Excessive physical or mental stress, cigarette smoke, radiation UV, radiation or radio therapy, air pollutants like car exhaust, ozone or smog, chemicals and medications in addition on our body with harmful radicals and peroxides. "Antioxidants" are a collective term for all those organic molecules, which are able to catch the biological spark of our metabolism (so the radicals and peroxides). They do this by them, similar to small fire extinguishers, the spark with organic foam (in this case electrons) bombard and thus harmless. These antioxidants are for example vitamin C, vitamin E, beta carotene, bioflavonoids, and much more.