Classification of Common Silicones in Cosmetics
I. Characteristics of Silicones
Silicones have the characteristics of high temperature resistance and good stability. The affinity between molecules is weak, so the surface tension is extremely low. Silicones have good compatibility with other oils and fats. Silicones are highly inert. When applied on the skin, the skin feel is refreshing and the texture is light. It has low irritation to the skin. The skin hardly absorbs it, so there is no need to worry about it penetrating into the skin. It is relatively friendly to the environment. When it volatilizes into the atmosphere, it can decompose. No enrichment phenomenon is found in water. Because the surface tension of silicone is extremely low, it can quickly spread on the skin. Cosmetics prepared with it have a moist but not greasy skin feel.
II. Common types of silicones

1. Dimethyl silicone
   • Polydimethylsiloxane has various viscosities, generally including 0.6, 5, 10, 100, 350, 1000 and other viscosities. Low viscosity is suitable for adding to skin care products to provide a relatively refreshing moisturizing feeling. High viscosity is suitable for skin care products with strong moisturizing feeling. Ultra-high viscosity is suitable for adding to hair care products and scar removal products.
2. Polydimethylsiloxane alcohol
   • Generally, it is a solution of ultra-high viscosity polydimethylsiloxane alcohol mixed with low viscosity polydimethylsiloxane. It has an extremely lubricating skin feel. Polydimethylsiloxane alcohol can give the hair a soft and silky feeling. It uses anionic emulsification method, so it has an appropriate apparent viscosity and is extremely easy to add to shampoos and shower products and disperse evenly. It can also stabilize the product viscosity and keep the product consistent in spring, summer, autumn and winter. Due to the medium particle size of silicone oil, it can effectively improve the wet combing and dry combing performance of the product and improve the hair tangling phenomenon caused by dryness that often occurs in the shampoo product during rinsing and semi-rinsing.
3. Phenyl silicone
   • Phenyltrimethylsiloxane is a low-viscosity colorless and transparent liquid with slight volatility and high refractive index. It is extremely easy to compound with alcohols and organic components. It has good anti-stickiness and can also increase the solubility of silicone oil and other oils. Phenyl silicone can be used to brighten the gloss of the paste.
4. Polycyclic siloxane
   • Cyclopentasiloxane is a colorless, odorless, and non-irritating volatile liquid with good glossiness, water resistance, softness, and dryness. It is relatively easy to emulsify (low viscosity). Polycyclic dimethylsiloxane has an appropriate evaporation rate. Its evaporation rate is lower than that of water and ethanol. It has good dispersibility and volatility. When it volatilizes, the skin has no cold feeling and no residue. It is generally used in volatile refreshing creams and hair care essential oils.
5. Polyether modified silicone
   • This kind of silicone can be dissolved in water, ethanol, and emulsified systems. It is suitable for adding to skin lotions as an emollient and in leave-on hair care products as a softener.
6. Organic silicone emulsion
   • Generally added to shampoos as a softener. A suspending agent needs to be added to prevent silicone oil from precipitating. It has good dry combability.
7. Amino silicone
   • It provides good softness and damaged hair repair performance in hair care products. It is generally used in hair conditioners, hair masks, and hair treatment creams. Attention should be paid to the discoloration problem of some amino silicones.
8. Water-soluble silicone grease
   • Bis-PEG-18 methyl ether dimethylsilane has good water solubility and is generally used in aqueous agents as a fat-imparting emollient.
9. Silicone elastomer
   • Generally, it is cyclopentasiloxane, polydimethylsiloxane cross-linked polymer or polydimethylsiloxane, polydimethylsiloxane/vinyl polydimethylsiloxane cross-linked polymer. It has a powdery texture, can fill skin wrinkles and has a soft focus effect. It is generally used in high-end creams or emulsions to adjust the skin feel and in eye products.

III. Applications of silicones

1. Shampoo: Generally, emulsified silicone oil is used, with a combination of large and small particle sizes. In old formulations, high-viscosity polydimethylsiloxane is emulsified and then added. Attention should be paid to suspension.
2. Hair mask: Generally, amino silicone is used, which has a good effect on repairing hair.
3. Emulsified skin care products: In creams and lotions, medium and low viscosity polydimethylsiloxane and phenyl silicone are generally added to obtain a refreshing skin feel. Lubricating silicone oils such as polydimethylsiloxane alcohol are used to adjust the skin feel. For eye products or anti-wrinkle products, silicone elastomers are used to adjust the soft skin feel and matte anti-wrinkle effect.
4. Hair care essential oil: Generally, polycyclic siloxane is combined with polydimethylsiloxane to make a full-oil system hair care essential oil.
5. Essence oil: Generally, polycyclic siloxane is combined with silicone elastomer and polydimethylsiloxane alcohol to achieve the purpose of thickening and adjusting the skin feel.
6. Aqueous products: Generally, water-soluble silicone grease and polyether modified silicone are used to adjust the skin feel and moisture.