Trihydroxystearin is a lipid composed of glycerin and hydroxystearic acid, a fatty acid that is structurally similar to stearic acid. Hydroxystearic acid can be produced through the hydrogenation and saponification of castor oil. Trihydroxystearin is used in creams, lipsticks, massage gels, balms, and other types of skin care and cosmetic products. It provides thixotropic thickening (shear thinning properties) in various oils including mineral, vegetable, and silicone oils. Thixotropic thickeners help to maintain a consistent viscosity, prevent settling, and improve product stability.
Trihydroxystearin can also be used as a binder in makeup products. As the name implies, a binder is an ingredient that binds together other ingredients. Therefore, as a binder, trihydroxystearin functions to prevent other ingredients used in a cosmetic formulation from coming apart. For example, binders are often used in pressed powders to keep them together in the container. Lastly, trihydroxystearin functions as an occlusive emollient. After application, it forms a thin film on the skin that helps to prevent evaporation of the skin’s natural moisture. Over time, this increases skin hydration by causing buildup of water in the stratum corneum (the uppermost layer of skin).