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In pathology, a carcinogen is any substance or agent that promotes cancer. Carcinogens are also often, but not necessarily, mutagens or teratogens.
Carcinogens cause cancer by altering DNA in cells, interfering with normal biological processes. Usually cells are able to detect this and attempt to repair the DNA; if they cannot, they undergo cell death to prevent further damage. When the damage interferes with cell death or encourages cell division, cancer occurs. Rapidly dividing cells, such as in skin, the stomach lining, breast tissue, and reproductive organs, are particularly sensitive to carcinogens due to harmful DNA being quickly copied.
Nearly all carcinogens consumed by humans are produced by plants to prevent animals from eating them. Plants containing large amounts of carcinogens include aristolochia and bracken. Aflatoxin B1, which is produced by the fungus Aspergillus flavus growing on improperly stored grains and nuts, is an example of a naturally-occurring carcinogen of considerable potency.
DDT, benzene, kepone, EDB, and asbestos have all been classified as carcinogenic. Tobacco smoke has also been identified as a rich source of dozens of carcinogens, including benzopyrene, tobacco-specific nitrosamines such as nitrosonornicotine, and reactive aldehydes such as formaldehyde. Certain viruses such as Hepatitis B and human papilloma viruses have also been found to cause cancer in humans.
CERCLA identifies all radionuclides as carcinogens, although the nature of the emitted radiation, its capacity to generate ionization in biological systems, and the magnitude of a given radiation exposure determine its potential to pose a meaningful carcinogenic hazard. For example, Thorotrast, a suspension that was previously used as a contrast medium in x-ray diagnostics, is thought by some to be the most potent human carcinogen known because of its absorption and slow re-distribution in various organs.
Recent reports have implicated acrylamide in fried or overheated carbohydrate foods (such as french fries and potato chips) as a potential carcinogenic hazard. Studies are currently underway at the US Food and Drug Administration and equivalent European regulatory agencies to assess the potential magnitude of the risk (if any) for cancer development from dietary acrylamide.
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