A carcinogen is any substance that is directly linked to the development of any type of cancer. Carcinogens can cause cancer in many ways, such as changing the cellular genome or interfering with metabolism. Among the best known carcinogens are inhaled asbestos, dioxin and tobacco smoke.
Radioactive materials are also potent carcinogens and can result in many different types of cancer depending on the cells that are damaged. This is a known risk of radiology that uses high-energy ionizing radiation.