COPD is almost always caused by smoking. Most people with COPD have smoked for a long time. And research shows that smoking cigarettes puts you at risk for COPD. Over time, breathing tobacco smoke irritates the airways and damages the lungs.

People who get emphysema in their 30s or 40s may have a disorder that runs in families, called alpha-1 antitrypsin deficiency. This is a rare condition in which your body may not be able to make enough of a protein (alpha-1 antitrypsin) that helps protect the lungs from damage.