Stearic Acid

Also known as Octadecanoic acid, n-Octadecanoic acid, Stearophanic acid, C18:0 fatty acid

Stearic Acid (octadecanoic acid; CAS 57-11-4; C18H36O2) is a C18 saturated fatty acid — one of the most abundant saturated fatty acids in animal and vegetable fats, and a primary component of cocoa butter, shea butter, and palm oil. In cosmetic formulations it functions as an emulsion stabilizer, pH adjuster (via saponification with alkaline ingredients to form in-situ stearate soaps), emollient, and opacifier. Stearic acid is particularly important in 'self-emulsifying' cream bases where it is neutralized with sodium hydroxide or triethanolamine to form sodium stearate or TEA-stearate, which then acts as the primary surfactant for oil-in-water emulsification. The Cosmetic Ingredient Review Expert Panel originally assessed Stearic Acid together with Oleic, Lauric, Palmitic, and Myristic Acid in 1987 (J Am Coll Toxicol 6(3):321-401) and concluded all five fatty acids are safe as used in cosmetics. The 1987 conclusion was reaffirmed in June 2005 (republished Int J Toxicol 25(Suppl 2), 2006). The Panel noted that Stearic Acid was reported to be used at up to 37.4% in rinse-off products (bath soaps and detergents) and up to 21% in leave-on products (eyebrow pencil). Clinical repeated insult patch tests, maximization tests, and prophetic patch tests with cosmetic formulations containing Stearic Acid at concentrations ranging from less than 1% to 13% showed no primary or cumulative irritation or sensitization. Acute and chronic toxicity studies demonstrated negligible adverse effects. Stearic Acid is FDA Generally Recognized As Safe (GRAS) as a direct and indirect food substance and is a natural component of many edible fats. The QRT row carries no conditions or concentration limits.