Smoking is the number one cause of lung cancer.
Cigarette smoke contains more than 4,000 different chemicals, many of which are proven carcinogens, while hundreds of others increase the cancer-causing power of carcinogens. The more you smoke and the longer you smoke, the greater your risk of lung cancer. But if you stop smoking, the risk of cancer decreases steadily each year as abnormal cells are replaced by normal cells. In ten years, the risk decreases to a level that is 30 to 50 percent of the risk for people who continue to smoke. In addition, quitting smoking dramatically reduces the risk of developing other smoking-related diseases, such as heart disease and stroke, and significantly reduces the risk of serious emphysema and chronic bronchitis.