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Environmental causes probably account for well over half of all typers of cancer cases. Most environmental risks are determined by lifestyle choices (smoking, diet, etc.), while the rest arise in community and workplace settings. The degree of cancer hazard posed by these voluntary and involuntary risks depends on the concentration or intensity of the carcinogen and the exposure dose a person received. In situations where high levels of carcinogens are present and where exposures are extensive, significant hazards may exist, but where concentrations are low and exposures limited, hazards are often negligible. When low-dose exposures persist over time they can represent significant public health hazards (for example, exposure to secondhand tobacco smoke). Cancer prevention starts by eliminating known environmental risks such as smoking and other exposures to high level carcinogens. Various chemicals (for example, benzene, asbestos, vinyl chloride, arsenic, aflatoxin) show definite evidence of human carcinogenicity; others are considered probable human carcinogens based on evidence from animal experiments (for example, chloroform, dichlorodiphenyl-trichloroethane [DDT], formaldehyde, polychlorinated biphenyls [PCBs], polycyclic aromatic hydrocarbons). Often in the past, direct evidence of human carcinogenicity has come from studies of workplace conditions involving sustained, high-dose exposures. Risks can be increased when particular exposures occur together (for example, asbestos exposure and cigarette smoking). Many different types of cancer can be caused by environmental factors. The best cancer prevention is to eliminate as many of these known risk factors from your every day life as possible.
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