Cigarette smoking is the main cause for developing lung cancer. Air pollution and industrial exposures also may cause problem to the lungs. Persons exposed to harmful substances, such as arsenic, asbestos, radioactive dust, and radon have a greater chance of developing lung cancer if they smoke. Not all smokers develop lung cancer and not all people with lung cancer are smokers.

The most significant cause of lung cancer is exposure to carcinogenic (cancer-causing) agents. Harmful substances, called carcinogens, in tobacco damage the lung cells. Squamous cell carcinoma and small cell carcinoma are the most common types found in smokers. Lung cancer in smokers is related with the age at which smoking began, how long the person has smoked, the number of cigarettes smoked per day, and how deeply the smoker inhales. Smoking at a younger age raises the risk and the death rate from lung cancer. Stopping smoking greatly reduces a person's risk for developing lung cancer.

Cigar and pipe smoking increases the risk of lung cancer but not as much as smoking cigarettes does. The chance of developing lung cancer is increased by exposure to environmental tobacco smoke or secondhand smoke- the smoke that non-smokers are exposed to when they share air space with someone who is smoking.

Radon, the radioactive gas found in substantial concentration in soil, rocks and some building materials, is considered to be the second leading cause of lung cancer. This is a detectable and preventable problem. Smokers are sensitive to the effects of radon. High radon levels in some mines can increase the lung cancer risk for miners.

Asbestos is another risk factor for lung cancer. If inhaled, asbestos particles can lodge in the lungs, damaging cells and increasing the risk for lung cancer. People who work with asbestos have a higher risk of getting Mesothelioma, cancer of the lining of the lung. If they smoke as well, the risk is greatly increased.

Certain lung diseases, such as tuberculosis (TB) and chronic obstructive pulmonary disease (COPD), increase a person's chance of developing lung cancer. Air pollution from motor vehicles, factories, and other sources may increase the risk for lung cancer, but it has not been established accurately. A person who has had lung cancer once is more likely to develop a second lung cancer compared with a person who has never had lung cancer. Contact with certain chemicals and substances, such as uranium, chromium and nickel, can cause lung cancer, but these are very rare causes. Certain reports indicate that diet low in fruits and vegetables may increase the chances of getting cancer, if you are exposed to tobacco smoke.