What it is
Steareth-3 is stearyl alcohol ethoxylated with about three units of ethylene oxide, giving a more lipophilic, lower-HLB surfactant than higher-numbered steareths. It is frequently paired with a more hydrophilic emulsifier such as steareth-21 to build robust oil-in-water emulsion systems. In sunscreens it helps create a stable, smooth-feeling base.
Safety & warnings
Steareth emulsifiers are generally well tolerated at the levels used in cosmetics. As an ethoxylated material it is manufactured under controls that limit residual 1,4-dioxane and ethylene oxide. It is not considered notably comedogenic at typical use levels.
Origin & sourcing
Synthetic; made by reacting stearyl alcohol (a fatty alcohol, often plant- or petrochemical-derived) with ethylene oxide.
Questions everyone asks
How does steareth-3 differ from steareth-10?
Steareth-3 has fewer ethylene oxide units, making it more oil-loving (lower HLB), so it is often combined with a higher steareth for balance.
What is its role in sunscreen?
It acts as a nonionic emulsifier that helps stabilize the oil and water phases of the formula.