What comes to mind when someone tells you that smoking is dangerous? Lung cancer? Birth defects? Emphysema? Well, it's a bit more complicated than that; a lot more, in fact. Smoking affects nearly every organ in the body and can cause serious health problems:

• Leukemia
• Cataracts
• Cancer
• Pneumonia
• Gum disease
• Heart disease
• Emphysema
• Peptic ulcers
• Aortic aneurysm (swelling of an artery)
• Osteoporosis (weak bones)
• Increased risk of wound infections after surgery
• Problems getting pregnant and carrying a baby

It's little wonder that tobacco causes so many problems. Tobacco has more than 4,000 chemicals, with more than 60 known to cause cancer. Some of these substances include ammonia, tar, arsenic, lead and carbon monoxide.

Smoking kills half a million people each year and is blamed for one third of all cancers. Smoking can cause cancer of the mouth, throat, lung and bladder. Besides cancer, smoking can affect your body in many other ways.

Your lungs

Smokers get colds and respiratory infections more easily than nonsmokers. Plus, when you smoke, you inhale poison. These poisons damage the membranes lining the inside of your lungs. Over the years, a smoker's lungs become very thick, black and scarred. Tiny hairs that clean your lungs of dust cannot work as well, which can lead to infection. Such damage can cause emphysema, in which the air sacs in the lungs become so large that is difficult to breathe.

Because emphysema destroys air sacs, the lungs transfer less oxygen to the bloodstream, causing shortness of breath. The lungs also lose their elasticity, so patients experience difficulty exhaling. Early symptoms include shortness of breath and coughing.

Asthma and smoking can be a deadly mix because smoking is extremely harmful to the respiratory system. Asthma is a potentially life-threatening disease of the bronchial tubes, the airways that branch into the lungs. The airways of a person with asthma are sensitive and can be triggered by allergens and smoke. When a person inhales tobacco smoke, irritating substances settle in the lining of the airways and can set off asthma attacks.

Your heart and brain

A smoker's risk of heart attack is more than twice that of a nonsmokers', according to the American Heart Association. The chemicals from cigarettes damage blood vessel walls, leading to high blood pressure. High blood pressure directly increases the risk of coronary heart disease, heart attack and stroke, especially when combined with other risk factors. Because of the effects smoking has on the body, it becomes harder to exercise and strengthen your heart.

Cigarette smoking is the biggest risk factor for sudden cardiac death. Smokers have two to four times the risk of nonsmokers. Smokers who have a heart attack also are more likely to die suddenly, within an hour of the attack. Cigarette smoking acts with other factors to greatly increase the risk for coronary heart disease. People who smoke cigars or pipes seem to have a higher risk of death from coronary heart disease (and possibly stroke), but their risks aren't as great as those of cigarette smokers.

If you have diabetes, constricted blood vessels from smoking can worsen foot ulcers and lead to blood vessel disease and leg and foot infections. People with diabetes who smoke are three times more likely to die of cardiovascular disease than nonsmokers with diabetes. Smokers with diabetes are more likely to get nerve damage and kidney disease, too.

Smoking also can cause an abdominal aortic aneurysm, which is an artery that balloons outward. This can kill you. The chemicals from cigarettes damage blood vessel walls, too, leading to high blood pressure and a greater risk for blood clots.

Your digestive system

Smoking can increase the risk for peptic ulcers, which are sores in the stomach and intestines. Ulcers in smokers tend to be more severe than in nonsmokers and more likely to kill. Heartburn and acid reflux happen more in smokers and are more severe. Also, the liver cannot process medications as well as it should.

Your teeth and gums

Researchers believe smokers are more likely than nonsmokers to develop gum disease because of their poor immune systems.

Your bones

The exact relationship between smoking and brittle bones is not yet clear. It's possible that smokers have higher risk factors for osteoporosis than nonsmokers because they tend to be thinner, drink more alcohol, exercise less and follow less-healthy diets. Smoking increases the risk of limited joint mobility.

Your looks

If health problems aren't enough to scare you, consider your appearance. Smoking increases skin wrinkles and stains your teeth and fingers. Researchers believe smoking reduces blood flow to the skin. This means vitamins (such as vitamin A, which reduces sun damage) have a harder time reaching the skin's surface.

Your chances for having a healthy baby

The chemicals in cigarettes make it harder to become pregnant and even affect sperm counts. If you smoke during pregnancy, it can interfere with the baby's supply of oxygen. This increases your risks for miscarriage, premature delivery and having a low-birth-weight baby.

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External Sources American Heart Association Centers for Disease Control and Prevention American Lung Association American Cancer Society U.S. Surgeon General

This article was reviewed and updated June 2007.