Octadecene/MA copolymer is a substance used in cosmetic formulations. "Copolymer" means a polymer composed of several different (usually two) basic units (monomers). MA stands for "Maleic anhydride = maleic anhydride". The substance acts as a viscosity regulator (increases or decreases the viscosity of cosmetic products) and stabilizer (stabilizes the resistance and shelf life of ingredients or formulations).