Most lung cancer is caused by smoking. Over 85% of lung cancers are related to smoking.² Cancer-causing substances (carcinogens) in tobacco smoke damage lung cells. Over time, these damaged cells may develop into lung cancer.

The risk of getting lung cancer is related to how long you have smoked and how many cigarettes you smoke each day.³ Quitting smoking reduces your risk for getting cancer, and your risk continues to go down as long as you do not smoke. Even cutting down how much you smoke may reduce your risk (but not as much as quitting completely).⁴

If you live with a smoker, you have 2 to 3 times the risk of developing lung cancer compared with a person who lives in a nonsmoking environment.⁵ About 25% of nonsmokers who develop lung cancer probably get it from being exposed to secondhand smoke.³

Studies show that women have a similar risk of lung cancer as men.⁶ However, the chemicals in tobacco smoke may affect women differently than men.

Exposure to other harmful substances, such as asbestos, radioactive dust, or radon, increases the risk for lung cancer. Exposure to radiation such as X-rays later in life may also increase risk.⁷