Thirty percent of men and 19 percent of women around the world smoke. One hundred thousand children under the age of 15 start smoking every day. One of every ten deaths around the world is caused by a smoking-related disease. With statistics like this, it's hard to imagine why smoking continues to be so widespread.

There are over 4,000 chemicals in a single cigarette, some of which are highly poisonous. Examples include naphthalene, which is used in moth repellent; acetone, the main component of nail polish remover; butane, a constituent of lighter fluid; and formaldehyde, used in embalming. Cigarettes also contain nicotine, a highly addictive stimulant that causes physical and psychological dependency.

The two most serious health effects of smoking are cancer and emphysema. Smoking has been linked to 11 forms of cancer, including cancer of the esophagus, mouth, pancreas, bladder, and kidney. According to recent studies, smokers are 26 times more likely to die of lung cancer than non-smokers. Emphysema is a chronic disease that destroys parts of the lungs and results in shortness of breath, hyperventilation, and asthma-like attacks.

Another common health effect of smoking is coronary artery disease. Smoking reduces the amount of oxygen that reaches the heart, increases blood clotting and blood pressure, and decreases high-density lipoprotein (HDL) or "good" cholesterol. Women taking oral contraceptives should not smoke, as the risk for stroke increases almost four times.

Other possible side effects of smoking include cataracts, reduced fertility, a higher risk of stroke, peptic ulcers, and back pain. Pregnant women who smoke are at risk for miscarriages, premature labor, and ectopic pregnancy. Babies born to mothers who smoke have a higher risk of sudden infant death syndrome (SIDS) and behavioral problems later in life.

Smoking has some unpleasant cosmetic effects too. Smokers often suffer from bad breath, yellowing teeth and nails, and early wrinkles around the mouth. Smoking causes changes in the coloring and texture of the skin, often resulting in an ashy complexion. A smoker is also three times more likely to lose teeth than a non-smoker.

Passive smoking, also known as second-hand smoke, can be just as deadly, especially for children, pregnant women, and non-smoking adults.