what is a carcinogen

A carcinogen is a substance, organism, or agent that can cause cancer. Carcinogens may occur naturally in the environment, such as ultraviolet rays in sunlight, or may be generated by humans, such as automobile exhaust fumes and cigarette smoke. Most carcinogens work by interacting with a cells DNA to produce mutations. There are more than 100 known carcinogens, including asbestos, tobacco, and ultraviolet rays from the sun. However, exposure to a carcinogen does not necessarily mean that a person will develop cancer. A number of factors influence whether a person exposed to a carcinogen will ultimately develop cancer, including the amount and duration of the exposure, exposure to other environmental factors, and genetic makeup. The US Department of Health and Human Services National Toxicology Program and the World Health Organizations International Agency for Research on Cancer both use evidence-based approaches to catalog substances that are known or reasonably anticipated to be human carcinogens. To date, over 500 substances have been identified as definitive, probable, or possible carcinogens for humans. If a substance or exposure has been labeled a carcinogen, it means it has been studied extensively by researchers, and one or more agencies have evaluated the evidence and determined it to be a cause of cancer.