What it is
Stearic acid is a saturated fatty acid with an 18-carbon chain (IUPAC name octadecanoic acid, formula CH3(CH2)16COOH) that is a soft, waxy solid at room temperature. As a multitasking fatty acid it acts as an emollient that leaves skin feeling smooth and as a viscosity-controlling agent that gives body to creams and helps stabilize oil-and-water emulsions. When partly neutralized with an alkali it also forms soap-like surfactants, which is why it turns up in cleansers and shaving products as well as in moisturizers and sunscreens.
Safety & warnings
Stearic acid is a fatty acid the skin and many foods already contain and has a long record of safe cosmetic use, with a very low expected irritation potential, which is why it is common even in products for sensitive skin. Because it is an oil-phase fatty material, it carries a low-to-moderate pore-clogging tendency that matters mainly to people very prone to congestion in rich, leave-on formulas. Most people tolerate it well.
Origin & sourcing
Stearic acid is found in both animal and vegetable fats, with especially high levels in beef tallow, lard, and butterfat, plus notable amounts in cocoa butter and shea butter. Commercially it is obtained by saponifying or hydrolyzing fats and oils and then distilling the fatty acids, and oleic acid from sources such as palm and soy can also be hydrogenated to yield it.
History
Stearic acid was first isolated and named by the French chemist Michel Eugene Chevreul, who in his 1823 memoir on animal fats resolved fats into a solid principle (stearin) and a liquid one (olein) and isolated stearic and oleic acids, coining their names. His work, including a candle-making patent with Gay-Lussac, founded the modern chemistry of fats. The name comes from the Greek stear, meaning tallow.
Questions everyone asks
What is stearic acid used for in skincare?
It thickens and stabilizes creams and lotions and acts as an emollient, and when neutralized it helps form mild cleansing surfactants.
Is stearic acid animal or plant derived?
It can be either; it occurs in animal fats like tallow and in plant fats like cocoa butter and shea, and is also made by hydrogenating plant-derived oleic acid.
Does stearic acid clog pores?
It has a low-to-moderate pore-clogging tendency, which is mostly a concern for very congestion-prone skin in rich leave-on products.