A Co-carcinogen is a a chemical that promotes the effects of a carcinogen in the production of cancer. Usually, the term is used to refer to chemicals that are not carcinogenic on their own. A chemical can be co-carcinogenic with other chemicals or with nonchemical carcinogens, such as UV radiation. For example, sodium arsenite can be administered to mice at a low enough concentration that it doesn't cause tumors on its own, but it increases the rate of formation and size of tumors formed after… (More on Co-carcinogen)