male and 22
female Sprague Dawley rats. Exposure levels were 26 or 132 ppm. A control group was
exposed to clean, filtered air. The exposure period was 6 hours per day, 7 days/wk for a
minimum of 28 days prior to mating and lasted until the day of necropsy for each animal, with
the following exception: exposure of the females was suspended from gestation day 21 through
lactation day 4. All animals were observed twice daily for appearance and behaviour. Body
weights were recorded weekly for both sexes prior to mating; maternal body weights were also
recorded on gestation days 0, 7, 10, 14 and 20 as well as on lactation days 1, 4, 7, 14 and
21. Food consumption was measured for corresponding intervals prior to mating, during
gestation and during lactation. All of the females were allowed to deliver and rear their pups
to weaning on postnatal day 21 (PND 21). The offspring were euthanized on PND 28. The
surviving dams were necropsied on lactation day 21. The males were necropsied after the
breeding period. In these animals, reproductive parameters (fertility, mating, days between
pairing and coitus, gestation and parturition), mean body weights, body weight gains and
food consumption, mean numbers of implantation sites and mean live litter size were not
adversely affected by test material exposure at exposure levels of 26 or 132 ppm. No
exposure-related effects on pup viability throughout lactation and no exposure-related clinical
signs were noted in the pups in either the 26 or 132-ppm groups. Pup sex ratios and mean
pup weights were unaffected by exposure to the test material at any exposure level. No
internal findings related to the test material were noted at either exposure level in females
necropsied on post-mating day 25 (10). The NOAEL for this study was > 132 ppm.
Ref.: 25

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

3.4.8.2.

Two generation inhalation reproduction and developmental neurotoxicity study

A 2-generation reproductive study was conducted with D5 to evaluate the potential adverse
reproductive effects of whole-body vapour inhalation exposure of F0 and F1 animals to D5.
Neonatal survival, growth, and development of the F1 and F2 generations were evaluated.
The potential for D5 to cause functional and morphological changes to the nervous system
of the developing F2 rats following exposure of the F0 and F1 generations was also
evaluated. Groups of male and female Crl:CD®(SD)BR rats (30/sex/group) were exposed to
D5 for six hours daily for at least 70 consecutive days prior to mating. Target test article
concentrations were 30, 70 or 160 ppm. A control group of identical design was exposed to
clean, filtered air on a comparable regimen. Exposure of the F0 and F1 males continued
throughout mating and through the day prior to euthanasia. The F0 and F1 females were
exposed throughout mating and through gestation day 20 at which time exposures were
stopped. Exposures were re-initiated on lactation day 5 and continued through the day prior
to euthanasia. All animals were observed twice daily for appearance and behaviour. All F0
and F1 females were allowed to deliver and rear their pups until weaning on lactation day
21. Offspring (30/sex/group) from the pairing of the F0 animals were selected to constitute
the F1 generation. Developmental landmarks (balanopreputial separation and vaginal
patency) were evaluated for the selected F1 rats. Thirty pups/sex/group from the F2
generation were selected for development landmarks, neurobehavioral testing,
neuropathology brain weights and/or brain dimension measurements. Surplus F1 and F2
pups were necropsied on PND 21 or 28, and selected organs were weighed. Selected F2 rats
not allocated for neuropathology and brain dimension measurements were necropsied on PND
70; selected organs were weighed. All surviving F0 and F1 parental animals received a
complete detailed gross necropsy following the completion of weaning of the F1 and F2 pups,
respectively; selected organs were weighed. Spermatogenic evaluations were performed on
all F0 and F1 males and ovarian primordial follicle and corpora lutea counts were recorded
for F0 and F1 females in the control and high-exposure groups. Designated tissues from all
F0 and F1 parental animals in the control and 160 ppm groups, from all parental animals that
were found dead or euthanized in extremis, and from F2 pups selected for neuropathological
evaluation were examined microscopically.
No clear exposure-response relationship for the mortalities was evident for the six F0 animals
that died or were euthanized in extremis and no consistent target organ could be identified at
the gross and microscopic examinations of these animals. The mortalities and moribundity
of these F0 males and females were not attributed to test article exposure. All other F0 and
all F1 parental animals survived to the scheduled necropsy. No exposure-related clinical
signs were noted at any test article concentration.
Reproductive parameters (days between pairing and coitus, mating indices, fertility indices,
duration of gestation, and parturition) in the F0 and F1 generations were not adversely
affected by exposure to the test article. Mean weekly, gestation, and lactation body weights,
body weight gains, and food consumption were not adversely affected by test article exposure
at any concentration in the F0 and F1 generations. Functional observational battery (FOB) data
(home cage, handling, and open field observations) for the F1 females revealed no exposurerelated effects at the gestation day 10 and lactation day 20 evaluations.
No exposure-related gross internal findings were noted at any concentration in the F0 and F1
animals at the scheduled necropsy. No exposure-related differences in mean organ weight data
(absolute and relative to final body weights and brain weights) were noted at any concentration
in the F0 and F1 generations. F0 and F1 mean ovarian primordial follicle counts were unaffected
by exposure in the 160 ppm group. Spermatogenic endpoints (testicular and epididymal sperm
numbers, sperm production rate, sperm motility, and sperm morphology) were not affected by
test article exposure at concentrations of 30, 70 or 160 ppm.

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

F1 and F2 mean live litter sizes, numbers of pups born, percentages of males per litter at birth,
postnatal survival, and anogenital distances were not affected by parental exposure at any
concentration. One F0 female in the 160-ppm group had total litter loss on lactation day 0.
Because no exposure-related decreases in postnatal survival of the F1 and F2 litters were noted
at any concentration, the single occurrence of total litter loss in the 160-ppm group was not
attributed to D5 exposure. Mean pup body weights and the general physical condition of the
F1 and F2 pups were similar in control, 30, 70 and 160 ppm groups both before and after
weaning. Necropsy findings for the F1 and F2 pups that were found dead or euthanized in
extremis were not suggestive of any correlation with parental exposure. At the scheduled
necropsies of F1 and F2 surplus pups on PND 21 or 28, no gross internal findings or differences
in mean organ weight data, which could be attributed to parental exposure, were noted at any
concentration. F1 and F2 developmental landmarks (balanopreputial separation and vaginal
patency) and F2 neurobehavioural responses (motor activity, startle response, Biel maze and
FOB data) were not affected by parental exposure. At the PND 11 and PND70 neuropathological
evaluations, no microscopic findings or differences in mean brain weights and brain
measurements related to parental exposure were noted for any of the selected F2 rats. No gross
internal findings or differences in mean brain weights, which could be attributed to parental
exposure, were noted at the PND 70 necropsy of F2 rats not selected for neuropathological
evaluation.
In conclusion, no parental toxicity in the F0 and F1 generations was seen at exposure
concentrations of 30, 70 or 160 ppm. F0 and F1 reproductive performance was not affected
at any concentration. No test-article-related total litter losses occurred. No neonatal toxicity
was evident in the F1 and F2 generations at concentrations of 30, 70 or 160 ppm. No F2
developmental neurotoxicity was evident at any concentration. Based on the results of this
study, the NOAEL (no-observed-adverse-effect level) for parental toxicity, reproductive
toxicity, neonatal toxicity, and developmental neurotoxicity is considered to be 160 ppm.
Ref.: 26
Comment
Results of the 2-generation reproductive toxicity study were published recently in a peer
reviewed journal (Ref.: AR4).
In line with the above description, the authors found no treatment-related gross findings or
organ weight effects at the F0 and F1 necropsies, except for a 10% increase in liver weight
at 160 ppm in F0 females, and minimal alveolar histiocytosis in all exposed groups. No
significant changes between D5-treated and control groups were noted in reproductive
parameters in the F0 and F1 parental animals. Mean live litter sizes, number of pups born,
sex ratios, pup body weights, postnatal pup survival, and the general physical condition of
offspring in each generation were not affected. There was a slight, but statistically
significant, increase in the mean F1 male pup anogenital distance (AGD; was not measured
in F1 male pups exposed to 30 and 70 ppm D5). An increase in male pup anogenital
distance may indicate an anti-estrogenic or androgenic effect. Yet, other studies (see
section 3.3.12) failed to show such hormonal activity for D5. Vaginal patency and
balanopreputial separation were unchanged compared to controls. The authors suggested a
NOAEL of 160 ppm D5 for parental and reproductive toxicity.
Conclusion
For developmental and reproductive toxicity a NOAEL of 160 ppm D5 can be derived from
the two-generation study.
3.4.8.3.

Teratogenicity

Prenatal developmental study
See above section 3.4.8.2

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

3.4.9.

Toxicokinetics

Absorption and Distribution
In an exploratory study to determine the time points and dosing for a definitive study, 48
female and 3 male F344 rats were exposed to 160 ppm 14C-D5 via nose only inhalation for a
single six-hour time period. An additional 3 female rats were used as controls to establish
background matrix effects on measurement of radioactivity. Body burden animals were
counted in toto. Pelts and carcasses were counted separately. Blood, plasma, and/or
selected tissues were collected at 1.5, 3, and 4.5 hours during exposure and at 8 time points
post-exposure. Expired air, urine and faeces were collected at specified intervals during a
168-hour period post-exposure. The mean achieved dose was 88 ± 2 µCi and the mean
body burden dose was 2 ± 0.6 µCi (approximately 3% of the achieved dose). A mean of 97 ±
26% of the body burden dose was recovered from the mass balance group. Plasma toxic
kinetic values were calculated: t½ = 58.9 hours; AUC = 77 µg x hr/gm; tmax = 0 hr postexposure and Cmax = 3.39 µg/ml.
Ref.: 27
The disposition of D5 in male and female Fischer 344 rats following single or multiple
inhalation exposures was evaluated. Animals were administered a single 6 hour nose-only
exposure to 7 or 160 ppm 14C-D5 or fourteen 6-hour nose-only exposures to unlabeled D5
followed on the 15th day by a 6-hour exposure to 14C-D5. Subgroups of exposed animals were
established to evaluate body burden, distribution, and elimination. Samples of plasma, fat,
liver, lung, faeces and expired air were also processed for parent D5 analysis. Retention of
D5 following single exposures was relatively low (~4-5% of inhaled D5), with ~8-10%
retained following multiple exposures. Approximately 50-80% of this retained dose was
attributed to deposition on the fur for males and ~60-70% for the females. Parent compound
and radioactivity were widely distributed to tissues of both males and females, with
maximum concentrations observed in the majority of the tissues by 3 hours post-exposure.
D5 was distributed to fat, with elimination of parent and radioactivity occurring slower
compared to plasma and other tissues.
Ref.: 28, AR6
Elimination
The elimination of D5 from male and female Fischer 344 rats following single and multiple
inhalation exposures was evaluated. Elimination of retained radioactivity in urine (~12%) and
faeces (~16%) was similar for both sexes following all exposures. The radioactivity in
exhaled air was similar for both sexes following multiple exposures and females following single
exposure (~45%) with significantly higher amounts for the males following a single exposure
(~72%). In the plasma, liver and lung, the majority of radioactivity immediately following
exposure could be attributed to parent, with this decreasing over time to a small fraction
attributable to parent from 24 to 168 hours post exposure. In the urine samples, several
peaks were present, but none corresponded to the retention time of parent D5. In contrast,
the major peak found in the faeces corresponded to the retention time for parent D5.
Ref.: 28, AR6
Metabolism
The metabolic profile of D5 in rats was obtained using a high-pressure liquid
chromatography (HPLC) system equipped with a radioisotope detector. The HPLC
chromatogram revealed two major metabolites and five minor metabolites in the urine of
female rats administered 14C-D5 orally. The two major metabolites were dimethylsilanediol
[Me2Si(OH)2] and methylsilanetriol [МеSi(ОН)3]. No parent D5 was found in the urine. The
minor metabolites were identified as: [MeSi(OH)2-O-Si(OH)3], [MeSi(OH)2-O-Si(OH)2Me],
[MeSi(OH)2-O-Si(OH)Me2], [Me2Si(OH)-O-Si(OH)Me2], and [Me2Si(OH)-O-SiMe2-OSi(OH)Me2].
81

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Opinion on cyclomethicone (D4 / D5)
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In addition, the presence of D4D'OH and D4D'СН2OH also were detected in the urine using
GC-MS. The formation of D4D'OH and MeSi(OH)3 clearly shows demethylation at the siliconmethyl bonds.
Ref.: 29, 30
Comment
Results on the metabolism of D5 in Fisher 344 rats have been published also in a peer
reviewed journal (AR7). The authors identified at least ten metabolites by GC-MS analysis
(see above), and report that D5 metabolism in rats is extensive, with no parent compound
detected in urine.
Bioaccumulation
A concern with lipophilic compounds is the possibility of bioaccumulation. Usually, this occurs
with compounds that are both lipophilic and very slowly cleared from the body. While D5 is
very lipophilic with fat:blood partition coefficients between 500 and 1000, it also has high
clearance by both metabolism and exhalation following all routes of exposure. The possibility
of bioaccumulation of this compound has been tested by evaluating blood and tissue
concentrations of D5 after long-term inhalation exposures. In toxicity studies, rats were
exposed 5 days per week for 6 months and killed immediately after the last day of exposure
(group A animals of the studies described in section 3.4.7). D5 levels in plasma and fat
increased with exposure levels (10-160 ppm). D5 reached 2.2 and 3.19 µg/ml in plasma of
male and female rats at the highest dose, and about ten-fold higher levels in the fat of male
rats. In the fat of females, the levels were three to six times higher than those in male rats.
Ref.: 36
The PBPK model developed based on the 1 and 15 day exposure studies (Ref. 28; AR#6)
successfully predicted tissue levels in the 6-month group. No appreciable increase in any
tissue was predicted between the 15-day exposures and the 6-month exposure period, and
none was observed. The 6-month fat concentrations were actually somewhat lower than the
15-day exposures because of the different exposure regimens, i.e., every day versus 5 days
per week. Because D5 is rapidly eliminated by pulmonary and metabolic clearance, tissue
concentrations, even in fat, do not increase with repeated exposures.
For more information on PBPK models developed to predict D5 kinetics for dermal,
inhalation and oral exposure see section 3.4.12. (special investigations).
3.4.10.

Photo-induced toxicity

Siloxanes (such as D5) contain only methyl groups, which have no double bonds and do not
absorb ultra violet (UV) light. Consequently, no phototoxicity studies have been performed.
3.4.11.

Human data

Studies with D5 which involved humans are described above in section 3.4.3. (HRIPT, Ref.
19) and 3.4.4. (in vivo percutaneous absorption, Ref. 24).
These data obtained from humans subjects at the University of Rochester were used in
Pharmacokinetic modelling and are described below in section 3.4.12 (Ref. 61).
3.4.12.

Special investigations

Immunotoxicology
In order to assess the potential immunomodulatory consequences of inhalation exposure to
D5, male and female Fischer 344 (F344) rats (25/group) were exposed by whole body vapour
inhalation to 0, 10, 25, 75, or 160 ppm of D5, 6 hours/day, for 28 days. Clinical signs, body
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weights, and food consumption were recorded. On the day following the final exposure, 10
rats/group/sex were euthanized and a complete necropsy performed. Following a 14-day
non-exposure recovery period, the remaining 5 rats/group/sex were necropsied. Body and
organ weights were obtained and a complete set of tissues taken for histopathology. Samples
were also collected for serum chemistry, haematology, and urinalysis. Immunotoxicologydesignated rats (10/sex/group) were immunized with sheep erythrocytes (sRBC) 4 days prior
to euthanasia and cyclophosphamide was administered i.p. to positive controls on days 24
through 28. The anti-sRBC antibody-forming cell (AFC) response was evaluated in a standard
plaque assay. Blood was also collected for examination in the anti-sRBC enzyme-linked
immunosorbant assay (ELISA). D5 inhalation exposure did not alter humoral immunity and
caused only minor, transient changes in haematological, serum chemistry, and organ weight
values. Histopathological changes were confined to the respiratory tract and appeared to be
reversible.
Ref.: 37
Hepatomegaly and Enzyme Induction
A number of studies conducted have shown that D5 causes a reversible hepatomegaly in male
and female rats following oral administration by gavage or inhalation exposure. Studies have
been conducted to examine this effect.
Female Fischer 344 rats were exposed by whole-body vapour inhalation to either 0 or 160 ppm
D5, six hours/day, five days/week for 28 days. Changes in the activity and relative abundance
of hepatic microsomal CYPs (CYP1A, CYP2B, CYP3A and CYP4A), EH, and UDPglucuronosyltransferase (UDPGT) were measured. Repeated inhalation exposure of rats to D5
increased liver size by 16% relative to controls by day 28. During a 14-day post-exposure
period, liver size in D5-exposed animals showed significant recovery. Exposure to D5 did not
change total hepatic CYP, but increased the activity of NADPH-cytochrome c reductase by 1.4
fold. An evaluation of CYPs in hepatic microsomes prepared from D5-exposed rats revealed a
slight (1.8-fold) increase in 7-ethoxyresorufin O-deethylase (EROD) activity, but no change
in immunoreactive CYP1A1/2 protein. A moderate increase (4.2-fold) in both 7pentoxyresorufin 0-depentylase (PROD) activity and immunoreactive CYP2B1/2 protein
(3.3-fold) was observed. Testosterone 6ß-hydroxylase activity was also increased (2.4-fold),
as was CYP3A1/2 immunoreactive protein. Although a small increase in 11- and 12hydroxylation of lauric acid was detected, no change in immunoreactive CYP4A levels was
measured. Liver mEH activity and immunoreactive protein was increased 1.7- and 1.4-fold,
respectively, in the D5-exposed group. UDPGT activity toward chloramphenicol was elevated
1.8-fold, while no change in UDPGT activity toward 4-nitrophenol was seen. These results
suggest that the profile for enzyme induction following inhalation exposure of female Fischer
344 rats to D5 vapours is qualitatively similar to that reported for phenobarbital, and
therefore, D5 may be considered as a weak "phenobarbital-like" inducer.
Ref.: 38
Groups of 3-4 rats per sex were administered D5 in corn oil by gavage at dose levels of 0
(control), 1, 5, 20 or 100 mg/kg for 4 consecutive days. Positive control animals received 50
mg/kg phenobarbital by intraperitoneal injection for 4 days. At the end of each experiment
the liver was removed, weighed, homogenized and microsomes prepared. The activities of 7pentoxyresorufin O-depentylase (PROD) and 7-ethoxyresorufin O-deethylase (EROD) were
determined. Immuno-chemical analysis was performed using different anti-CYP polyclonal
antibodies to determine CYP1A1/2, CYP2B1/2, CYP3A1/2, NADPH cytochrome P-450
reductase. Relative liver weight was increased in females at 20 and 100 mg/kg and in males at
100 mg/kg. CYP2B1/2 immunoreactive protein was significantly increased at 5 mg/kg and
above as was PROD activity in females (males at 20 and 100 mg/kg). EROD activity was
increased in males and females at 5 mg/kg and above (however, no changes were detected in
CYP1A1/2 immunoreactive protein in rats of either sex). CYP3A1/2 immunoreactive protein
was significantly increased in males at 100 mg/kg and females at 5 mg/kg and above.
NADPH cytochrome P450 reductase immunoreactive protein was significantly induced at ≥ 5
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mg/kg in males and ≥ 20 mg/kg in females, induction pattern was similar to that observed with
phenobarbital.
Ref.: 39
Human liver microsomes from a pool of seven individuals were incubated with marker substrates
in the presence or absence of D5 at concentrations ranging from 0.040 to 3.5 µΜ. In addition,
D5 was evaluated for its ability to function as a metabolism-dependent reversible or
irreversible inhibitor. For comparison, D5 was also evaluated for its ability to inhibit CYP1A1/2
and CYP2B1/2 in liver microsomes from rats treated with 3-methylcholanthrene and
phenobarbital, respectively. D5 does not appear to be a 2B1 inhibitor. D5 appears to be a
strong reversible metabolism-dependent inhibitor of rat CYP1A1/2. D5 appears to be a weak
competitive inhibitor of human CYP3A4/5 and a strong metabolism-dependent inhibitor of
human CYP3A4/5. D5 has little or no capacity to inhibit rat CYP1A1/2 and human CYP1A2,
CYP2A6, CYP2B6, CYP2C9, CYP2C19, CYP2D6, CYP2E1 and CYP4A9/11 activity in a reversible
metabolism-independent manner. D5 has little or no capacity to function as a metabolismdependent inhibitor of rat CYP2B1/2, human CYP1A2, CYP2A6, CYP2B6, CYP2C9, CYP2C19,
CYP2D6, CYP2E1 and CYP4A9/11 activity.
Ref.: 40
Estrogenicity
In order to assess whether the adenocarcinomas seen in the two-year combined chronic /
carcino-genicity study could be due to direct estrogenic effects, D5 was evaluated in a rat
uterotrophic assay using both ovariectomized Sprague-Dawley and Fischer 344 rats that were
exposed to the highest achievable vapour concentration of D5 (160 ppm) via whole body
inhalation for 16 hours/day for 3 days. Immediately following exposure animals were
euthanized and the effect of test article on uterine weight (wet and blotted) was evaluated.
Exposure to D5 did not result in an increase in any of the estrogenic endpoints measured in
either strain of rat. Subsequently, D5 was evaluated for its ability to bind to the oestrogen
receptor alpha. In a typical competition experiment, D5 (160 ppm) did not displace any of the
estradiol indicating that this material does not compete for the receptor-binding site. In an in
vitro luciferase reporter gene assay using MCF-7 cells transiently transfected with a plasmid
for estrogen receptor alpha and the luciferase gene, D5 did not activate the reporter gene at
10 µΜ, while 17β-estradiol resulted in the expected increase (35-fold increase at 10 nM
dose range). Using in vitro and in vivo assays, D5 did not elicit any estrogenic responses.
Ref.: 41, 42, published in Ref. AR8
Studies in mice dosed orally with either D5 or D4 (100 up to 1000 mg/kg bw) revealed
uterotrophic/estrogenic activity for D4; in contrast D5 was not estrogenic in this assay.
Ref.: AR9
Dopamine Agonism
To assess whether D5 could affect prolactin secretion through dopamine agonism, both in vitro
and in vivo studies were performed. Utilizing an in vitro cell line, derived from a rat pituitary
tumour (MMQ), 10 µΜ of D5 was shown to decrease maitotoxin-induced prolactin release by
55% without affecting viability of the cell line. In a short-term in vivo study, F344 rats were
pre-treated with reserpine, which causes a reduction in dopamine, which, in turn, causes
prolactin levels to increase. Animals were exposed via nose-only for six hours to 160-ppm of
D5 or air (controls). Blood samples were collected immediately at the end of the six-hour
exposure and analysed for prolactin. In this study, serum prolactin levels in the reserpine
treated controls were six fold greater than in the untreated controls. Exposure to 360-ppm of
D5 caused a 50% decrease in serum prolactin levels relative to the reserpine treated control
group, in phase 2 of this study, F344 rats were pre-treated with reserpine and then
administered 6 mg sulpiride/kg body weight prior to a six-hour exposure to 160-ppm of D5.
Sulpiride is a highly specific dopamine receptor antagonist. At the end of the six-hour
exposure, blood samples were collected immediately for prolactin measurements. In this
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study, sulpiride pre-treatment blocked the effect of D5 on prolactin levels. This indicates
that D5 acts on the pituitary as a dopamine receptor agonist in vivo.
Ref.: 43 (Abstract)
Comment
A related study (Ref. AR10, Dow Corning 2005b) was not submitted to SCCP/SCCS. The
OEHHA (2007) pointed out that some desirable controls were missing and that no attempt
to determine a dose-response relationship was reported (Ref.: AR12).
Physiologically Based Pharmacokinetic Modelling
A comprehensive pharmacokinetic data set was developed on D5 using both single and
repeated inhalation exposures to D5 at concentrations up to 160 ppm. A single one-hour
inhalation exposure to 10 ppm D5 in humans also was conducted, as were both in vitro and
in vivo percutaneous absorption studies. These data were used to develop PBPK models.
From the point of view of absorption and retention of D5 in the body, there are three
important attributes that control the disposition of this compound. First, it is a volatile
compound with a blood:air partition coefficient (Pb) between 0.3 and 1.0. When Pb is 1.0, half
of the free D5 in venous blood entering the lung would be eliminated by exhalation.
Secondly, it is very soluble in fat. In PBPK models the parameter that determines the
relative fat:blood distribution is the fat: blood partition coefficient (Pf). For this compound, Pf
is somewhere between 600 and 1000, i.e., highly partitioned into lipids in the body. Lastly, it
is rapidly cleared by metabolism, possessing high hepatic clearance. In a single pass through
the liver, 60 to 90% of the free D5 in the blood is removed by metabolism and eliminated via
polar metabolites in the urine. Thus, the pharmacokinetics of this compound is heavily
influenced by an unusual set of properties, high lipid partitioning coupled with very high blood
clearance due to exhalation and metabolism.
In addition, the pharmacokinetics is influenced by the ability of D5 to be retained in blood
lipids and by unusual differences in kinetic behaviour for different dosing routes. Inhalation
and dermal absorption lead to similar pharmacokinetics, presumably since they provide uptake
of molecular forms of the D5. Oral dosing leads to more complex pharmacokinetics that
appears to be associated with uptake of D5 as a micro-emulsion. This behaviour is likely a
reflection of the low water solubility of D5. The overview here focuses on three aspects of D5
pharmacokinetics. The first section describes inhalation and dermal dosing routes. The second
outlines the differences noted with oral dosing with relatively high doses of D5 in gavage
dosing studies. Lastly, it is noted that the combination of properties - high metabolic
clearance and low blood:air partitioning - serve to prevent significant bioaccumulation of this
compounds despite its tendency to be stored in lipids within the body following all routes of
exposure.
Inhalation Exposure
In 6-hr inhalation studies, blood levels of D5 climb rapidly and reach a plateau within a
relatively short time. Although the blood concentrations do not vary very much, fat loading
continues throughout the 6 hour exposure. Only a relatively small amount of the total D5
inhaled is retained, about 10% for a 6 hr exposure and correspondingly smaller percentages
for longer exposure durations. After the major tissues reach steady state, the continued
uptake of inhaled compound would be related to metabolism or continued distribution into fat.
Following inhalation exposure, the measured D5 in blood appears to exist in two pools, a free
pool available for exhalation and metabolic clearance and a sequestered pool, believed to be
associated with blood lipids, that is unavailable for these processes. During inhalation, almost all
D5 in the blood would be in the free pool. Many hours after cessation of exposure when blood
concentrations have fallen by several orders of magnitude from their peaks, the proportion of
total in a bound or sequestered pool becomes much greater.
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PBPK models have also been developed using data obtained from human subjects at the
University of Rochester (Ref. 61). While these data sets are more limited than those
available for rats, the kinetics in humans is controlled by similar processes and the same
conclusions about uptake, tissue loading and blood sequestration of a lipid bound pool
appear equally valid. Although not directly validated by any direct measurements, the time
required to approach steady levels for fat is expected to be 3 or 4 times longer than in the
rats. However, the same concentrations would be reached in each species for a given
exposure regimen in relation to daily exposure patterns (See section 3.4.9 on
bioaccumulation).
Ref. 61 and AR11
Dermal Exposure
During dermal exposures to D5, this chemical is rapidly absorbed into the outer layers of skin,
but it evaporates back out of the skin before significant systemic absorption can occur. In vivo
rat dermal absorption studies showed that ~90% of D5 volatilizes from the skin surface and
that the remaining D5 in the skin at the end of the 24 hr dosing period actually migrates to the
skin surface and continues to evaporate, significantly decreasing the amount remaining in the
skin to 0.03% D5 (Refs. 63, 64). The results of rat or human in vivo dermal absorption studies
are also consistent with human in vitro dermal absorption studies (Ref. 65). Using human
cadaver abdominal skin, only a small amount of the D5 applied to the skin is actually
absorbed (~0.04%). PBPK modelling of the percutaneous absorption data from an in vivo
human dermal absorption study also predicts dermal absorption of D5 to be about 0.05%
respectively (Ref. 62). Of the amount systemically absorbed, ~90% of D5 is exhaled
unchanged. This result appeared contradictory to those obtained for inhalation in that most of
the D5 eliminated from the body after a 6 hour inhalation exposure was as metabolite(s). The
PBPK model for skin absorption (Ref. 62) clarified this discrepancy, showing that all the
processes were in fact consistent between inhalation and dermal exposures. Dermal exposure
traces the uptake of discrete amounts of absorbed D5, showing that most of any amount taken
up into the body is removed by exhalation with a significant first-pass loss from lung due to
venous blood return directly to the pulmonary circulation for oxygenation. The inhalation
exposures integrate processes occurring over the 6 hour period providing for retention of
metabolite during the 6 hour period. As with inhalation exposures, the same conclusions hold
for D5 and the PBPK model for humans requires the same structure to simulate absorption,
distribution and elimination of these compounds in human subjects as were required in
laboratory studies with rats.
Ref. 62 – 65 and AR2
Oral Dosing Routes
Pharmacokinetic studies have also been completed for rats dosed by gavage with D5
dissolved in corn oil. Mass balance of systemic radioactivity indicated ~80% of the
administered dose was excreted unchanged in the faeces. In addition, of the ~20% that
was absorbed 50-60% was eliminated as unchanged D5 in exhaled air and ~20% as water
soluble metabolites in urine. However, the kinetics and tissue distribution observed after this
dose route were qualitatively different from the distributions after inhalation or dermal
exposures. Higher concentrations were noted in liver and spleen than seen previously via the
inhalation and dermal route. The distribution and kinetics differed significantly from
predictions of the PBPK model that successfully described the inhalation and dermal exposure
routes. The dose route differences are most consistent with complications that arise from
different forms of D5 that reach the blood. It appears that the oral route delivers microemulsions that do not readily dissolve into plasma and blood. These micro-emulsions would
be removed from the circulation initially by actions of cells of the reticuloendothelium system,
in liver (where it will be readily metabolized) and spleen. After the oral dosing, it is likely that
uptake may be more associated with lipid transport, such as chylomicron formation and thus
may not be completely available for tissue interactions as free material. In contrast, the kinetics
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and tissue distribution with preferential uptake into fat and body lipids that follows inhalation
and dermal uptake indicate that the D5 is absorbed as a free molecule rather than some
aggregate of D5 and dosing vehicle.
The differences seen after the oral dosing studies compared to inhalation and dermal dose
studies suggested a much higher persistence in blood for oral dosing. However, this apparent
persistence is most likely due to that fraction of D5 in a pool that is unavailable to interact with
tissues and represents the deep blood compartment required to describe all routes of
administration. These dose route differences argue that the oral dose route may have little
relevance for assessing risks of D5 and results from oral studies using oral gavage in corn oil
have to be used with caution for drawing broad conclusions about safety or risks arising from
more common routes of exposure or from oral dosing studies with much lower doses
associated or mixed with feed.
Comment
PBPK models for the cyclomethicone components D5 and D4 have been under development
for several years (Refs. 61 – 65), and have been published now in peer-reviewed journals
[Ref.: AR2, AR11]
PBPK Summary
The pharmacokinetic properties of D5 have been well documented over the past 10 years and
can be described with comprehensive multi-dose-route, multi-species PBPK models. The
pharmacokinetics of this compound is heavily influenced by an unusual set of properties, high
lipid partitioning coupled with very high blood clearance due to exhalation and metabolism. The
more unusual characteristic with this compound is the qualitative differences for
inhalation/dermal routes versus oral route. The former appear to involve absorption of molecular
forms of D5 and the latter appears to involve absorption of micro-emulsions or chylomicrons.
3.4.13.

References for D5 (section 3.4)

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3,1991

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36. Dow Corning Corporation (2005) Decamethylcyclopentasiloxane (D5): A 24-month
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53. Huang, H.-H., S. Marshall and J. Meites (1976) Capacity of Old Versus Young Rats to
Secrete LH, FSH and Prolactin. Biology of Reproduction 14: 538-543
54. Lu, J. K. H., D. A. Damassa, D. P. Gilman, et al. (1980) Differential patterns of
gonadotropin responses to ovarian steroids and to LH-releasing hormone between
constant-estrous and pseudopregnant states in aging rats. Biol Reprod 23: 345-351

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55. Nagaoka, T, M. Takeuchi, H Ónodéra, et al. (1994) Sequential observation of
spontaneous endometrial adenocarcinoma development in Donryu rats. Toxicol Pathol
22(3): 261-269
56. Cooper, R., J. Goldman and G. Rehnberg (1986) Neuroendocrine control of
reproductive function in the aging female rodent. J Am Geriatr Soc 34(10): 735-751
57. Alison, R.H., K.T. Morgan and C.A. Montgomery (1990) Ovary. Pathology of the Fischer
Rat. G. A. Boorman, S. L. Eustis, M. R. Elwell, C. A. Montgomery and W. F. Mackenzie.
San Diego CA, Academic Press: 429-442
58. NDA 17-962: New Drug Application obtained from the Center for Drug Evaluation and
Research, Office of Regulatory Policy, Division of Information Disclosure Policy
59. Burek, J.D., D.H. Patrick, and RJ. Gerson (1988) Weight-of-biological evidence
approach for assessing carcinogenicity. In: Carcinogenicity, HC Grice and JL Cimina
(eds). Springer-Verlag, New York, pp. 83-85
60. Neuman, F., (1991) Early indicators for carcinogenesis in sex-hormone-sensitive
organs. Mutation Research 248: 342-356
61. Reddy, M.B., Looney, R.J., Utell, M.J., Jovanovic, M.L., McMahon, J.M., McNett, D.A.,
Plotzke, K.P., and Andersen, M.E. (2005b) Physiological modeling of the dermal
absorption
of
octamethylcyclotetramethylsiloxane
(D4)
and
decamethylcyclopentasiloxane (D5). Toxicological Sciences, in preparation
62. Reddy, M.B., Dobrev, I.D., Jovanic, M.L., Crofoot, S., McNett, D.A., Tobin, J.M., Utell,
M.J., Morrow, P.E., Plotzke, K.P., and Andersen, M.E. (2005) Physiological modeling of
the inhalation kinetics of decamethylcyclopentasiloxane (D5) in rats and humans.
Toxicological Sciences, in preparation
63. Jovanovic, M., McMahon, J., McNett, D., Tobin, J., Gallavan, R., and Plotzke, K.P.
(2000) In vivo percutaneous absorption of 14C-octamethylcyclotetrasiloxane in Fischer
344 rats. Toxicologist 2000, 54(Suppl.), 148 (Abstract)
64. Jovanovic, M, McMahon, J., McNett, D., Tobin, J., Gallavan, R., and Plotzke, K.P. (2004)
In vivo percutaneous absorption of 14C-decamethylcyclopentasiloxane in Fischer 344
rats. Toxicologist 2004 (Abstract)
65. McMahon, J.M, Plotzke K.P., Jovanovic, M.L,. McNett, D.A, Galavan, R.H., and Meeks,
R.G. (2000) In vitro absorption of decamethylcyclopentasiloxane (D5) in human skin: a
comparison to octamethylcyclotetrasiloxane (D4). Toxicologist 2000, 54(S-1):14
(Abstract)
66. SEHC, CES, SIAJ. Decamethylcyclopentasiloxane (D5): A White Paper on Health
Research Findings. June 2005
Additional References added by SCCS
AR1. Jovanovic M.L., McMahon JM, McNett DA, Tobin JM, Plotzke KP (2008) In vitro and In
vivo percutaneous absorption of 14C-octamethylcyclotetrasiloxane (14C-D4) and 14Cdecamethylcyclo-pentasiloxane (14C-D5). Regul Toxicol Pharmacol. 50: 239–248.
AR2. Reddy M.B., Looney RJ, Utell MJ, Plotzke KP, Andersen ME. (2007) Modeling of human
dermal
absorption
of
octamethylcyclotetrasiloxane
(D4)
and
decamethylcyclopentasiloxane (D5). Toxicological Sciences 99(2): 422–431.
AR3. Crofoot SD, Stanton E, Siddiqui W, Zimmer MA (1990) A 14-day subchronic gavage
study with decamethylcyclopentasiloxane in rats. Unpublished data, submitted by
SEHSC to Cosmetic Ingredient Review Expert Panel [cited in AR14]
AR4. Siddiqui WH, Stump DG, Reynolds VL, Plotzke KP, Holson JF, Meeks RG. (2007b) A
two-generation reproductive toxicity study of decamethylcyclopentasiloxane (D5) in
rats exposed by whole-body vapor inhalation. Reprod Toxicol. 23(2): 216-225.
AR5. Environ International Corporation. 2006. Evaluation of exposure to D5 for consumers,
workers and the public. Prepared for the Silicones Environmental Health and Safety
Council. [cited in OEHHA 2007].
AR6. Tobin JM, McNett DA, Durham JA, Plotzke KP. (2008) Disposition of decamethylcyclopentasiloxane in Fischer 344 rats following single or repeated inhalation exposure
to 14C-decamethylcyclopentasiloxane (14C-D5). Inhal Toxicol 20(5): 513-531

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AR7. Varaprath S, McMahon JM, Plotzke KP (2003) Metabolites of hexamethyldisiloxane and
decamethylcyclopentasiloxane in Fischer 344 rat urine--a comparison of a linear and a
cyclic siloxane. Drug Metab Dispos. 31(2): 206-214
AR8. Quinn AL, Regan JM, Tobin JM, Marinik BJ, McMahon JM, McNett DA, Sushynski CM,
Crofoot SD, Jean PA, Plotzke KP (2007a) In vitro and in vivo evaluation of the
estrogenic, androgenic, and progestagenic potential of two cyclic siloxanes. Toxicol Sci.
96(1): 145-153
AR9. Bin H, Rhodes-Bower S. et al. (2003). Octamethylcyclotetrasiloxane exhibits
estrogenic activity in mice via ERα. Toxicol. Appl. Pharmacol. 192: 254-261.
AR10. Dow Corning Corporation. (2005b) Non-regulated study: effect of cyclic siloxanes on
dopamine receptor regulation of serum prolactin levels in female Fischer 344 rats. 54
pp. (cited in OEHHA 2007; not submitted to SCCP/S)
AR11. Reddy MB, Dobrev ID, McNett DA, Tobin JM, Utell MJ, Morrow PE, Domoradzki JY,
Plotzke KP, Andersen ME (2008) Inhalation dosimetry modeling with decamethylcyclopentasiloxane in rats and humans. Toxicological Sciences 105(2): 275–285.
AR12. OEHHA (2007). Toxicity Data Review: Decamethylcyclopentasiloxane (D5).
September
13,
2007.
Available
at:
www.oehha.ca.gov/multimedia/biomon/pdf/1208cyclosiloxanes.pdf
AR13. Ministers of the Environment and of Health, Canada. Screening Assessment for
Decamethylcyclopentasiloxane (D5). November 2008
AR14. Cosmetic Ingredient Review (2009) Amended Final Report of the Cosmetic Ingredient
Review Expert Panel of the Safety Assessment of Cyclomethicone, Cyclotetrasiloxane,
Cyclopentasiloxane, Cyclohexasiloxane, and Cycloheptasiloxane. Dezember 8, 2009
3.5.

Discussion

3.5.1.

Discussion on D4 (Octamethylcyclotetrasiloxane; Cyclotetrasiloxane)

The reference numbers given in this chapter refer to the D4 references listed in chapter 3.3.13.
Physico-chemical properties
Octamethylcyclopentasiloxane (D4) is a clear, colourless synthetically derived silicon-based
fluid with a molecular weight of 296 Daltons. It is used in cosmetics with a wide range of
concentrations as well as in a variety of other applications.
Skin/eye irritation and sensitisation
According to rather old non-GLP studies, cyclomethicone appears not to be irritant to skin or
mucous membranes. A GLP study performed according to OECD guideline demonstrated
that cyclomethicone is not a skin sensitiser.
Dermal absorption
Several in vivo and percutaneous absorption studies with D4 have been performed with
some variation in results. In vitro an average of 0.5% of octamethyltetracyclosiloxane (D4,
applied neat or in antiperspirant formulation containing 62% (w/w) D4 was absorbed in
human cadaver skin and the receptor fluid after 24 h of exposure, with dermal absorption of
0.94% of the applied dose as an upper value (Ref. 19). Lower values were found in an in
vitro study with pig skin, where dermal absorption of 14C-D4 was maximum 0.05% from the
three formulations and different concentrations tested (Ref. 80). Similar to in vitro studies
with human or pig skin, also the in vivo rat study demonstrated that the majority (~90%)
of D4 applied volatilized from the skin surface before being absorbed. On average less than
1.0% of applied D4 appeared to be absorbed in vivo, with the majority remaining in the
skin. Consistent with in vitro results for human cadaver skin, pharmacokinetic modelling of
dermal absorption in human volunteers (AR 13) indicated that 0.12% and 0.30% of applied
D4 was absorbed into systemic circulation for men and women, respectively.
A value of 0.5% for dermal absorption of D4 is taken for the safety assessment of D4.

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Pharmacokinetics
Radiolabelled octamethyltetracyclosiloxane (D4) is rapidly absorbed orally when
administered in corn oil, with tissue levels generally following plasma levels over time. The
same pattern of disposition of radioactivity was seen with neat D4 or Simethicone, but the
oral absorption and transit times in gastrointestinal tract were altered. This study indicated
that the oral absorption of D4 can be significantly influenced by the vehicle/carrier used to
deliver D4.
When inhaled, approximately 5% D4 in rat and 12% D4 in humans is absorbed. High D4
levels were found in lung tissue and fat as compared to other tissues. This could be
expected, as D4 is lipid soluble and would preferentially deposit in fat and highly lipophilic
tissues. There is evidence that D4 accumulates in adipose tissue; the toxicological relevance
of this is unknown.
Pharmacokinetics as well as PBPK modelling has revealed that 80% of the systemically
available dose is exhaled. Possibly a certain percentage of the dermally absorbed dose is
eliminated in exhaled air as the venous blood passes through the lung. This can lead to a
reduction in the amount of D4 in the arterial blood delivered to a target organ and may
result in a somewhat lower actual systemic dose than calculated on the basis of dermal
absorption alone.
Mutagenicity
The negative results obtained in bacteria (reverse mutation assay) or in mammalian cells,
i.e. in vitro chromosomal aberration and SCE test, along with an in vivo micronucleus assay
and dominant lethal test, indicate that D5 does not possess mutagenic or genotoxic potential.
Toxicity
D4 has been extensively evaluated for its safety in a full range of toxicity studies by a
number of routes of exposure. The results of these studies show that D4 has a very low
acute oral, inhalation and dermal toxicity. Repeated dose studies at relatively high oral and
inhalation doses revealed few systemic effects. In repeated-dose studies, clinical signs of
toxicity were minimal and the histological changes observed were reversible. One consistent
finding was a reversible liver enlargement (hypertrophy) and phenobarbital-like increases in
xenobiotic metabolising enzyme activities.
D4 was a mild irritant to the respiratory tract when inhaled. A major adverse effect seen
with D4 has been evidence of reproductive toxicity in rats. These effects consist of
reductions in corpora lutea, implantation sites and number of pups born to dams exposed to
high concentrations of D4, and are all inter-related. Mechanistic research in female rats
indicates that suppression of the preovulatory luteinizing hormone surge could cause the
delayed ovulation stage and reduced fertility (see below).
For D4, appropriate pivotal studies to define a meaningful NOAEL are considered to be the
three 90-day repeat-dose studies in rats (Ref. 13, 14, 15) together with the reproduction
toxicity studies in rats (Ref. 34; AR 14) and a combined chronic/carcinogenicity study (Ref.:
37; AR 4). These inhalation studies were conducted with the 90-day study in Sprague
Dawley rats (Ref. 14) and the two-generation study in SD rats (Ref. 34) using 7 days per
week exposure to D4, and 5 days per week in the chronic 2 year study (Ref.: 37; AR 4).
Data from other animal species (mice, guinea pig, rabbit, hamster) and other routes of
administration (dermal, oral) are insufficient and/or inappropriate for D4 risk assessment.
In the pivotal studies, the NOAELs were largely determined by the three organ toxicities,
which have morphological counterparts i.e. liver, respiratory tract and ovary. The NOAELs
for general and reproduction toxicity in the 90-day repeat-dose studies in rats and the twogeneration reproduction toxicity study in rats can reasonably be set at 300 ppm. The results
of the other repeated-dose toxicity studies (up to 13 weeks duration) and the onegeneration reproduction toxicity studies do not conflict with this conclusion regarding
reprotoxicity. Yet, the number of corpora lutea was decreased at 300 ppm, and increases in

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liver and kidney weights were also noted at 300 ppm in the latter study. Thus, 300 ppm
could be considered a LOEC rather than a NOAEL.
The main toxicities are viewed differently in terms of their importance in safety assessment
and in setting NOAELs as discussed below.
The liver weight increase with centrilobular hepatocyte hypertrophy has been attributed to
a “phenobarbital-like” induction of rat hepatic CYP enzymes (Ref. 57, 58). This change was
reversible (Ref. 13, 14, 15) and was not associated with overt hepatotoxicity, i.e.
morphological evidence of necrosis/degeneration or increases in hepatic serum enzymes.
Mild enzyme induction is considered to be an adaptive response to xenobiotics and has no
significant impact on determining NOAELs or on human risk assessment. Indeed, D4 in the
24-month combined chronic/oncogenicity inhalation rat study (doses 0, 10, 30, 150 or 700
ppm) did not induce hepatic tumours but hepatic hypertrophy (see Section 3.3.7).
The respiratory tract changes in the nose and lungs are considered to be adaptive
responses to a mild, non-specific irritant. Again, this change was reversible (Ref. 15).
Considering that rats were exposed to D4 for 6 hours/day for at least 5 days/week for the
duration of the various studies, the magnitude of the response was minute. When one
further considers that the application route for cosmetics is primarily dermal, then rat
respiratory tract changes can be largely discounted in determining NOAELs for safe human
use of D4. In the 24-month combined chronic/oncogenicity inhalation rat study, D4 appears
to be devoid of respiratory tract effects.
Exposure to D4 produced some effects on the thymus. Few studies in the provided dossier
examined the thymus. The results were equivocal; seeming not to be species or sex related
and occurred with oral and inhalation exposure in rat and rabbit. In two short term (28 day)
studies, reduced thymus weights were marked (Ref. 10, 15). In the 2-generation rat study,
no significant changes were noted in F1 and F2a animals (Ref. 34). In nose only inhalation
pharmacokinetic studies in rats (Ref. 36, 38), the AUC and Cmax values were highest in fat,
mid range in liver, thymus, lungs and nasal mucosa, and lowest in the reproductive organs.
Elimination was relatively slow in these tissues (t1/2 >168 h). No immunological effects in
humans were seen in the study provided (Ref. 56). It would be interesting to know if there
is more data as this could be a possible indicator of altered immune response.
The mechanism for delayed ovulation status resulting in reduced fertility has been studied.
The observed changes were shown to be reversible (Ref. 32, 33). Other studies have shown
that D4 has very weak estrogenic and anti-estrogenic activity in a Rat Uterotrophic Assay in
both immature Sprague Dawley and F344 rats. D4 was 77,000 to 25 million times less
potent than ethinyloestradiol or diethylstilbestrol in Sprague Dawley or Fischer 344 rats
(Ref. 69). Many observations in the reproductive studies (Ref. 27 – 32) are inconsistent
with a significant estrogenic and anti-estrogenic activity, thus indicating the very weak
hormonal potency of D4. In a series of studies in mice, in which D4 was administered
orally, D4 significantly reduced serum estradiol levels (Ref. 70). On the other hand, uterine
peroxidase activity, a marker for estrogenic activity, and uterine weights were significantly
increased. The uterotrophic effects of D4 were ablated by pre-treatment with ICI 182,780,
an estrogenic receptor (ER) antagonist, and ovariectomised αER knock-out mice showed no
increases in uterine weights when treated with D4. It can be concluded that D4 exhibits
estrogenic activity in mice via ERα, probably by direct receptor binding. The data also
indicate that the stimulatory effect of D4 on the uterus is not related to (endogenous)
estradiol activity.
Rather than a direct (ER) receptor mediated mechanism, an indirect mode of action appears
to be more relevant for explaining the reproductive toxicity and carcinogenicity of D4
observed at high doses: There are data in rats indicating that D4 can cause a delay or
blockage of the luteinizing hormone (LH) surge necessary for optimal timing of ovulation.
Barbiturates given during a critical time period, which is about seven to eight hours before
the LH release on the day of proestrus, can block or delay the LH surge and delay ovulation
93

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for 24 hours (Ref. 71). The extent of the decrease in ovulation is time- (Ref. 71, 72) and
dose-dependent (Ref. 72, 73). Repeated administration of barbiturates during this critical
period on subsequent days continues to suppress the LH surge and consequently ovulation.
A similar mechanism could provide an explanation for the reduced fertility rate encountered
in the female groups exposed to D4 for one to three days prior to mating (Ref. 33). Initial
support for this mechanism was obtained by exposing ovariectomized Sprague Dawley rats
with a subcutaneous implant of estradiol to inhaled D4. Several animals had reduced LH
levels at the peak time (Ref. 74). In a well designed follow-up study, definitive support of
the role of LH was obtained from a study of estrous cycle staged female Sprague Dawley
rats exposed to 700 or 900 ppm D4 for 6h/day for 3 days, i.e. on diestrus 1, diestrus 2, and
pro-oestrus. Measurement of LH on the day of pro-estrus at 2, 4, 6, 8 and 10 p.m. showed
a significant reduction of LH levels at 4, 6 and 8 p.m. which correlated with blocked
ovulation (Ref. 75). The majority of reproduction findings in the two-generation study are
also consistent with a long-term suppression of LH release.
The NOAEL of 300 ppm for reproductive toxicity of D4 is higher than the NOAEL of 150 ppm
derived from the chronic/carcinogenicity studies (below).
Carcinogenicity
A 2-year combined chronic/carcinogenicity study was conducted by whole body vapor
inhalation of D4 in Fischer 344 rats. Changes were identified at the highest exposure
concentration (700 ppm) only, and included increases in kidney weights associated with
chronic nephropathy, increases in mean uterine weight and uterus-to-body weight ratios, an
increase in cystic endometrial hyperplasia, and an increased incidence of uterine
endometrial adenomas (Ref. 37, submission II). An earlier onset and increased incidence of
mononuclear cell leukaemia (MNCL) was observed in male rats, not in exposed female rats.
Since this tumour type is unique to F344 rats, its relevance to humans is questionable.
A NOAEL of 150 ppm was identified in this study based on endometrial adenomas. Since D4
is not genotoxic, an epigenetic mode-of-action was considered to be responsible for its
neoplastic effect. Special studies (section 3.3.12) conducted to understand the mode-ofaction in the chronic study support a secondary effect rather than a direct effect of D4 on
the uterus: It is unlikely that D4’s very weak estrogenic activity can account for the effects
seen in this study. Rather, the data support the conclusion that D4 can act as a dopamine
agonist causing a reduction in prolactin. A reduction of prolactin in the rat then causes
luteolysis and new ovarian follicle stimulation resulting in estrogen dominance, which leads
to persistent endometrial stimulation and finally to uterine tumours. However, it is
important to point out that prolactin is not luteotropic in primates and humans (Ref. 27,
28).
On the other hand, from the reproductive studies (section 3.3.8) it is possible that D4 could
affect LH secretion from the pituitary, which would also result in elevated endogenous
estrogen as a consequence of prolonged stimulation of tissues of ovarian origin.
While it is possible that D4 can affect the secretion of LH in female F344 rats in a manner
similar to that observed for SD rats (AR 21), it is also possible that the mode of action for
the cystic endometrial hyperplasia and endometrial adenomas observed in the combined
chronic/carcinogenicity study is by effects on prolactin through interaction with the
dopamine receptor in the pituitary. This view is supported by as yet unpublished studies in
vitro and in vivo indicating that D4 can inhibit prolactin release from the pituitary by acting
as a dopamine agonist (AR 5).
In conclusion, the uterine (endometrial) adenomas and hyperplasia observed at the highest
dose level of 700 ppm in a lifetime study in rats are due to threshold effects on the rat
endocrine system. This view is supported by the lack of genotoxic potential. On the other
hand, there is at present insufficient (published) data to dismiss altogether the proposed
neuroendocrine mode of action in rats as not relevant for humans.
In the final safety assessment of cyclomethicone (3.6), effect levels were selected/chosen
that cover the most relevant toxicities observed for both D4 and D5.
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3.5.2.

Discussion on D5 (Decamethylcyclopentasiloxane; Cyclopentasiloxane)

The reference numbers given in this chapter refer to the D5 references listed in chapter 3.4.13
Physico-chemical properties
Decamethylcyclopentasiloxane (D5) is a clear, odourless, synthetically derived silicon-based
fluid with a molecular weight of 371 Daltons. It is used in cosmetics with a wide range of
concentrations as well as in a variety of other applications.
Skin/eye irritation and sensitisation
Tests with D5 provided no evidence that it is irritant to skin or mucous membranes or that it
is a skin sensitiser.
Dermal absorption
In vitro studies using rat and human skin and in vivo studies in rats and humans have
shown very low dermal absorption rates of ≤ 0.1% to 0.17% for D5 (AR1) Furthermore, PBPK
modelling of the percutaneous absorption data predict dermal absorption of D5 to be about
0.05%. The PBPK models also show that about 90% of the small amount of systemically
absorbed D5 is eliminated by exhalation within 24 hours (AR2).
Mutagenicity/genotoxicity
The negative results obtained in the bacterial reverse mutation test, in vitro chromosomal
aberrations in Chinese Hamster V79 cells, and in vivo unscheduled DNA synthesis and
micronucleus assays indicate that D5 does not possess mutagenic or genotoxic potential.
Toxicity
D5 has a low acute oral and inhalation toxicity in rats. No overt toxicity occurred following a
single oral dose of 4800 mg D5/kg bw (Ref. 1). The inhalation LC50 was 8.67 mg/l air (560
ppm) with the lungs as the target organ of toxicity (Ref. 2).
Dermal application to rats of up to 1600 mg D5/kg bw for 28 days did not produce any test
material related effects (Ref. 9).
Oral studies for 14 and 28 days at dose levels up to 1600 mg D5/kg/day revealed liver
weight increases in Sprague Dawley rats, and a LOEL of 100 mg/kg bw/day (Ref. 4). Test
material related effects on liver weight were also found in Wistar rats administered between
100 up to 1000 mg D5/kg bw by oral gavage for 13 weeks (Ref. 5). No significant
histopathological effects related to D5 exposure were seen.
Three whole-body inhalation studies of four weeks in Fischer 344 rats (two studies; Refs. 6,
7) or Wistar rats (one study, Ref 8), at doses up to 197 ppm were conducted. In the Fischer
344 rats, there was an increased incidence of goblet cell proliferation in the nasal cavity and
minimal interstitial inflammation in the lungs, which is consistent with exposure to a mild
respiratory irritant. Increases in absolute and relative liver weight also were seen which were
accompanied by slight hepatocellular hypertrophy. These effects were reversible upon
cessation of treatment. In Wistar rats, there was an increase in relative liver weight in male
and female rats. All other effects were considered unrelated to D5 exposure.
One nose-only vapour inhalation study of 90 days duration in Fischer 344 rats at exposure
concentrations up to 233 ppm (Ref. 11) and one 90-day whole body inhalation study in
Sprague-Dawley rats at exposure concentrations up to 120 ppm (Ref. 12) were conducted.
Male and female Fischer 344 rats had a significant increase in absolute and relative liver
weight, and a dose-related increase in gamma glutamyltransferase could be observed in
females only. Possible treatment related histopathological findings included an increased
incidence of ovarian interstitial gland hyperplasia and vaginal mucification and atrophy in
female rats at 233 ppm. In Sprague-Dawley rats at the end of 90 days of exposure to 120
ppm, there was an increase in relative liver weight, which had returned to normal in females at
the end of 28 days of recovery.

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Reproductive toxicity
In both, one- and two-generation studies (Refs. 25, 26) with male and female SpragueDawley rats there were no significant effects on any of the parameters examined upon
exposure by whole-body vapour inhalation to D5 up to 160 ppm. Moreover, in vivo rat
studies with short-term inhalation exposure to D5 showed no increase in uterine wet or
blotted weights and no increase in male reproductive organ weights. In vitro, D5 did not
bind to human estrogen receptors α and β or progesterone receptors and was negative in
ERα and ERβ reporter gene assays. On the other hand, in a nose-only inhalation study of 90
days duration in Fischer 344 rats, treatment-related histopathological findings included an
increased incidence of ovarian interstitial gland hyperplasia and vaginal mucosal mucification
and atrophy in the female rats exposed to 233 ppm, and a slight, not statistically significant,
decrease in ovaries and testes weight of the animals.
In conclusion, a NOAEL of 160 ppm for reproductive toxicity of D5 is appropriate.
In the two-generation study, a statistically significant increase in the incidence of pulmonary
vascular mineralization was observed in all F0 and F1 animals at 30 ppm and above. Also,
increased incidences of minimal alveolar histiocytosis were observed at the high
concentration (160 ppm) in F0 and F1 females, consistent with exposure to a mild irritant.
When one further considers that the application for cosmetics is primarily dermal, then rat
respiratory tract changes can be largely discounted in determining NOAELs for safe human
use of D5.
Carcinogenicity
In the two-year combined chronic/carcinogenicity study (Ref. 36), exposure to D5 caused
uterine endometrial adenocarcinomatous polyps and adenocarcinomas. From additional
evaluations of the mode of action for this effect in the uterus, there are indications that D5
might act, as also suggested for D4, as a dopamine agonist and thereby affects prolactin
secretion in the rat. The relevance of this mode of action in humans is unclear at present.
The lack of genotoxic effects for D5 (based on limited genotoxicity data) suggests that the
uterine tumours observed in the chronic toxicity/carcinogenicity study could be due to
threshold effects.
In the final safety assessment of cyclomethicone (3.6), effect levels were selected/chosen
that cover the most relevant toxicities observed for both D4 and D5.
3.6. Safety assessment of D4 and D5
Toxicities
D4 and D5 exert a rather similar profile of toxicities. Since the two compounds are
apparently used together in cosmetic products in varying proportions, the SCCS has decided
to perform a combined risk assessment for the two compounds. For the safety evaluation,
SCCS has considered the available database, and derived the following critical effect levels:
a NOAEL of 150 ppm from chronic studies with inhalation exposure and a LOEL of 100
mg/kg bw/d from subchronic toxicity studies with oral exposure. These values should also
cover some possible differences in potency between D4 and D5.
The NOAEL for reproductive toxicity of D4 in rats in the 2-generation study was defined as
300 ppm (Siddiqui et al. 2007a). The NOAEL for D5 in the 2-generation rat study was 160
ppm, i.e. the highest concentration that can be applied without aerosol formation (Siddiqui
et al 2007b).
In chronic toxicity studies, D4 caused endometrial adenomas only at 700 ppm; the NOAEL
was 150 ppm (Dow Corning 2004). D5 induced endometrial adenocarcinomas only at 160
ppm (Dow Corning 2005). Other non-neoplastic effects (e.g. liver weight increases) were
observed at 150 ppm D4 and 160 ppm D5 in these studies.

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Effects on liver were also observed in subchronic toxicity studies with D4 and D5, with either
inhalation exposure or oral administration: The oral LOEL for liver weight increase with D5
in rats was 100 mg/kg bw/d (Jäger & Hartmann 1991), which for D4 in rats and rabbits was
500 mg/kg bw/d (Dow Corning 1986). Liver weight increases in mature rats after oral D4
dosing, and decreased fetal body weights and liver to body weight ratios after one week of
administration to pregnant rats indicate a LO(A)EL of 100 mg/kg bw/day for D4 (Falany & Li
2005). Liver weight increases after subchronic inhalation of D4 or D5 (≥ 35 or 46 ppm)
were reversible upon cessation of exposure (Burns-Naas et al. 2002, Burns-Naas et al.
1998).
Other systemic effects, such as increases in hepatic CYP enzymes have been reported at
relatively low concentrations of D4 or D5 (≥ 30 ppm), but are considered as adaptive
responses.
Local effects, such as goblet cell proliferation in the nasal cavity and minimal alveolar
histiocytosis (pulmonary vascular mineralization) can be related to a mild irritant effect of
D4/D5 and were not considered for safety calculations.
In conclusion, a NOAEL of 150 ppm is chosen with regard to the most critical effects of
cyclomethicone in rats, namely reproductive toxicity and potential carcinogenicity, and a
LOAEL of 100 mg/kg body weight to cover organ weight changes in liver, kidney and
thymus.
Exposure
Use levels of Cyclomethicone in cosmetic products
Cyclomethicone is used in various cosmetic products as an antistatic / emollient /
humectant / solvent / viscosity controlling / hair conditioning ingredient and for the good
spreadability of the products. The applicant had initially described that cyclomethicone
(octamethyltetracyclo-siloxane, D4) is used in all cosmetic products at an average
concentration of 1%. However, published data in the scientific literature indicated that
cyclomethicone may be present in some cosmetic products, for instance in antiperspirants,
at concentrations >40% concentration. The SCCP (2004) requested clarification from
COLIPA on typical use patterns and concentrations. The response (provided in a letter to
SCCP) was not sufficiently detailed. Therefore, the SCCS considered information provided by
the Norwegian authorities (Talberg 2006) and the Danish EPA (2005) on use concentrations
and relevant subgroups of cosmetic products. This and recent surveys on organosilicone
compounds in personal-care and household products (Horii & Kannan 2008; Wang et al.
2009; CIR 2009) indicate the presence of both D4 and D5 in several cosmetic products.
Thus, it is indicated to assess the safety of cyclomethicone by considering exposure to both
compounds.
Table 11: Concentration of D4 + D5 in different types of cosmetic products
according to Norwegian report [Talberg 2006]
The information on D4 and D5 concentrations was taken from the American branch
periodical Cosmetic & Toiletries Magazine (C&TM) that regularly provides formulations for
many different types of cosmetics
Type of product

Average
concentration (%)
7.2

Range (%)

Sun protection products (SPP)

Number of product
within group
25

Skin care products (SCP)

5.7

1 – 16.5

SPP and SCP combined

6.6

Hair styling products

2.0

1-5

Hair care (not colours)

14.2

3 -28

0.5 - 24

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________
Hair care combined

8.1

Rouge, powder

9.9

2 – 33.6

Deodorants and antiperspirants

8 - 45

All product

8.3

The SCCS used the reported average concentration (8.3 %) of D4 and D5 in cosmetic
products (Ref. Talberg) to calculate the systemic exposure resulting from dermal absorption
(see below) for different types of products.
It is worth noting that cyclomethicone (D4 and/or D5) is not present in all cosmetic
products: The Danish EPA has a database in which 766 cosmetic products are registered
with respect to their chemical content: 61 products (8% of these) contain D4 or
cyclomethicone (D4 and/or D5) (http://www.mst.dk/NR/rdonlyres/13C1D483-54CE-48BCB281-5F51EBCF7460/0/engudgavelayout.pdf). These are hair styling products, shampoos,
conditioners and stick deodorants (Lassen et al. 2005). Another database (Skin Deep),
established by the American environmental organisation the Environmental Working group,
lists 14900 cosmetic products and their ingredients. According to this database 719
products contain cyclomethicone, and 964 products contain D5), that is about 11% of all
cosmetic products (cited from Talberg). Data published in the recent final report of the
Cosmetic Ingredient Review Expert Panel (CIR 2009) support similar conclusions on use
patterns in various product categories. For example, D5 is reportedly used in 60 out of 499
mascara products, suggesting that about 12% of mascara products on the market contain
cyclomethicone (Tab. 3 in CIR 2009).
Dermal absorption
Experimental studies showed a low absorption of D4 and D5. Despite some variation in the
results of in vitro and in vivo studies with the compounds, it is apparent that dermal
absorption of D5 is lower than that of D4. The majority (~90%) of cyclomethicone applied
to human skin in vitro and rat skin in vivo, volatilized from the skin surface before being
absorbed. In vitro an average of 0.5% of D4, applied neat or in antiperspirant formulation
containing 62% (w/w) D4 was absorbed in human cadaver skin and the receptor fluid after
24 h of exposure. For D5 comparable in vitro studies showed an average of 0.04% dermal
absorption. In rat studies on average less than 1.0% of applied D4 and between 0.1 to <1%
of applied D5 were absorbed in vivo, with the majority remaining in the skin.
Pharmacokinetic modelling of dermal absorption in human volunteers indicated that 0.12%
and 0.30% of applied D4 was absorbed into systemic circulation for men and women,
respectively; for D5 it was 0.05% for both sexes.
In the following calculations dermal absorption of cyclomethicone (D4 plus D5) in the
products has been considered as 0.5% of the applied dose, and only single application per
day has been considered.
The value of 0.5%, taken for both components, is considered a conservative approach:
Since the ratios of D4 and D5 in cosmetic products are unknown, dermal absorption of
cyclomethicone is calculated with the average experimental D4 value (0.5%) that is in
accordance with PBPK modelling for D4 indicating dermal absorption of 0.3% in females. In
comparison, a value of 0.17% (the highest experimental value reported) for dermal
absorption of D5 was taken by the Canadian authorities in 2008, based on the publication
by Jovanovic et al. (2008).

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

Calculation of systemic exposure dose (SED) from all cosmetic products excluding
sun protection products and oral products
Applied amount (17.8 g – oral 3.5 g)
Average concentration
Dose cyclomethicone
Dermal absorption
Cyclomethicone absorbed
Typical human body weight:
SED (14.3*103 mg/day * 8.3/100 * 0.5/100) / 60 kg

=
=
=
=
=
=
=

14.3 g/day
8.3 %
1.2 g/day
0.5 %
6 mg/day
60 kg
0.1 mg/kg bw/day

Calculation of systemic exposure dose (SED) from sun protection products
Applied amount
Average concentration
Dose cyclomethicone
Dermal absorption
Cyclomethicone absorbed
Typical human body weight:
SED (18*103 mg/day * 7.2/100 * 0.5/100) / 60 kg

=
=
=
=
=
=
=

18.0 g/day
7.2 %
1.3 g/day
0.5 %
6.5 mg/day
60 kg
0.1 mg/kg bw/day

Calculation of SED (rat) at the NOAEL
Converting ppm concentrations to a systemic dose following inhalation exposure requires
the respiratory minute volume and the % of the inhaled dose absorbed.
NOAEL:
Conversion factor:
Combined conversion factor:
Converted NOAEL:

150 ppm (exposure 6 hours, 5 days per week)
1 ppm = 0.012 mg/l (D4) and 0.015 mg/l (D5)
1 ppm = 0.0135 mg/l
150 ppm = 0.0135 mg/l x 150 = 2.0 mg/l
(exposure 6 hours, 5 days per week)

Inhalation volume1, male rat
Weight male rat:
Exposure by inhalation, male rat:
[(2.0 x 20.5 x 6) x 5/7]/0.5
Absorption by inhalation, rat
NOAEL male rats (356 x 0.05)

20.5 l/h;
0.5 kg;

Inhalation volume female rat
Weight female rat:
Exposure by inhalation, female rat
[(2.0 x 15.7 x 6) x 5/7]/0.35
Absorption by inhalation, rat
NOAEL female rats (389 x 0.05)

356 mg/kg bw/day
5%
17.8 mg/kg bw/d
15.7 l/h
0.35 kg
389 mg/kg bw/day
5%
19.5 mg/kg bw/d

Default inhalation values for rat from REACH (chapter R.8 – Dose p. 70)

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

Calculation of the Margin of Safety (MoS) from cosmetic products excluding sun
protection products and oral products, based on inhalation studies
Systemic exposure dose (SED)
NOAEL (inhalation, male rats):=

=
=

0.1 mg/kg bw/day
17.8 mg/kg bw/day

Margin of Safety

NOAEL / SED =

178

Calculation of the Margin of Safety (MoS) from cosmetic products (excluding oral
products) and sun protection products, based on inhalation studies
Systemic exposure dose (SED) human
NOAEL (inhalation, male rats):

=
=

0.2 mg/kg bw/day
17.8 mg/kg bw/day

Margin of Safety

NOAEL / SED =

Comment
If MoS calculations were based on the LOAEL of 100 mg/kg bw/day from oral studies,
adjusted for 52% oral absorption and a factor of 3 for converting the LOAEL to a NOAEL, the
MoS for all cosmetic products (excluding sun protection and oral care products) would be
173; the MoS for cosmetic products including sun protection products (excluding oral care
products) would be 87. These values are very similar to the figures calculated on the basis
of a NOAEL of 150 ppm from inhalation studies.
In this particular case SCCS considers calculated MoS values <100 for an exposure scenario
that includes also sun protection products with cyclomethicone acceptable for the following
reasons: (i) sun protection products are not regularly used. (ii) Recent surveys on product
uses and cyclomethicone concentrations show that D5 is now used in a higher proportion of
products than D4 (Talberg 2006; CIR 2009; Hori & Kannan 2008). (iii) The SED calculation
is based on a value for dermal absorption which overestimates D5 absorption.
Uncertainties
There are considerable uncertainties in exposure estimates due to wide range of D4/D5
levels present in various cosmetic products (and frequency of use per day). Thus, external
exposure may differ from that based on average concentration values. Current data indicate
the use of cyclomethicone at concentrations between 0.06 to 89% in a total of 1499
products (CIR 2009). An estimated 10% of products on the market contain cyclomethicone,
and some product categories are more important for the overall exposure than others. A
conservative estimate of exposure is made by assuming that all products in the relevant
product categories contain cyclomethicone, rather than a fraction of these.
The actual systemic dose might be somewhat lower than calculated since a certain
percentage of the dermally absorbed dose (SED) is eliminated in exhaled air as the venous
blood passes through the lungs. Moreover, the SED for combined human exposures to D4
and D5 is based on the average value of 0.5% dermal absorption for D4 as conservative
approach, since information on the proportion of D4/D5 in various product categories was
not available.
The margin of safety calculation for cyclomethicone further depends upon the critical effect
level derived from animal studies with D4 and/or D5. As explained in section 3.6, SCCS has
chosen a NOAEL of 150 ppm based on chronic inhalation studies with D4 and D5, and a
LOEL of 100 mg/kg bw/day from subchronic oral studies with D5, taking into account similar
uses and function of D4 and D5, and their similar profile of toxicities in the animal studies
(section 3.5.1 and 3.5.2). Critical effects of the compounds covered by the NOAEL of 150
ppm include carcinogenicity as well as reproductive toxicities. It is recognized that both are
100

SCCS/1241/10
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___________________________________________________________________________________________

due to a mode of action that is thresholded. On the other hand, there is at present
insufficient (published) data to dismiss altogether the proposed mode of action in rodents as
not relevant for humans.
Non-neoplastic changes in chronic inhalation and reprotoxicity studies with D4 included
increases in liver and kidney weights >150 ppm, and a decreased number of corpora lutea
at 300 ppm. Thus, 300 ppm could be considered a LOEC rather than a NOAEL.
Other systemic effects observed at lower exposure levels of D4 and D5, namely increases in
hepatic CYP enzymes, are considered as adaptive responses. Liver weight increases after
subchronic inhalation of D4 and D5 (≥ 35 or 46 ppm) were reversible upon cessation of
exposure. Local effects, such as goblet cell proliferation in the nasal cavity and minimal
alveolar histiocytosis (pulmonary vascular mineralization) can be related to a mild irritant
effect of D4/D5 and were not considered for safety calculations. The applicant noted that
this is justified, considering that consumer exposure to cyclomethicone containing cosmetic
products is mainly dermal, and that particle size in hair spray products (≈ 38 µm in aerosol
hair sprays and >80 µm in pump hair sprays) is large, compared to respirable particulate
sizes (<10 µm) [CIR 2009]. The SCCS notes that these particle sizes refer to mean particle
sizes, but both the aerosol and pump sprays generate particles with a certain distribution in
particle size. For the pump sprays it is accepted that the inhalable fraction is negligible.
Aerosol hair sprays however, will result in a small fraction of respirable particles. Given the
(only) mild irritant effect of D4 and D5 in combination with a very short exposure duration
there is no need for a separate risk assessment for D4/D5 in spray applications.
Although the majority of animal toxicity studies involved inhalation, SCCS also considered
data from studies with oral exposure to cyclomethicone: For D5 a LOEL of 100 mg/kg
bw/day was derived, based on liver weight increases reported in rat studies with gavage
administration for two and for 13 weeks. For D4 a LO(A)EL of 100 mg/kg bw/day was
derived, based on liver weight increases in mature rats after one week of dosing, and
decreased foetal body weights and liver to body weight ratios after administration of D4 to
pregnant rats.
Environmental aspects
The SCCS, in accordance with its mandate, has not considered possible environmental
effects resulting from the use of cyclomethicone containing cosmetic products or other uses
of D4 and D5.
Health Canada (2008), in recent reports covering this issue, concluded:
“Based on the available information on its potential to cause ecological harm, it is concluded
that D4 is entering the environment in a quantity or concentration or under conditions that
have or may have an immediate or long-term harmful effect on the environment or its
biological diversity.“
„Based on the available information on its potential to cause ecological harm, it is concluded
that D5 is entering the environment in a quantity or concentration or under conditions that
have or may have an immediate or long-term harmful effect on the environment or its
biological diversity.“
The Commission Services should consider whether an environmental risk assessment
associated with the use of cyclomethicone (D4/D5) in cosmetic products is required.

101

SCCS/1241/10
Opinion on cyclomethicone (D4 / D5)
___________________________________________________________________________________________

4. CONCLUSION
The SCCS is of the opinion that cyclomethicone (D4, D5) does not pose a risk for human
health when used in cosmetic products. Other uses were not considered in this risk
assessment.
This conclusion is based on the currently available in-use concentrations as cited in this
opinion.
It should be noted that D4 is classified as a reprotoxic substance, category 3 [ECB 2006].
The NOAEL for systemic toxicity (150 ppm) used for this risk assessment also covers
reprotoxic effects (NOAEL = 300 ppm).
The Commission Services should consider whether an environmental risk assessment
associated with the use of cyclomethicone (D4/D5) in cosmetic products is required.

5. MINORITY OPINION
Not applicable
6. REFERENCES
Burns-Naas LA, Mast RW, Meeks RG, Mann PC, Thevenaz P. (1998) Inhalation toxicology of
decamethylcyclopentasiloxane (D5) following a 3-month nose-only exposure in Fischer
344 rats. Toxicol Sci. 43(2): 230-240 ..
Burns-Naas LA, Meeks RG, Kolesar GB, Mast RW, Elwell MR, Hardisty JF, Thevenaz P (2002)
Inhalation toxicology of octamethylcylotetrasiloxane (D4) following a 3-month noseonly exposure in Fisher 344 rats. Int J Toxicol 21: 39-53
Cosmetic Ingredient Review (2009) Amended Final Report of the Cosmetic Ingredient
Review Expert Panel of the Safety Assessment of Cyclomethicone, Cyclotetrasiloxane,
Cyclopentasiloxane, Cyclohexasiloxane, and Cycloheptasiloxane. Dezember 8, 2009;
Dow Corning Corporation (1986). Summary of toxicology on cyclic and linear diemthylsiloxane oligomers and polymers. March 14, 1986 [cited in ICLID 2000, ref. 53]
Dow Corning Corporation (2004). 24-month combined chronic toxicity and oncogenicity
whole body vapor inhalation study of octamethylcyclotetrasiloxane (D4) in Fischer 344
rats. Report no. 2004-10000-54091
Dow Corning Corporation (2005). Decamethylcyclopentasiloxane (D5): A 24-month
combined chronic toxicity and carcinogenicity whole body vapor inhalation study in
Fischer 344 rats. Study No. 9346, Report no. 2003-10000-53252.
ECB 2006. European Chemicals Bureau. Summary Record. Commission Working Group of
Specialised Experts in the field of Reproductive Toxicity. ECBI/51/07. Ispra, 19-20
September 2006
Falany CN and Li G (2005) Effects of age and pregnancy on cytochrome P450 induction by
octamethyl-tetracyclosiloxane in female Sprague-Dawley rats. J Biochem Mol Toxicol.
19(2): 129-138
Horii Y, Kannan K (2008) Survey of organosilicone compounds, including cyclic and linear
siloxanes, in personal-care and household products. Arch Environ Contam Toxicol.
55(4): 701-710.
Jäger R and Hartmann E (1991) Subchronische toxikologische Untersuchungen an Ratten
(Magensondenapplikation über 13 Wochen). Bayer AG. Report no. 20204, May 3, 1991
Jovanovic ML, McMahon JM, McNett DA, Tobin JM, Plotzke KP (2008) In vitro and In vivo
102

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percutaneous absorption of 14C-octamethylcyclotetrasiloxane (14C-D4) and 14C-decamethylcyclopentasiloxane (14C-D5). Regul Toxicol Pharmacol 50: 239–248
Lassen C. Hansen CL, Mikkelson SJ, Maag J. Siloxanes - Consumption, Toxicity and
Alternatives. Danish Ministry of the Environment. Environmental Protection Agency.
Environmental Project No. 1031, 2005
Ministers of the Environment and of Health, Canada. Screening Assessment for
Octamethylcyclotetrasiloxane (D4). November 2008
Ministers of the Environment and of Health, Canada. Screening Assessment for
Decamethylcyclopentasiloxane (D5). November 2008
OEHHA (2007). Toxicity Data Review: Decamethylcyclopentasiloxane (D5). September 13,
2007. Available at: www.oehha.ca.gov/multimedia/biomon/pdf/1208cyclosiloxanes.pdf
Reddy MB, Looney RJ, Utell MJ, Plotzke KP, Andersen ME. (2007) Modeling of human dermal
absorption of octamethylcyclotetrasiloxane (D4) and decamethylcyclopentasiloxane
(D5). Toxicological Sciences 99(2): 422–431
Siddiqui WH, Stump DG, Plotzke KP, Holson JF, Meeks RG (2007a) A two-gene-ration
reproductive toxicity study of octamethylcyclotetrasiloxane (D4) in rats exposed by
whole-body vapor inhalation. Reprod Toxicol. 23(2):202-215
Siddiqui WH, Stump DG, Reynolds VL, Plotzke KP, Holson JF, Meeks RG. (2007b) A twogeneration reproductive toxicity study of decamethylcyclopentasiloxane (D5) in rats
exposed by whole-body vapor inhalation. Reprod Toxicol. 23(2):216-225.
Talberg H.J. Cyclic siloxanes D4 and D5 – in which concentration and with what frequency
are they used in cosmetic products? Norwegian Food Safety Authority. Note 2006-1119
Wang R, Moody RP, Koniecki D, Zhu J (2009) Low molecular weight cyclic volatile
methylsiloxanes in cosmetic products sold in Canada: implication for dermal exposure.
Environ Int. 35(6): 900-904.

103

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Keywords                        : SCCS, scientific opinion, hair dye, cyclomethicone, D4, D5, cyclotetrasiloxane, cyclopentasiloxane, directive 76/768/ECC, CAS
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Title                           : Opinion of the Scientific Committee on Consumer Safety on cyclomethicone (D4/D5)
Creator                         : muyldjn
Description                     : Scientific Committee on Consumer Safety
Author                          : muyldjn
Subject                         : Scientific Committee on Consumer Safety

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