Steareth-21

Steareth-21 is a nonionic ethoxylated fatty alcohol surfactant/emulsifier used to solubilize and stabilize formulas, typically around ~0.5–5%. While not a “strong active,” surfactants of this class can disrupt the stratum corneum barrier and sting on compromised skin, with irritation risk increasing in leave-on products and in eczema-prone patients. Given real-world cumulative exposure (cleansers + moisturizers) and higher reactivity in barrier-impaired populations, it fits a mild but non-negligible irritancy profile. Safety Notes: Steareth-21 is a nonionic emulsifier/solubilizer most often used at low levels (~0.1–1%) to stabilize O/W emulsions and improve texture in leave-on creams/lotions and some rinse-off cleansers. In high-oil-load or highly structured emulsions (including some OTC body butters, sunscreen-like emulsions, and conditioning creams), it can be pushed into the mid-single-digits as a primary emulsifier/co-emulsifier, with the upper end around ~6–8% observed in consumer-available products. There is no specific FDA/EU maximum concentration limit for Steareth-21 as used in cosmetics; practical limits are set by skin feel/irritation potential and formula stability rather than regulation.