A chemical substance or type of radiation that can cause cancer in exposed animals or humans. There is no single definition of the evidence necessary to classify a substance as a carcinogen. Four sources of evidence are used: EPIDEMIOLOGY, long term animal testing, short-term tests (such as the AMES TEST), and STRUCTURE-ACTIVITY RELATIONSHIPS. Separate guidelines and policies defining carcinogens have been used by the United States Environmental Protection Agency, the Occupational Safety and Health Administration, the Consumer Product Safety Commission, and the Food and Drug Administration. These agencies, and the International Agency for Research on Cancer, classify chemicals by the degree of evidence available as to their carcinogenicity…Carcinogens vary in their estimated ability to induce cancer