Many types of cancer are caused by exposure to carcinogenic (cancer-causing) substances that can be avoided. For example, quitting smoking reduces the risk of cancer. Other lifestyle changes, such as eating a healthy diet, can reduce risks. The cause of many cancers is not yet known.

Lung Cancer

Cigarette smoking causes 90 percent of lung cancers. If a person stops smoking, their risk of getting cancer decreases right away.  With time, that person’s risk becomes nearly the same as the risk for non-smokers.

A small percentage of people may get lung cancer even if they don’t smoke. They may have a family history. Other reasons exist that are unclear.

Other Types of Cancer

Other things increase the risk of cancer. They relate to chemicals, the environment, or lifestyle, such as:

• Chemicals, like pesticides that kill bugs and weeds
• Too much alcohol
• Too much sunlight (skin cancer)
• Obesity
• Radiation exposure
• Some viruses like those related to cervical and liver cancer

Last Updated May 2023