Health effects of smoking

The health effects of tobacco are the circumstances, mechanisms, and factors of tobacco consumption on human health. Epidemiological research have been focused primarily on tobacco smoking, which has been studied more extensively than any other form of consumption. As of 2000, smoking is practiced by some 1.22 billion people, of which men are more likely to smoke than women, however the gender gap declines with age, poor more likely than rich, and people of developing countries than those of developed countries.

Fresh tobacco, processed tobacco, and tobacco smoke contain carcinogens. The current view on cancer is that carcinogenicity is a stochastic effect, where various environmental factors trigger the development of cancer. While exposure to a carcinogen increases the probability of cancer, the process remains random. For example, smoking tobacco is known to cause cancer in humans, but not all people who smoke necessarily develop smoking-related cancer. Jeanne Calment, for example, with the longest confirmed lifespan of 122 years, smoked until she was 117, and included cigarettes as her prescription for a long life. Additionally, in studies on humans, the large number of confounding variables makes it challenging to statistically distinguish their effects.

Tobacco use leads most commonly to diseases affecting the heart and lungs, with smoking being a major risk factor for heart attacks, strokes, Chronic Obstructive Pulmonary Disease (COPD),emphysema, and cancer.