Superoxide radicals are formed in a number of metabolic reactions, including lipid peroxidation initiated by light. One of the reasons why the superoxide radicals are so dangerous is because they start chain reactions where more and more free radicals are formed, wreaking havoc in the body. The main chain-breaking antioxidants are the water-soluble Superoxide Dismutase (SOD) and the lipid-soluble alpha-D-tocopherol (vitamin E). Lipid peroxidation occurs everywhere in the skin, not just in the live cells but also in the epidermis. The role of SOD is to eliminate the free radicals resulting from lipid peroxidation and to prevent the chain reactions that would eventually reach deeply into the skin.