Steartrimonium Methosulfate

Steartrimonium methosulfate is a quaternary ammonium compound—a type of cationic (positively charged) surfactant derived from stearyl alcohol. It functions as a conditioning and antistatic agent in personal care products.In cosmetic formulations, it deposits onto the hair or skin surface, where its positive charge attracts to negatively charged keratin fibres. This interaction reduces static electricity, improves combability, and imparts a smoother feel. It is commonly found in hair conditioners and detangling products rather than traditional skincare.

Steartrimonium methosulfate works through electrostatic attraction. The ingredient carries a positive charge, which binds to the negatively charged surface of hair keratin. This neutralises static electricity that would otherwise cause hair to repel itself and appear frizzy.The ingredient also forms a thin, lubricious film on the hair surface, which reduces friction between fibres during combing or styling, lowering the risk of breakage and improving slip and smoothness.

This ingredient is primarily used in rinse-off hair products such as conditioners and detangling sprays. If present in a leave-on skincare product, simply apply as directed. Avoid excessive product buildup by using only the amount needed; a little goes a long way with conditioning agents. Rinse thoroughly if using in a wash-off formula.

Steartrimonium methosulfate is generally well-tolerated and approved for use in cosmetics across major regulatory bodies. It is not a true sulphate (despite occasional confusion with sulphate-free marketing), though it is best avoided by those with known sensitivities to quaternary ammonium compounds.