One of the most important cause of cancer is smoking. Smoking increases the risk of lung cancer, mouth, larynx, and bladder. Chemical substances contained in cigarettes is the most dangerous and can cause cancer:
- Asetonnitrit and dioxins
- Nitrogen gas that causes a carcinogenic nitrosamines
- Substance polynuclear aromatic hydrocarbons (PAHs) contained in the tar, a carcinogen and DNA damage
- Carcinogenic acetaldehyde, primarily in the skin
Excessive exposure to ultraviolet sun rays can cause skin cancer. Radiation at the uranium miners have been associated with the occurrence of lung cancer 10-20 years later. Higher risk if the miners also smoked.
Ionizing radiation (which is a carcinogen) is used in X-ray, generated from nuclear power plants and atomic bombs and can reach very long distances. For example, people who survived the atomic bombs on Hiroshima and Nagasaki in World War II, a high risk of cancer of blood cells, such as leukemia.