There are a various risk factors that are linked to lung cancer. The most common known causes are as follows:

Cigarette Smoking
Cigarette smoking is probably the most closely related link to developing lung cancer. A person who smokes two packs or more of cigarettes per day has a one in seven chance of developing lung cancer. Those that smoke one pack of cigarettes per day have a twenty-five times greater chance of developing lung cancer than a non-smoker. In addition, those people that smoke a pipe or cigar have a five times greater chance of developing lung cancer than a non-smoker.

The risk of developing lung cancer increases with the number of cigarettes smoked over your lifetime. Cigarette smoking damages the cells in your lungs. The moment you stop smoking, your lungs begin healing themselves, replacing damaged cells with healthy, normal cells. Your risk of developing lung cancer begins decreasing almost immediately when you quit smoking. Every year that you do not smoke, your chances of developing lung cancer drop further. By the fifteenth year, your chances of developing lung cancer are about the same as those of a person who has never smoked.

Secondhand Smoke
Also known as passive smoking, people exposed to secondhand smoke on a regular basis will have a higher risk of developing lung cancer, even if they do not smoke themselves. Studies have shown that those who live with a smoker have a 24% greater risk of developing lung cancer than most non-smokers. Doctors estimate that about 3000 lung cancer deaths a year are related to secondhand smoke.

Asbestos Exposure
Exposure to asbestos is another well-known cause of lung cancer and mesothelioma - cancer of the pleural lining of the lungs. Asbestos was widely used in construction and everyday products in the late 1800s through the 1960s. Asbestos separates into fine silica fibers that become trapped in the tissues of the lungs. Mesothelioma is inextricably linked to asbestos exposure. There are no reported cases of mesothelioma in people who were not exposed to asbestos either in the workplace or through their environment. A non-smoker who was exposed to asbestos has a five times greater risk of developing lung cancer than a non-smoker who was not exposed. Smoking increases the risk dramatically - a smoker who was exposed to asbestos has a risk of developing lung cancer that is 50 to 90 times greater than that of a non-smoker.

Radon Gas
It is estimated that about 12% of lung cancer deaths can be attributed to radon gas, a colorless, odorless gas that is a natural byproduct of the decay of uranium. The U.S. Environmental Protection Agency estimates that as many as 15% of homes in the United States have unsafe levels of radon gas, which will account for 15,000 to 22,000 deaths from lung cancer annually.

Air Pollution
Scientists estimate that as many as 1% of all lung cancer deaths are attributable to air pollution. They believe that prolonged exposure to very polluted air can raise the risks of developing lung cancer to about the levels of a passive smoker.