Silicones are a large group of compounds that include large polymers containing silicon. Depending on the formula and the degree of polymerization and cross-linking of the polymers, they may be slippery liquids, waxes, or rubbers.
Silicones are used as emollients (skin softeners), as lubricants, as thickeners, and as volatile liquids that make coatings feel smooth, but evaporate without leaving a greasy residue.
Highly cross-linked silicone films are used in cosmetics to form films that absorb sebum (skin oils) and prevent shine.
Cyclopentasiloxane is a low viscosity, volatile liquid used as a carrier. It lubricates, and prevents hair sprays from being sticky to the touch. It evaporates completely, leaving no residue.
Dimethicone is another name for polydimethylsiloxane and is used to impart a soft velvety feel to hair or skin products. It is also used as an emulsifier for "water-in-oil" emulsions.
Trimethylsiloxysilicate is a film forming resin, used to keep hand lotions and sunscreens from washing off.
Cetearyl methicone is a polysiloxane wax. It replaces petrolatum in products such as hand lotions to give them a non-greasy feel.
Silicone Use with Skin and Hair
Unmodified silicones stay on or near the surface of the skin. Not only are the molecules too big to physically enter past the upper living cells -- they associate with the upper layer of drying skin -- but they also cannot penetrate cell membranes due to their large size. They also dislike both the water and proteins inside cells.
Cyclomethicones are unmodified silicones. They evaporate quickly after helping to carry oils into the top layer of epidermis. From there, they may be absorbed by the skin. Cyclomethicones a similar function in hair care products by helping nutrients enter the hair shaft.
Dimethicones are also unmodified silicones. They form a barrier layer on the skin which must be renewed as the skin sloughs off. Dimethicones coat the surface of the hair and lubricate it, improving combing providing detangling, and thus, hair loss and breakage.
Silicones form a protective layer which helps prevent transdermal water loss -- a very useful characteristic for many products. Silicone gums provide instant shine to hair. Silicones act to help seal moisture into the hair, which helps prevent many kinds of damage.
Many formulas use 2 parts cyclomethicone to 1 part dimethicone. Silicone gums are generally not usable for lotions and other emulsified products. This is due to the insolubility of the gum in fixed oils . It is possible to make emulsions from silicone oils only, or with mineral oil. These types of emulsions allow for the incorporation of the gums into products such as hair dressings.
Cyclomethicone may be used alone to carry essential oils in a dry oil spray -- referred to commonly as "dry perfume oil sprays". It may also be used to dilute gums to produce spray detanglers. The gum base content in a hair serum spray is usually between 5 and 10%.