Tobacco is the single greatest cause of preventable death in the world. 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(particularly lung cancer, cancers of the larynx and mouth, and pancreatic cancer).
It also causes peripheral vascular disease and hypertension, all developed due to the exposure
time and the level of dosage of tobacco. Furthermore, the earlier and the higher level of
tar content in the tobacco filled cigarettes causes the greater risk of these diseases.
Cigarettes sold in developing nations tend to have higher tar content, and are less likely
to be filtered, potentially increasing vulnerability to tobacco-related disease in these regions.

The World Health Organization (WHO) estimates that tobacco caused 5.4 million deaths
in 2004 and 100 million deaths over the course of the 20th century. 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.

Smoke contains several carcinogenic pyrolytic products that bind to DNA and cause many
genetic mutations. There are over 19 known chemical carcinogens in cigarette smoke.
Tobacco also contains nicotine, which is a highly addictive psychoactive chemical.
When tobacco is smoked, nicotine causes physical and psychological dependency.

Tobacco use is a significant factor in miscarriages among pregnant smokers. 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). The result of scientific studies done in neonatal rats seems to indicate
that exposure to cigarette smoke in the uterus (womb) may reduce the fetal brain's ability
to recognize hypoxic conditions, thus increasing the chance of accidental asphyxiation.
Incidence of impotence is approximately 85 percent higher in male smokers compared
to non-smokers, and is a key factor causing erectile dysfunction (ED).