Silicone compounds are very versatile. There are two common types of silicones used in cosmetic products. The ring-like circular structures and straight or branched chains of silicones both have very different properties. Cyclic (circular) silicones (ie, cylcomethicones) evaporate quickly. This makes them suitable as carrier silicones as well as light degreasers for lotion or other emulsified products. Common applications include dry oil sprays, hair conditioners, and lotions. The use rates vary widely depending upon the application. Straight chain (dimethicones) silicones have a wide variety of properties based upon the length of the chain. Relative chain length is often differentiated by viscosity. The ultra-light ones are often blended with cyclomethicones for very quick soak-in.
The medium weight oils are commonly used to improve the feel of lotion products and can act as skin protectants. Silicones are often modified for a variety of reasons, including improving water dispersion and "consumer feel." Silicone compounds are usually recommended for external use only. Silicones come in several grades depending upon the use. Choosing the correct grade is important to ensure safety of your customer.
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 evaporae quickly after helping carry oils into the top layer of the skin. In hair products, cyclomethicone helps 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.
Silicones have varying properties which affects how they are used. Their solubility in a variety of ingredients is a most important consideration. Silicones usually blend readily with each other to provide desired properties. The solubility of silicones in other ingredients varies and must be observed when formulating.
Unmodified silicones are insoluble in water and other polar compounds. They will emulsify well, though, using the more common emulsifying agents. All-silicone emulsions are possible. Silicones can be modified or changed to improve water solublity. Silicone oils dissolve well in and will dissolve non-polar materials. These include essential oils, mineral oil, fixed oils, light esters, and sunscreen agents. Solubility decreases, however, as the size and viscosity of the silicone increases. Silicone oils are somewhat soluble in waxes, lanolin, castor oil and similar materials. The viscosity limitation is higher in these materials than it is for the fixed oils.
Usage rates of silicone compounds varies, however, is generally quite low. Their usual applications include lotions, salves, conditioners and bath products that use 1 to 5 % silicone as an additive to modify "feel" and provide skin protection. Cyclomethicones are most commonly used, with the low- to medium- viscosity dimethicones. Different types of silicone may be used alone or together. Many formulas use 2 parts cyclomethicone to 1 part dimethicone. Cyclomethicone may be used alone to carry essential oils in a dry oil spray -- referred to commonly as "dry perfume oil sprays".