Antioxidants serve to protect against certain particles called free radicals. In dogs, free radicals usually come in the form of O2, the oxygen molecule. Free radicals are the natural by-products of many processes within and among cells. They are also created by exposure to various environmental factors, pollution, for instance. If allowed to go about their business, these free radicals can lead to health problems. Antioxidants play the housekeeper's role, "sponging up" free radicals before they get a chance to do harm.