Title: Risk Factors for Cancer - Cancer - Merck Manuals Consumer Version
Headings: Risk Factors for Cancer
Risk Factors for Cancer
Family history
Genes and chromosomes
Age
Environmental factors
Geography
Diet
Drugs and medical treatments
Table
Some Carcinogens
Infections
Inflammatory disorders
Drugs Mentioned In This Article
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Content: Exposure to the radioactive gas radon, which is released from soil, increases the risk of lung cancer. Normally, radon disperses rapidly into the atmosphere and causes no harm. However, when a building is placed on soil with a high radon content, radon can accumulate within the building, sometimes causing levels in the air that are sufficiently high enough to cause harm. Radon is breathed into the lungs, where it may eventually cause lung cancer. In exposed people who also smoke, the risk of lung cancer is further increased. Many other substances have been investigated as possible causes of cancer, but more study is needed to identify those chemicals that increase the risk of cancer. Geography
The risk of cancer varies according to where people live, although the reasons for the geographic differences are often complex and poorly understood. This geographic variation in cancer risk is probably multifactorial: a combination of genetics, diet, and environment. For example, the risk of colon cancer and breast cancer is low in Japan, yet in Japanese people who immigrate to the United States, the risk increases and eventually equals that of the rest of the American population.