Antioxidants are compounds that inhibit oxidation. Oxidation may be a reaction that will produce free radicals, thereby resulting in chain reactions that will damage the cells of organisms. Antioxidants like thiols or vitamin C (vitamin C) terminate these chain reactions. To balance the oxidative stress, plants and animals maintain complex systems of overlapping antioxidants, like glutathione and enzymes (e.g., catalase and superoxide dismutase), produced internally, or the dietary antioxidants vitamin C and vitamin E. The term "antioxidant" is usually used for 2 entirely different groups of substances: industrial chemicals that are added to products to stop oxidation, and present compounds that are present in foods and tissue. The former, industrial antioxidants, have diverse uses: acting as preservatives in food and cosmetics, and being oxidation-inhibitors in fuels.