What Is Emphysema?

Emphysema is a form of chronic (long-term) lung disease. People with emphysema have difficulty breathing from a limitation in blowing air out. There are multiple causes of emphysema, but smoking is by far the most common.

Emphysema is the main type of chronic obstructive pulmonary disease ( COPD). Although emphysema has no cure, quitting smoking reduces the rate of emphysema disease progression.

What Happens in Emphysema?

Emphysema results when the delicate linings of the air sacs in the lungs become irreversibly damaged. Most commonly, the toxins in cigarette smoke create the damage. Over years, the lung changes of emphysema slowly evolve:

• As the fragile tissues between air sacs are destroyed, air pockets in the lungs develop.
• Air becomes trapped in these spaces of damaged lung tissue.
• The lungs slowly enlarge, and breathing requires more effort.

This problem of emphysema is called airflow limitation. During lung function testing, it takes someone with emphysema far longer to empty their lungs than it does a person without emphysema.

Emphysema is the main form of chronic obstructive pulmonary disease (COPD). COPD is so named because people with emphysema exhale as if something were obstructing the flow of air. The other form of COPD is chronic bronchitis, which can also be caused by smoking.

Smoking Is a Major Cause of Emphysema

In the vast majority of people, smoking is the cause of emphysema. Exactly how smoking destroys the air sac linings in the lungs isn't known. However, population studies show that smokers are about six times more likely to develop emphysema than nonsmokers.

Estimates vary, but more than 10 million people in the U.S. likely have emphysema or another form of COPD. Emphysema and chronic bronchitis are the fourth leading cause of death in the U.S.

Interestingly, most heavy smokers do not develop emphysema. Why some smokers get emphysema and others do not is unknown. All heavy smokers experience other negative health effects of smoking, though.

Alpha-1 Antitrypsin Deficiency

Besides smoking, the other major known cause of emphysema is alpha-1 antitrypsin deficiency. However, this is a minor cause of emphysema, compared to smoking.

Alpha-1 antitrypsin (AAT) is a natural protein circulating in our blood. Its main function is to keep white blood cells from damaging normal tissues. White blood cells contain destructive substances they use to fight infections.

Some people -- perhaps 100,000 people in the U.S. -- have a genetic condition that makes them deficient in alpha-1 antitrypsin. Deficient levels of the AAT protein in the blood allow normal white blood cells to continuously damage lung tissue. If people with AAT deficiency smoke, the damage is even worse.

Over years, most people with severe AAT deficiency develop emphysema. It's not known how many people have emphysema caused by AAT deficiency. Experts estimate that about 2% to 3% of people with emphysema also have AAT deficiency.

Emphysema in AAT deficient patients has the same symptoms as emphysema caused by smoking. However, people with AAT deficiency often develop emphysema at a younger age. Liver problems may also occur in people with emphysema from AAT deficiency.

Secondhand Smoke and Other Potential Causes of Emphysema

Secondhand smoke may contribute to emphysema. Exposure to environmental cigarette smoke is known to damage the lungs. Several studies suggest that people exposed to high amounts of secondhand smoke are probably at higher risk for emphysema.

Air pollution is also believed to contribute to emphysema, although how much is unknown. Most people are exposed to pollution, and emphysema takes years to develop, making this effect hard to study.