A carcinogen is any substance, radionuclide, or radiation that promotes carcinogenesis, the formation of cancer. This may be due to the ability to damage the genome or to the disruption of cellular metabolic
processes. Several radioactive substances are considered carcinogens,
but their carcinogenic activity is attributed to the radiation, for
example gamma rays and alpha particles, which they emit. Common examples of non-radioactive carcinogens are inhaled asbestos, certain dioxins, and tobacco
smoke. Although the public generally associates carcinogenicity with
synthetic chemicals, it is equally likely to arise in both natural and
synthetic substances.[1] Carcinogens are not necessarily immediately toxic; thus, their effect can be insidious.