The use of antioxidants in cosmetics has a long history. Two different modes of application can be distinguished. They are used either to stability the cosmetic formulation or to protect the skin.
As a formulation stabilizer, they serve as a "technical antioxidant." Here they are being used to prevent the oxidative deterioration of labile ingredietns such as unsaturated fatty acids or oxidation-prone active ingredeitns. Both synthetic compounds like butylated hydroxytoluene and natural antioxidants like alpha-tocopherol are frequently used for this purpose.