Silicones have become integral to many cosmetic and personal care products because they reduce surface tension, emulsify, disperse pigments, and generate foaming action. They also contribute a light and silky feel that enhances a product’s sensory experience. Cyclomethicone refers to a family of silicones — the cyclic dimethyl polysiloxane compounds. Cyclomethicone is a group of methyl siloxanes, a class of liquid silicones (cyclic polydimethylsiloxane polymers) that possess the characteristics of low viscosity and high volatility as well as being skin emollients and, in certain circumstances, useful cleaning solvents.
What is Cyclomethicone?
Cyclomethicone is a general term for cyclic dimethyl siloxanes and may indicate individual or combined cyclic siloxane materials. According to INCI, it includes cyclotetrasiloxane (D4), cyclotrisiloxane (D3), cyclopentasiloxane (D5), cyclohexasiloxane (D6), and cycloheptasiloxane (D7). The nomenclature is based on the number of siloxane groups in the cyclic structure. For example, cyclopentasiloxane has five groups, cyclotetrasiloxane has four, etc.
All cyclomethicones are based on a common structure: a cyclic backbone of siloxane units (i.e., silicon and oxygen with carbon and hydrogen molecules attached). Unlike dimethicones, which are linear siloxanes that do not evaporate, cyclomethicones are cyclic and volatile. Both groups have a backbone of [(CH3)2SiO]n.
The most commonly used cyclomethicones are cyclotetrasiloxane (D4) and cyclopentasiloxane (D5).
Chemical structure of Cyclotetrasiloxane (top) and Cyclopentasiloxane (bottom). Sources: Wikipedia & Wikipedia
Use of Cyclomethicone in Cosmetics and Personal Care
Cyclomethicone is a clear, odorless silicone that evaporates quickly when applied to the skin, leaving a silky-smooth feel. Cyclomethicone compounds are typically used to provide “slip” and as a solvent to emulsify compounds in cosmetics, antiperspirants, serums, and sun care products. They’re also used in hair care products because they have an anti-static effect and fill porosity, making the hair smooth and shiny.
Applications in the Cosmetics Industry
| Function | Applications |
| Emollient | Cyclomethicone serves as a non-comedogenic emollient for skin care formulations. |
| Color Protection | Cyclomethicone can help colored hair retain its vibrancy longer and enhance color and shine. |
| Heat Protectant | Cyclomethicone is thermally stable and spreads easily on hair. It forms a protective film to help prevent water loss and damage caused by the heat of dryers or heat-styling tools. |
| Carrier | Cyclomethicone serves as a carrier in many skin care and hair care formulations. It also acts as a transient carrier for active salts in antiperspirants and deodorants. |
| Hair Conditioning | With their unique chemical and physical properties, Cyclomethicone conditions hair and adds shine, tames frizz, and makes combing easier. |
Product Examples
| Type | Examples |
| Bath & Shower Products | Bath Oils, Foaming Shower Gels |
| Hair Products | Hair Sprays, Hair Gels, Hair Styling Aids, Shampoos, Conditioners |
| Skin Care | Cleansing Creams, Skin Creams, Lotions, Stick Products, Body Lotions, Body Oils, Shaving Products |
| Antiperspirants/Deodorants | Antiperspirants, Deodorants |
| Color Cosmetics | Foundation, Mascara, Nail Polish, Primer, Lipsticks |
| Sun Care Products | Suntan Creams, Sunscreens, Sunblocks, Sunless Tanning Lotion |
Properties of Cyclomethicone:
| Cyclotetrasiloxane (D4) | Cyclopentasiloxane (D5) | |
|---|---|---|
| Chemical Name | Octamethylcyclotetrasiloxane | Decamethylcyclopentasiloxane |
| Chemical Formula | [(CH3)2SiO]4 | [(CH3)2SiO]5 |
| Appearance at 25°C | Clear, colorless Liquid | Colorless liquid |
| Viscosity (cSt) | 2.5 | 3.50 – 4.50 |
| Molecular Weight (g/ml) | 297 | 371 |
| Specific Gravity (at 25°C/15.6°C) | 0.95 | 0.950 – 0.960 |
| Density at 18°C (g/cm3) | 0.956 | 0.96 |
| Solubility in Water at 25°C | 20µg/L | 17-20 µg/L |
| Melting Point at 760 mmHg (°C) | 17–18°C | −47°C |
| Boiling Point (at 760 mmHg) | 175–176°C | 211°C |
| Flash Point (°C) | 76 | 77 |
| Refractive Index | 1.394 | 1.397 |
| Heat of Vaporization (at 25°C) kJ/kg | 172 kJ/kg | 157 kJ/kg |
| Odor | Odorless | Odorless |
| Shelf Life | 12-18 months | 12-18 months |
Recommended Storage and Handling
- Cyclomethicone should be stored at or below 5°C (9°F) in original, unopened containers.
- Care should be taken when handling volatile fluids at temperatures 10°C below the flash point.
- As with any flammable material, containers should be kept tightly closed and away from heat, sparks, open flames, and other ignition sources.
Typical Cyclomethicone Formulations
CC Cream
Here is an example of a CC (color control or color correcting) cream product formulation, along with percent weight of ingredients.
| PHASE | INCI Name | Trade Name | % Wt. |
| A | Deionized Water | Q.s to 100 | |
| Glycerin | 5.00 | ||
| Magnesium Stearate | 2.00 | ||
| Disodium EDTA | 0.05 | ||
| Preservative | 0.5 | ||
| B1 | Polyglyceryl-2 Oleate (and) Polyhydroxystearic Acid (and) Polyglyceryl-2 Stearate | PolyAquol™ OS2 | 6.00 |
| Isodecyl Neopentanoate | 6.00 | ||
| Paraffinum Liquidum | 4.00 | ||
| Octyldodecyl Oleate (and) Octyldodecyl Stearoyl Stearate (and)Polyhydroxystearic Acid (and) Octyldodecanol | Innollient™ LO | 3.00 | |
| Magnesium Stearate | 2.00 | ||
| B2 | CI 77891 (and) Triethoxycaprylylsilane | 1.77 | |
| CI 77492 (and) Triethoxycaprylylsilane | 0.13 | ||
| CI 77491 (and) Triethoxycaprylylsilane | 0.05 | ||
| CI 77499 (and) Triethoxycaprylylsilane | 0.05 | ||
| C | Cyclomethicone | 10.00 | |
| D | Ribes Nigrum (Black Currant) Seed Oil (and) Octyldodecanol (and) Octyldodecyl Oleate (and) Octyldodecyl Stearoyl Stearate (and) Paeonia Suffruticosa Root Extract (and) Rosmarinus Officinalis (Rosemary) Leaf Extract | Activoil™ Spotless ZRO | 0.50 |
| E | Parfum | q.s | |
| Total | 100% | ||
Cyclomethicone Formulation Procedure
- Prepare phase B1 and warm it up to 75°C.
- Crush phase B2 at the mill and add it to phase B1.
- Add phases C and D to phase B below 45-50°C.
- Prepare phase A and warm it up to 50°C.
- Add phase A to phase B+C+D under agitation and homogenize for a few minutes.
- Cool to 40°C and add phase E under gentle stirring.
Product Properties: VISCOSITY after 24h Brk, RVDV-I Prime, Sp 92, 10 rpm 15000 –20000 cps
Source: Knowde
Cyclomethicone Formulation Considerations
| Cyclotetrasiloxane (D4) | Cyclopentasiloxane (D5) | |
|---|---|---|
| Recommended Usage Level | 1-5% (Hair Care)0.5-3% (Perfumes)3-10% (Antiperspirants, Deodorants)2-10% (Skin Care) | 1-5% (Hair Care)0.5-3% (Perfumes)3-10% (Antiperspirants, Deodorants)2-10% (Skin Care) |
| Compatible with | Compatible with waxes like beeswax, paraffin waxHydrocarbons like petrolatumEsters and other silicones | Compatible with waxes like beeswax, paraffin waxHydrocarbons like petrolatumEsters and other silicones |
| Incompatible with | Castor oil, Glycerin, Water | Castor oil. It must be used with other surfactants to make it soluble in water-based formulations. |
Safety & Regulatory Considerations
| Regulatory | Cyclotetrasiloxane (D4) | Cyclopentasiloxane (D5) |
| FDA Information | The US Food and Drug Administration has approved the safety of cyclotetrasiloxane (D4). | The US Food and Drug Administration has approved the safety of cyclopentasiloxane (D5). |
| EU Information | Cyclotetrasiloxane (D4) is classified as a Category 1 endocrine disruptor by the European Commission. The European Chemicals Agency characterized D4 as persistent, bioaccumulative, and toxic. It has designated D4 as a Substance of Very High Concern. | As per EU guidelines, cyclopentasiloxane is safe to use for leave-on and rise-off applications. However, because it accumulates in the environment, D5 has been limited to less than 0.1% concentrations in wash-off cosmetics. |
| Cosmetic Ingredient Review (CIR) Information | The Cosmetic Ingredient Review Expert Panel concluded that cyclotetrasiloxane is safe in the present practices of use and concentration. | As per EU guidelines, cyclopentasiloxane is safe for leave-on and rise-off applications. However, because it accumulates in the environment, D5 has been limited to less than 0.1% concentrations in wash-off cosmetics. |
Safety & Toxicity of Cyclomethicone
- Skin/eye irritation and sensitization: According to OECD guidelines, a GLP study demonstrated that D4 is not a skin sensitizer. Tests on D5 provided no evidence that it is irritating the skin, mucous membranes, or a skin sensitizer.
- The SCCS is of the opinion that Cyclomethicone (D4, D5) does not pose a risk to human health when used in cosmetic products. Other uses were not considered in this risk assessment. While assessing D5’s safety, the SCCS concluded that the overall aggregate exposure to D4 was less than 5 µg/kg bw/day, which provides a margin of safety of > 3500.
- A 2018 study commissioned by the Danish EPA identified Cyclomethicone (D4) as an endocrine disruptor. In animals, it can affect the reproductive system. The Global Harmonized System Label Requirements classified D4 as suspected to produce reproductive toxicity. D4 was added to the Toxic Substances Control Act work plan due to reproductive toxicity, moderate environmental persistence, and high bioaccumulation potential. Adverse reproductive effects, including estrogenic effects, have been observed in rodents.
Identification Numbers
| Cyclotetrasiloxane (D4) | Cyclopentasiloxane (D5) | |
| CAS Number | 556-67-2 | 541-02-6 |
| EC Number | 209-136-7 | 208-764-9 |
Environmental Impact of Cyclomethicone
- While cyclopentasiloxane is generally safe for humans, it may harm the environment.
- Like other silicones, cyclopentasiloxane is a stable and nonreactive chemical that can take years to decompose. It may evaporate into the air or enter rivers and seas through drainage systems when someone rinses it off their skin or hair.
- In 2018, the European Union limited cyclopentasiloxane (D5) concentrations in rinse-off products to up to 0.1%.
Additional Resources
- Antistatic Agent – ScienceDirect
- Opinion on Cyclopentasiloxane (D5) in cosmetic products
- The Beauty of Silicone in Hair Care Application
- Cyclopentasiloxane – The Good Scents Company
- Silicone oils – Kremer Pigmente
- Cyclopentasiloxane in Personal Care Products
- Cyclopentasiloxane: Uses, Safety, and More
- Cyclopentasiloxane: What You Should Know
- Polysilicone-11: A new elastomer for personal care
- Polysilicone-11 – Cosmetic Ingredient Review
- Selecting the Perfect Silicone for Your Formulation
- Siloxane – Wikipedia
