Tobacco use most commonly leads to diseases affecting the heart and lungs, with smoking being a major risk factor for heart attacks, Chronic Obstructive Pulmonary Disease, emphysema, and cancer, particularly lung cancer, cancers of the larynx and mouth, and pancreatic cancer. Overall life expectancy is also reduced in regular smokers, with estimates ranging from 2.5 to 10 years fewer than nonsmokers. About half of male smokers will die of illness due to smoking. The association of smoking with lung cancer is strongest, both in the public perception and etiologically. People who have smoked tobacco at some point have about a one in ten chance of developing lung cancer during their lifetime. If one looks at men who continue to smoke tobacco, the risk increases to one in six. Historically, lung cancer was considered to be a rare disease prior to World War I and was perceived as something most physicians would never see during their career. With the postwar rise in popularity of cigarette smoking came a virtual epidemic of lung cancer.
A person’s increased risk of contracting disease is directly proportional to the length of time that a person smokes, as well as to the amount smoked, and doctors use the approximation “pack years” in assessing the likelihood of smoking-related illness. However, if someone stops smoking, then their risk declines over time, and the reduction in their lung function will stop.
In smoking, long term exposure to compounds found in the smoke such as carbon monoxide, cyanide, and so forth