Cyclohexasiloxane is a type of silicone that is used in cosmetics and personal care products as a solvent, carrier fluid, skin conditioning agent, and emollient.
Cyclohexasiloxane is a type of silicone. Silicones are synthetic polymers with a backbone composed of repeating units of siloxane (elemental silicon and oxygen), which is why silicones may also be referred to as polysiloxanes. Often, the terms “silicone” and “silicon” are mistakenly used interchangeably, when they are actually quite different. Silicon is the 14th element on the periodic table and the second most abundant element in the earth’s crust, after oxygen. In contrast, silicones are always synthetically produced.
Cyclohexasiloxane can be further classified under the name cyclomethicone, which is the INCI (International Nomenclature for Cosmetic Ingredients) name for a category of cyclic silicones. In contrast with linear silicones, these molecules have a cyclic, or ring-like structure, comprised of only four to six repeat units of the dialkyl siloxane group. Cyclohexasiloxane is made up of six dialkyl siloxane groups, which is indicated by the “hexa” in the ingredient name. The group of cyclomethicone silicones are much smaller molecules than the polymeric silicones, such as polydimethylsiloxane (dimethicone), which may have hundreds of thousands of siloxane repeat units.
As a class, silicones improve the feel, appearance, and performance of cosmetic products. These ingredients act as silky moisturizers, conditioners, solvents, and delivery agents for other skin care ingredients. Silicones are able to help with skin redness and irritation due to their low surface tension, which enables them to spread easily across the surface of skin and form a protective covering.
Specifically, cyclohexasiloxane functions as a solvent for fragrance and essential oils, as well as a carrier fluid for higher molecular weight silicones such as dimethicone. This allows the formulator to prepare the oil phase of a cosmetic product by combining cyclohexasiloxane and the silicone and/or fragrance oil and add the emulsifier before adding the entire oil phase to the aqueous (water) phase. Overall, this improves the consistency of the final product.
Cyclohexasiloxane also functions as an emollient and skin/hair conditioning agent. Its fluidity allows it to spread easily on the skin and hair, forming a soft, invisible film. The film creates a lubricating, smooth, silky feel that does not feel greasy or sticky. It still allows oxygen, nitrogen, and other important nutrients to pass through, but blocks water from evaporating. Ultimately, this leads to skin that looks and feels hydrated and smooth. Additionally, the film formed by cyclohexasiloxane has mild water-repellency, which can be useful in the formulation of sun protection products.
Cyclohexasiloxane has a low vapor pressure, which means that is will evaporate easily from the skin or hair at room temperature. Due to this property, cyclohexasiloxane is not prone to build-up or an oily residue. The low vapor pressure of cyclohexasiloxane also enhances the delivery of active ingredients. While the structure of cyclohexasiloxane is too large to penetrate the skin or hair itself, it is small enough to dissolve the active ingredients and deposit these ingredients on the surface of skin or hair. Cyclohexasiloxane will then evaporate, leaving behind the active ingredients.
The safety of the group of cyclomethicone ingredients (including cyclohexasiloxane) has been assessed by the Cosmetic Ingredient Review (CIR) Expert Panel. The Panel noted that minimal percutaneous absorption was associated with these ingredients and the available data did not suggest skin irritation or sensitization potential. The Panel concluded that these ingredients are safe in the present practices of use and concentration.
Even though cyclohexasiloxane and other silicones have been proven both safe and effective for cosmetic purposes, there are claims that these ingredients are unsafe for topical use. However, since silicones are too large to penetrate the skin, they cannot cause allergic reactions or worsen skin conditions. Another claim is that the film formed by silicones somehow “suffocates” the skin. This claim is also false since the film still allows oxygen and other gases to pass through. Thus, the skin can still “breathe” after topical application of a product containing silicones.
References: NaturallyCurly.com “Cyclomethicones: A Different Category of Silicones” 2007, Int J Toxicol 2011 Dec;30(6 Suppl):149S-227S