A carcinogen is anything that induces
cancer. Carcinogens are usually thought of as
chemical in nature, like
benzene or
tobacco smoke, but may also cause cancer through physical action, as with
ultraviolet light or
asbestos. Carcinogens do not tend to fall into deeper categories -- just as there are hundreds of kinds of
cancer, there are hundreds (or thousands, or more) of
vectors that may cause it to start.
Determining what agents are and are not carcinogenic is done by committee, through sort of an ad-hoc voting system. Two committees are responsible for this determination: internationally, the International Agency for Research on Cancer (IARC), part of the World Health Organisation; and in the US, the Annual Report on Carcinogens done by the National Toxicology Program (NTP).
The IARC format is more widely used, and divides carcinogens into three categories. Category 1 carcinogens are those which have a determined relationship with cancer in humans; confirmed human carcinogens. Category 2A includes agents which have less evidence in humans, but are unequivocally confirmed carcinogens in animal studies; probable human carcinogens. Category 2B is for substances which have some evidence from animal experimentation, and are considered good candidates for further study; possible human carcinogens. Finally, there is Category 3, which I don't know much about except that their evidence for acceptance is considered "limited."
The NTP format is easier, with only two categories. These definitions are both copied directly from the NTP report. A, profiles for agents, substances, mixtures or exposure circumstances known to be human carcinogens. And B, profiles for agents, substances, mixtures or exposure circumstances reasonably anticipated to be human carcinogens. While the NTP report and format are less accepted by the world, it should be noted that the NTP leads the world in experimentation to determine toxicity and carcinogenicity.
Here are some of the more interesting and unexpected carcinogens from the lists:
- Alcoholic Beverages - that's right kids, booze causes cancer of the mouth, pharynx, esophagus, larynx, colon, rectum, liver, and possibly breast.
- Asbestos - and other "asbestiform" particles, to a lesser degree. These include fiberglass and talc.
- Benzene - fairly common. Be careful.
- Carbon Tetrachloride - that's why we don't dry-clean with it any more.
- Carpentry / Wood Industry - caused by the curing agents used on wood.
- Chloroform - one more reason not to try and knock people out with it.
- Conjugated Estrogens - and steroidal estrogen, like birth control and what post-menopausal women take. Causes endometrial and breast cancer.
- Dietary Fat / Obesity - apparently causes cancer of the breast, prostate, colon, rectum, and endometrium.
- Human Papillomavirus - found in 90% of all cervical cancers.
- Lead and Lead Compounds - also notable for nasty heavy metal poisoning.
- Mate - an herbal drink commonly used in Argentina, Bolivia, Brazil, Chile, Ecuador, Paraguay and Uruguay.
- Mustard Gas - ok, maybe you don't need to worry about this one.
- Phenobarbitol - sad news for junkies everywhere.
- Petroleum Industry - lots and lots of biohazards in the air.
- Radon - it's possibly in your basement, and is responsible for many of the so-called "black lung" cancers that miners get.
- Salt / Cured Foods - besides the blood pressure issue, causes stomach cancer.
- Safrole - don't take nutmeg to trip, and don't use ecstasy made by a lousy chemist.
- Tobacco Smoking - not only can it give you lung and air passage cancer, some components can pass through the placental wall and give your fetus increased risk of tumors.
- Ultraviolet Radiation - UVA, UVB, and UVC. Get the hell off of that tanning bed, yo!
- Vinyl Chloride - found in any town that has a plastic industry.