Smoking is by far the number one cause of lung cancer .
Over time, the harmful chemicals in tobacco cause damage to lung tissue. With repeated exposure to these chemicals, the likelihood that an individual will develop lung cancer increases. Cigar and pipe smokers are also at greater risk than nonsmokers for developing lung cancer. The risk of developing lung cancer from tobacco use is related to the age at which smoking began, how many years the person has smoked, the number of cigarettes or packs per day that a smoker uses, and how deeply the smoker inhales. Overall, men who smoke are estimated to be 22 times more likely to develop lung cancer, while women who smoke are estimated to be 12 times more likely.