Antioxidants are molecules which can safely interact with free radicals and terminate the chain reaction before vital molecules (like DNA) are damaged. They do this by donating an electron to the free radials so they have paired electrons and be more stable. Like with free radicals, antioxidants can be endogenous (e.g. superoxide dismutase, catalase, glutathione peroxidase, glutathione, coenzyme Q10) or exogenous (vitamins A, C and E, selenium, zinc, flavonoids, carotenoids, omega 3 fatty acids)