What it is
Sodium stearate is a classic soap formed from stearic acid and sodium hydroxide. It can gel and harden oil or solvent phases, which makes it a common structuring ingredient in sunscreen sticks and other solid or semi-solid formats, and it also serves as an emulsifier and thickener. Its film-forming, structuring behavior helps give stick products their firm yet glideable feel.
Safety & warnings
Generally well tolerated and widely used; as an alkaline soap it can be mildly irritating to very sensitive or compromised skin. It is considered low on the comedogenicity scale and is not a known fragrance allergen.
Origin & sourcing
Made by neutralizing stearic acid, a fatty acid that can be sourced from plant or animal fats, with sodium hydroxide.
Questions everyone asks
Why is sodium stearate used in sunscreen sticks?
It gels and hardens the base, giving stick formats their solid structure while still allowing them to glide and deposit on skin.
Is sodium stearate a soap?
Yes. It is the sodium salt of stearic acid, the same chemistry as traditional bar soap, used here as a structuring and emulsifying agent.