Carcinogen: A substance or agent that causes cancer. Related terms include the adjective “carcinogenic” and the nouns “carcinogenesis” and “carcinogenicity.” One of the best-known carcinogens is ionizing radiation.

The International Agency for Research on Cancer has classified some 60 substances and processes as probably or definitely carcinogenic in humans. These substances and processes are divided into three categories — Agents and groups of agents, Mixtures, and Exposure circumstances — and they are as follows:

Agents and groups of agents

Aflatoxins, naturally occurring
Arsenic and arsenic compounds
Beryllium and beryllium compounds
N,N-Bis(2-chloroethyl)-2-naphthylamine (chlornaphazine)
Bis(chloromethyl) ether and chloromethyl methyl ether
1,4-Butanediol dimethanesulfonate (busulfan; Myleran)
Cadmium and cadmium compounds
1-(2-Chloroethyl)-3-(4-methylcyclohexyl)-1-nitrosourea (methyl-CCNU; Semustine)
Chromium [VI] compounds
Ethylene oxide
Methoxypsoralen (methoxsalen) plus ultraviolet radiation
MOPP and other combined chemotherapy including alkylating agents
Mustard gas (sulfur mustard)
Nickel compounds
Estrogen therapy, postmenopausal
Radon and its decay products
Silica, crystalline
Solar radiation
Talc-containing asbestiform fibers
Vinyl chloride


Alcoholic beverages
Analgesic mixtures containing phenacetin
Betel quid with tobacco
Coal-tar pitches
Coal tars
Mineral oils, untreated and mildly treated
Salted fish (Chinese style)
Shale oils
Tobacco products, smokeless
Tobacco smoke
Wood dust

Exposure circumstances

Aluminum production
Auramine manufacturing
Boot and shoe manufacture and repair
Coal gasification
Coke production
Furniture and cabinet making
Hematite mining (underground) with exposure to radon
Iron and steel founding
Isopropanol manufacturing (strong-acid process)
Magenta manufacturing
Painting (occupational exposure)
Rubber industry
Strong-inorganic-acid mists containing sulfuric acid (occupational exposure)

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