Carcinogens are chemical substances that modify the structure or expression of the DNA genome of cellss to initiate or promote the process of malignant transformation, or cancer. The term is commonly employed to refer to agents that have been introduced by human means, but is correctly used to refer to any substance that can cause cancer. 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 such as 3,4-benzpyrene (synonym: benzo(a)pyrene), tobacco-specific nitrosamines such as N-nitrosonornicotine and reactive aldehydes such as formaldehyde. Even traditional foods such as bracken (in Japan) and herbal medicines such as aristolochia are sometimes found to be carcinogenic. 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. CERCLA identifies all radionuclides as carcinogens, although the nature of the emitted radioactivity, 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 by some thought to be the most potent human carcinogen known, because of its absorption and slow re-distribution in various organs. Certain viruses such as Hepatitis B and human papilloma viruses have also been found to cause cancer in humans.
Recent reports have implicated Acrylamide in fried or heavily-heated 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.
Carcinogens are also often, but not necessarily, mutagens or teratogenss.
