It takes only a few packs of cigarettes for smokers' blood to contain up to 15 times as much CO as nonsmokers' blood. Less oxygen reaches the brain and muscles, slowing athletes' reaction times and impairing their energy, strength, and coordination. Meanwhile, the nicotine in smoke boosts the heart rate, increasing the body's need for oxygen. That's why smokers become short of breath so easily. Their bodies need more oxygen, but their blood carries less.
Every puff exposes smokers to gases that irritate the eyes, nose, throat, and gums.
Continued smoking spurs a thickening of the throat lining, eventually leading to throat cancer. Smokers are also at increased risk of gum disease and tooth loss. As in the throat, the body thickens the bronchial lining, trying to protect it from smoke. The process eventually causes lung cancer. Smoking progressively impairs the lungs' ability to oxygenate the blood, leading to emphysema.