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Updated October 20, 2009

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Definition: a substance that causes or promotes cancer. Exposure to a carcinogen can occur via the environment, chemicals and viruses. Carcinogens are categorized in different levels, based on their potential to cause cancer in humans.

Many chemical additives in cigarettes are considered to be carcinogenic, which greatly increases the risk of many types of cancer in people who smoke. The Epstein-Barr virus is an example of a viral carcinogen, as it increases the risk of lymphoma. Radon is a significant environmental exposure that can lead to lung cancer.

Exposure to a carcinogen doesn't mean you will absolutely develop cancer. There are many factors involved, such as the type of carcinogen, how long you were exposed, and the frequency of exposure.

Pronunciation: kar-SIN-o-jin
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