Isostearic Acid
Well toleratedEmollientemollientemulsifierskin conditioning
No meaningful concern for most people; irritation is possible but rare.
Also written as: Isooctadecanoic acid
What it is
Isostearic acid is a branched-chain version of stearic acid. The branching stops the molecules packing neatly, so it remains a stable liquid rather than a wax and does not oxidise easily. Formulators use it for a light, spreadable emollient feel and to help disperse pigments and mineral powders.
What it does well
Light, oxidation-stable emollience
Its branched structure gives good spreading and a longer shelf life than unsaturated liquid fatty acids.
Moderate evidence
Where the EU stands
No specific restriction
No EU restriction on use or concentration in cosmetics.
