Ethylene/acrylic acid copolymer is a synthetic copolymer of ethylene and acrylic acid monomers. Ethylene is the simplest alkene (a hydrocarbon with carbon-carbon double bonds), while acrylic acid is the simplest unsaturated carboxylic acid. Ethylene/acrylic acid copolymer functions as a binder and film-former in dyes, adhesives, and skin care products. The Cosmetic Ingredient Review (CIR) Expert Panel warns that ethylene/acrylic acid copolymer can be an irritant, therefore, it must be used with caution and under certain qualifications, including careful formulation to avoid irritation. Ethylene/acrylic acid copolymer can also be toxic when absorbed through the skin at high levels. Therefore, it is only a safe ingredient in skin care products when it is formulated to have a low absorption rate.