The main health risks in tobacco pertain to diseases of the cardiovascular system, in particular heart attack, cardiovascular disease, diseases of the respiratory tract such as Chronic Obstructive Pulmonary Disease (COPD), asthma, emphysema, and cancer, particularly lung cancer and cancers of the larynx and tongue.
A person's increased risk of contracting disease is directly proportional to the length of time that a person continues to smoke as well as the amount smoked.
However, if someone stops smoking, then these chances gradually decrease as the damage to their body is repaired. A year after quitting, the risk of contracting heart disease is half that of a continuing smoker. The health risks of smoking are not uniform across all smokers. Risks vary according to amount of tobacco smoked, with those who smoke more at greater risk. Light smoking is still a health risk. Likewise, smoking "light" cigarettes does not reduce the risks.
The data regarding smoking to date focuses primarily on cigarette smoking, which increases mortality rates :
** by 40% in those who smoke less than 10 cigarettes a day,
** by 70% in those who smoke 10–19 a day,
** by 90% in those who smoke 20–39 a day, and
** by 120% in those smoking two packs a day or more.
Pipe smoking has also been researched and found to increase the risk of various cancers by 33%.
Some studies suggest that hookah smoking is considered to be safer than other forms of smoking. However, water is not effective for removing all relevant toxins, e.g. the carcinogenic aromatic hydrocarbons are not water-soluble. Several negative health effects are linked to hookah smoking and studies indicate that it is likely to be more harmful than cigarettes, due in part to the volume of smoke inhaled. In addition to the cancer risk, there is some risk of infectious disease resulting from pipe sharing, and other risks associated with the common addition of other psychoactive drugs to the tobacco.
Diseases caused by tobacco smoking are significant hazards to public health. According to the Canadian Lung Association, tobacco kills between 40,000–45,000 Canadians per year, more than the total number of deaths from AIDS, traffic accidents, suicide, murder, fires and accidental poisoning. 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."
A new research has found that women who smoke are at significantly increased risk of developing an abdominal aortic aneurysm, a condition in which a weak area of the abdominal aorta expands or bulges.