Hydroxypropyl Dimethicone Stearate is an inorganic chemical compound, a Dimethicone by-product.

Safety
Dimethicone ((polydimethylsiloxane) is a chemical compound, a high molecular weight polymer derived from silicone, a chemically inert mixture of linear methylated siloxane polymers. The term 'dimeth' denotes two methyl groups bonded to the silicone molecule that provide the formation of dimethicone. It possesses a pronounced viscoelasticity characteristic and is hydrophobic, thus adding shine and slipperiness when applied to hair or skin. It forms a kind of barrier that prevents exogenous substances from entering the stratum corneum and at the same time prevents water loss. It is also UV-resistant, non-greasy and cost-effective. At low concentrations it is considered by the US FDA (Food and Drug Administration) to be a skin protector with a good degree of safety.
It is therefore considered safe when formulated to be non-irritating in cosmetic products as, given its high molecular weight, it is poorly absorbed by the skin or scalp.

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What it is used for and where
Cosmetics
Skin conditioning agent - Emollient. Emollients have the characteristic of enhancing the skin barrier through a source of exogenous lipids that adhere to the skin, improving barrier properties by filling gaps in intercorneocyte clusters to improve hydration while protecting against inflammation. In practice, they have the ability to create a barrier that prevents transepidermal water loss. Emollients are described as degreasing or refreshing additives that improve the lipid content of the upper layers of the skin by preventing degreasing and drying of the skin. The problem with emollients is that many have a strong lipophilic character and are identified as occlusive ingredients; they are oily and fatty materials that remain on the skin surface and reduce transepidermal water loss. In cosmetics, emollients and moisturisers are often considered synonymous with humectants and occlusives.
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