Antioxidant: Any substance that reduces oxidative damage (damage due to oxygen) such as that caused by free radicals. Free radicals are highly reactive chemicals that attack molecules by capturing electrons and thus modifying chemical structures.

Well-known antioxidants include a number of enzymes and other substances such as vitamin C, vitamin E and beta carotene (which is converted to vitamin A) that are capable of counteracting the damaging effects of oxidation. Antioxidants are also commonly added to food products like vegetable oils and prepared foods to prevent or delay their deterioration from the action of air.

Antioxidants may possibly reduce the risks of cancer and age-related macular degeneration (AMD). Antioxidants clearly slow the progression of AMD.