Antioxidant” — an enzyme or other organic molecule that can counteract the damaging effects of oxygen in tissues. Although the term technically applies to molecules reacting with oxygen, it is often applied to molecules that protect from any free radical (molecule with an unpaired electron). The term antioxidant is used to describe a dietary component that can function to decrease the tissue content of reactive oxygen. Common antioxidants include vitamins C and E, beta-carotene, N-acetylcysteine, selenium, zinc and alpha-lipoic acid.