Carcinogenic Viruses

Carcinogens are substances known to cause and promote cancer. Carcinogens can be either man-made, such as cigarette smoke, or present naturally in the environment, as is ultraviolet radiation from the sun, both of which are known to play a major role in the development of cancer. Carcinogens can also enhance other factors that cause the cancer. Certain cancers develop slowly. It can take from 5 to 40 years for cancer to develop after exposure to a cancer-causing agent, making identification of carcinogens difficult. The number of exposures as well as the length of time exposed to carcinogens determines whether a cancer will develop, but there is no evidence that there is a safe level of any carcinogen.