Chronic obstructive pulmonary disease (COPD) is almost always the result of cigarette smoking. This link is so powerful that smoking cessation alone improves symptoms and can even reverse some lung damage. Most smokers seek medical help for their symptoms when they're in their late 40s or early 50s, after about 20 years of cigarette smoking has caused serious lung damage.

Smokers are 10 times more likely to die of COPD than are nonsmokers. In fact, 82 percent of people who die of COPD are smokers.

COPD can also be caused by smoking marijuana or by smoking cigars.

Exposure to chemicals and dusts in the workplace (such as coal mines and textile or metal-molding factories) increases the likelihood of COPD in people who smoke, but it usually does not cause COPD. Similarly, air pollution may worsen symptoms of COPD, but air pollution alone contributes far less to COPD than does cigarette smoking.

Only occasionally does a nonsmoker develop COPD as a consequence of environmental factors; even in such cases, the cause is usually secondhand smoke (from a smoker in the home).

A small number of nonsmokers develop emphysema because of an inherited disorder called alpha1-antitrypsin deficiency — a genetic defect that leads to lung destruction. Emphysema occurs earlier in people with this genetic defect if they smoke.