Carcinogens are substances that cause cancer. Sometimes radiation or radionuclide are also considered carcinogens. A common example of a carcinogen is tobacco smoke. Carcinogens come from both natural and man-made substances.[1]
↑Ames, Bruce N; Gold, Lois Swirsky (2000). "Paracelsus to parascience: The environmental cancer distraction". Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis. 447 (1): 3–13. doi:10.1016/S0027-5107(99)00194-3. PMID10686303.