Antioxidants "neutralize " free radicals, keeping them from getting out of control. Free radicals are constantly generated within the body as a result of normal metabolic processes; their actions kill harmful organisms and even destroy our body's own damaged cells, thus preventing cancerous growth. An over abundance of free radicals damage cells and their DNA; that is when the antioxidants come in and fix the problem.
Fruits and vegetables make antioxidants for their own protection from ultra violet radiations and oxidants. When we eat fruit and vegetables we get and use them for our own protection. The darker fruits and vegetables are, the greater the amount of antioxidants.
An example of antioxidant is lycopene found in tomatoes. Raw tomatoes are a source of vitamin C, cooked tomatoes of lycopene.
Supplements of antioxidants, such as lycopene pills, do not seem to be very effective.