If a smoker stops smoking, performance is measurably increased even after as little as 24 hours of not smoking. Chronic smoking also damages the lungs so that the surface area where gas exchange takes place is reduced. This damage is permanent, even if they stop smoking. Of more immediate concern to smoking divers, this process breaks down the walls between the alveoli, resulting in the formation of air sacks or bulla. One fascinating study I found looked at divers who had experienced neurological signs and symptoms within five minutes of surfacing from a normal dive.
Cigarette smoke contains hundreds of chemicals that are known to cause cancer.
These chemicals build up in the body of a smoker and not surprisingly, smokers develop many more cancers than nonsmokers. Lung cancer is most common but smokers also have a much higher risk of other cancers. We also know that smokers have a much higher risk of heart attack and stroke than nonsmokers. The exact mechanism for this effect is not known but the association is inarguable. In conclusion, smoking has hundreds of damaging and detrimental effects on the body.