Tobacco smoke contains over 4,000 chemical compounds, many of which have been shown to be carcinogenic. For this reason, cigarette smoking has been strongly correlated with lung cancer. That, and this statistic: 90 percent of lung cancer cases are as a result of tobacco use.

But what of that other 10 percent? What else causes lung cancer?

Pipe and cigar smoking can also cause lung cancer, although the risk is not as high as with cigarettes. While someone who smokes one pack of cigarettes per day has a risk for the development of lung cancer that is 25 times higher than a nonsmoker, pipe and cigar smokers have a risk of lung cancer that is about five times that of a nonsmoker.

The inhalation of tobacco smoke from other smokers sharing the same space, is also an established risk factor for the development of lung cancer. Research has shown that nonsmokers who reside with a smoker have a 24 percent increase in risk for developing lung cancer when compared with other nonsmokers. An estimated 3,000 lung cancer deaths occur each year in the US that can be chalked up to passive smoking.

An estimated 12 percent of lung cancer deaths in the U.S. are attributable to radon gas, a chemically inert gas that is a natural decay product of uranium. Radon gas can travel up through soil and enter homes through gaps in the foundation, pipes, drains, or other openings. Radon gas is invisible and odorless, but can be detected with simple test kits. The U.S. Environmental Protection Agency estimates that one out of every 15 homes in the U.S. contains dangerous levels of radon gas.

Asbestos can kill in more ways than just mesothelioma. Cigarette smoking drastically increases the chance of developing an asbestos-related lung cancer in exposed workers. Asbestos workers who do not smoke have a fivefold greater risk of developing lung cancer than non-smokers, and those asbestos workers who smoke have a risk that is 50 to 90 times greater than non-smokers.

Genetic susceptibility is believed to play a role as to why not all smokers eventually develop lung cancer. So, too, doctors believe that a familial predisposition may be responsible for causing lung cancer in non-smokers.

Unfortunately, being a lung cancer survivor does not make you stronger and less likely to contract the disease again, it makes you more likely. Survivors of non-small cell lung cancers have an added risk of one to two percent per year for developing a second lung cancer. In survivors of small cell lung cancers, the risk for development of second cancers approaches six percent per year. Having or having had certain other lung disease, notably chronic obstructive pulmonary disease, predispose you to lung cancer as well.

Finally, up to one percent of of lung cancer deaths can be linked to air pollution. Experts believe that prolonged exposure to highly polluted air can carry a risk similar to that of passive smoking for the development of lung cancer.