Emphysema is a long-term (chronic), irreversible lung disease that occurs when the tiny air sacs in the lungs are damaged, usually as a result of long-term smoking. It causes difficulty breathing and shortness of breath that gets worse over time. Emphysema is often a type of chronic obstructive pulmonary disease (COPD).

A rare type of emphysema is caused by the lack of a substance in the lungs called alpha-1 antitrypsin. This type of emphysema is usually inherited.