Substances that slow the rate of oxidation reactions. Various antioxidants are used to preserve foodstuffs and to prevent the deterioration of rubber, synthetic plastics, and many other materials. Some antioxidants inhibit the oxidation reaction by removing oxygen free radicals. Naturally occurring antioxidants with this ability include vitamin E, β-carotene, glutathione, and superoxide dismutase; they limit the cell and tissue damage caused by superoxide radicals, hydrogen peroxide, hydroxide radicals, and other highly reactive substances.