Why are Silicones Used in Hair Products?
Many currently available shampoos include silicones in the ingredient list. These additives act as conditioning agents, due to their ability to deposit onto the surface of the hair and form a film during the rinsing phase of the shampooing process.* This helps moisturize the hair by replacing oils stripped from the hair by the cleansing agents in the shampoo. Initially these were marketed as two-in-one products, but now they are found in a wide variety of products, especially as new properties are discovered, such as the ability of some silicones to enhance hair color retention. The inclusion of other oils in a shampoo can have a similarly moisturizing effect.
One interesting thing to note is that a published study in the Journal of Cosmetic science reports finding that the presence of cationic polymer (polyquaternium-10, in this study) significantly decreased the buildup of dimethicone on the hair over time.** The presence of these cationic polymers also enhances the deposition of the silicone onto the surface of the hair. Due to this synergy between the two types of ingredients, they will often be used together by formulators in shampoos.
Silicones offer many benefits, both to the hair care product formulator and the end-user. Careful reading of labels and understanding which silicones require occasional removal with surfactant-containing shampoos can allow the consumer to enjoy all of the good effects of silicones (softness, shine, better color retention, increased manageability), while suffering none of the ill effects of build-up.
* Marchioretto, S., "Optimizing the Use of Silicones in Haircare Products”, Dow Corning Europe, 1998
** Gruber JV; Lamoureux BR; Joshi N; Moral L, J.Cosmetic Sci; 2004, 52 (2), 131-136, "The use of x-ray fluorescent spectroscopy to study the influence of cationic polymers on silicone oil deposition from shampoo"