The health effects of smoking are the circumstances,
mechanisms, and factors of tobacco consumption on human health.
Epidemiological research has been focused primarily on cigarette tobacco
smoking,[1] which has been studied more extensively than any other form of consumption.[2]
Tobacco is the single greatest cause of preventable death globally.[3] Tobacco use leads most commonly to diseases affecting the heart, liver and lungs, with smoking being a major risk factor for heart attacks, strokes, chronic obstructive pulmonary disease (COPD) (including emphysema and chronic bronchitis), and cancer (particularly lung cancer, cancers of the larynx and mouth, and pancreatic cancer). It also causes peripheral vascular disease and hypertension.
The effects depend on the number of years that a person smokes and on
how much the person smokes. Starting smoking earlier in life and smoking
cigarettes higher in tar
increases the risk of these diseases. Also, environmental tobacco
smoke, or secondhand smoke, has been shown to cause adverse health
effects in people of all ages.[4] Cigarettes sold in underdeveloped countries
tend to have higher tar content, and are less likely to be filtered,
potentially increasing vulnerability to tobacco-related disease in these
regions.[5]
The World Health Organization (WHO) estimates that tobacco caused 5.4 million deaths in 2004[6] and 100 million deaths over the course of the 20th century.[7] Similarly, the United States Centers for Disease Control and Prevention
describes tobacco use as "the single most important preventable risk to
human health in developed countries and an important cause of premature
death worldwide."[8] Several countries have taken measures to control the consumption of tobacco with usage and sales restrictions as well as warning messages printed on packaging.
Smoke contains several carcinogenic pyrolytic products that bind to DNA and cause many genetic mutations. There are 45 known or suspected chemical carcinogens in cigarette smoke.[9] Tobacco also contains nicotine, which is a highly addictive psychoactive drug.
When tobacco is smoked, nicotine causes physical and psychological
dependency. Tobacco use is a significant factor in miscarriages among
pregnant smokers, and it contributes to a number of other threats to the
health of the fetus such as premature births and low birth weight and
increases by 1.4 to 3 times the chance for Sudden Infant Death Syndrome (SIDS).[10]
The result of scientific studies done in neonatal rats seems to
indicate that exposure to cigarette smoke in the womb may reduce the
fetal brain's ability to recognize hypoxic conditions, thus increasing the chance of accidental asphyxiation.[11] Incidence of impotence is approximately 85 percent higher in male smokers compared to non-smokers,[12] and is a key factor causing erectile dysfunction (ED).[12][13][14]