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Carcinogens

Substances capable of causing cancer.

The U.S. Environmental Protection Agency (EPA) classifies many substances on the basis of their potential for causing cancer. Classifications are based on results of studies on animals, or with humans. Classification categories refer to epidemiological studies, which are studies to identify the factors controlling the presence or absence of a disease.

Group A or Human Carcinogens. There is a relationship between the substance and cancer that has been shown through epidemiological studies on humans.

Group B or Probable Human Carcinogen. There are two types of carcinogens in this category. There is sufficient evidence from animal studies and limited epidemiological studies that B1 carcinogens cause cancer. B2 carcinogens are classified on the basis of sufficient evidence from animal studies only; epidemiological data are inadequate or nonexistent.

Group C or Possible Human Carcinogens. Classification in this category is based on limited evidence from animal studies and no epidemiological data.

Group D or Not Classifiable as to Human Carcinogenicity. The studies on substances in this category are inadequate or completely lacking, so no assessment of the substance's cancer-causing potential is possible.

Group E or Evidence of Noncarcinogenicity for Humans. Substance in this category have tested negative in at least two adequate animal cancer tests in different species and in adequate epidemiological and animal studies.

For Further Study

Books

U.S. Department of Health and Human Services, Public Health Service, Seventh Annual Report on Carcinogens, Summary 1994. National Institute of Environmental Health Sciences: Research Triangle Park, North Carolina, 1995. Contact the National Institute of Environmental Health Sciences Publications Office, (919) 541-3419.