Antioxidants are compounds that inhibit oxidation. Oxidation is a chemical reaction that can produce free radicals, thereby leading to chain reactions that may damage the cells of organisms. Antioxidants such as thiols or ascorbic acid terminate these chain reactions. Antioxidants are substances that can prevent or delay the damage to cells caused by free radicals and unstable molecules that the body produces as a reaction to environmental and other pressures. They are sometimes called “free-radical scavengers.” The sources of antioxidants can be natural or artificial.