Carcinogens are substances, usually chemicals, that can cause cancer. Although chemical carcinogens are often linked with industry and technology, it is important to recognize that many carcinogens are naturally occurring substances.

Researchers have identified four factors, each of which is able to trigger cancer. These factors are chemicals, radiation (including ultraviolet radiation in sunlight), certain viruses, and inherited genes. In some cancer cases, more than one cause is responsible for generating the disease. For example, it is possible that certain chemicals might only cause cancer if a person has a genetic susceptibility to the disease or because there is a genetic error which prevents DNA repair.

Carcinogens are generally divided into two classes: those that are organic compounds and those that are inorganic compounds. Organic compounds always contain the element carbon. Chemicals in this class of carcinogens include solvents, certain pesticides, and naturally occurring chemicals produced by some...