This is a medical question of type : causes 
 What causes Lung Cancer ? 
 Tobacco Products and Cancer Using tobacco products has been shown to cause cancer. In fact, smoking tobacco, using smokeless tobacco, and being exposed regularly to secondhand tobacco smoke are responsible for a large number of cancer deaths in the U.S. each year. Cigarette Smoking Causes Lung Cancer Cigarette smoking is the number one cause of lung cancer. Scientists have reported widely on the link between cancer and smoking since the 1960s. Since then, study after study has provided more proof that cigarette smoking is the primary cause of lung cancer. Before cigarette smoking became popular after World War I, doctors rarely, if ever, saw patients with lung cancer. But today, lung cancer is the leading cause of death by cancer. Over 85 percent of people with lung cancer developed it because they smoked cigarettes. If You Smoke If you smoke cigarettes, you are at much higher risk for lung cancer than a person who has never smoked. The risk of dying from lung cancer is 23 times higher for men who smoke and 13 times higher for women who smoke than for people who have never smoked. Lung cancer can affect young and old alike.  Stopping smoking greatly reduces your risk for developing lung cancer. After you stop, your risk levels off. Ten years after the last cigarette, the risk of dying from lung cancer drops by 50 percent -- which does not mean, however, that risk is eliminated. (Watch the videos on this page to learn more about lung cancer, smoking and older adults. To enlarge the videos, click the brackets in the lower right-hand corner of the video screen. To reduce the videos, press the Escape (Esc) button on your keyboard.) Smoking cigars and pipes also puts you at risk for lung cancer. Cigar and pipe smokers have a higher risk of lung cancer than nonsmokers. Even cigar and pipe smokers who do not inhale are at increased risk for lung, mouth, and other types of cancer. The likelihood that a smoker will develop lung cancer is related to the age smoking began; how long the person smoked; the number of cigarettes, pipes, or cigars smoked per day; and how deeply the smoker inhaled.  Learn about lung cancer prevention. Other Factors That Increase Your Risk - Many studies suggest that non-smokers who are exposed to environmental tobacco smoke, also called secondhand smoke, are at increased risk of lung cancer. Secondhand smoke is the smoke that non-smokers are exposed to when they share air space with someone who is smoking. Tobacco smoke contains more than 7,000 chemicals, including hundreds that are toxic and about 70 that can cause cancer. Since 1964, approximately 2,500,000 nonsmokers have died from health problems caused by exposure to secondhand smoke.   - Exposure to radon can put a person at risk for lung cancer, too. People who work in mines may be exposed to this invisible, odorless, and radioactive gas that occurs naturally in soil and rocks. It is also found in houses in some parts of the country. A kit available at most hardware stores allows homeowners to measure radon levels in their homes.   - Another substance that can contribute to lung cancer is asbestos. Asbestos has been used in shipbuilding, asbestos mining and manufacturing, insulation work, and brake repair, although products with asbestos have been largely phased out over the past several decades. If inhaled, asbestos particles can lodge in the lungs, damaging cells and increasing the risk for lung cancer.  Many studies suggest that non-smokers who are exposed to environmental tobacco smoke, also called secondhand smoke, are at increased risk of lung cancer. Secondhand smoke is the smoke that non-smokers are exposed to when they share air space with someone who is smoking. Tobacco smoke contains more than 7,000 chemicals, including hundreds that are toxic and about 70 that can cause cancer. Since 1964, approximately 2,500,000 nonsmokers have died from health problems caused by exposure to secondhand smoke. Exposure to radon can put a person at risk for lung cancer, too. People who work in mines may be exposed to this invisible, odorless, and radioactive gas that occurs naturally in soil and rocks. It is also found in houses in some parts of the country. A kit available at most hardware stores allows homeowners to measure radon levels in their homes. Another substance that can contribute to lung cancer is asbestos. Asbestos has been used in shipbuilding, asbestos mining and manufacturing, insulation work, and brake repair, although products with asbestos have been largely phased out over the past several decades. If inhaled, asbestos particles can lodge in the lungs, damaging cells and increasing the risk for lung cancer. It's Never Too Late To Quit  Researchers continue to study the causes of lung cancer and to search for ways to prevent it. We already know that the best way to prevent lung cancer is to quit or never start smoking. The sooner a person quits smoking the better. Even if you have been smoking for many years, it's never too late to benefit from quitting. Get Free Help To Quit Smoking - Each U.S. state and territory has a free quit line to provide you with information and resources to help you quit smoking. To reach the quit line in your area, dial toll-free, 1-800-QUIT-NOW (1-800-784-8669). Each U.S. state and territory has a free quit line to provide you with information and resources to help you quit smoking. To reach the quit line in your area, dial toll-free, 1-800-QUIT-NOW (1-800-784-8669). - Talk with a smoking cessation counselor from the National Cancer Institute (NCI) for help quitting and for answers to smoking-related questions in English or Spanish. Call toll free within the United States, Monday through Friday 8:00 a.m. to 8:00 p.m. Eastern Time.1-877-44U-QUIT (1-877-448-7848) Talk with a smoking cessation counselor from the National Cancer Institute (NCI) for help quitting and for answers to smoking-related questions in English or Spanish. Call toll free within the United States, Monday through Friday 8:00 a.m. to 8:00 p.m. Eastern Time.1-877-44U-QUIT (1-877-448-7848) - Get free information and advice about quitting smoking through a confidential online text chat with an information specialist from the National Cancer Institute's Cancer Information Service. Visit LiveHelp, available Monday through Friday, 8:00 a.m. to 11:00 p.m. Eastern Time. Get free information and advice about quitting smoking through a confidential online text chat with an information specialist from the National Cancer Institute's Cancer Information Service. Visit LiveHelp, available Monday through Friday, 8:00 a.m. to 11:00 p.m. Eastern Time. You can also get help to quit smoking at these websites. - Smokefree.gov.  - Smokefree Women  Smokefree.gov. Smokefree Women For adults 50 and older, check out Quitting Smoking for Older Adults.