Smoking tobacco is the biggest risk factor for lung cancer. The more a person smokes, the greater the risk of suffering from lung cancer. If a person stops smoking, the risk decreases. But the risk is higher in those who have been smokers than in those who have never smoked. And the risk of lung cancer is greater among people exposed to second-hand smoke than in people without any exposure to smoke.

Uranium — a substance found in rocks and soil — is a cancer-causing agent. Miners of uranium have a high risk of developing lung cancer. As uranium decays, a gas called radon is produced and gets into air and water, and it can accumulate in buildings, including homes. The risk of lung cancer depends on how much radon is in the home.

Other agents which can cause lung cancer are asbestos, arsenic, beryllium, cadmium, chromium, nickel, coal smoke, soot, silica and diesel fumes.

There are two lung diseases which can increase the risk of lung cancer: chronic obstructive pulmonary disease (COPD) and the widespread pulmonary fibrosis.

The risk of lung cancer is higher in smokers with a family history of smoking, especially when there are several cases in the family.

The risk of lung cancer may be increased in people with a smoking-related cancer (stomach, bladder, kidney, pancreatic, cervical, or head and neck cancers, or acute myeloid leukaemia) and in people who have had lymphoma.