Emphysema is a long-term (chronic) lung disease. In emphysema, the tiny air sacs (alveoli) at the end of the airways in the lungs are damaged. When the air sacs are damaged or destroyed, their walls break down and the sacs become larger. These larger air sacs move less oxygen into the blood. This causes difficulty breathing or shortness of breath that gets worse over time. After air sacs are destroyed, they cannot be replaced.

Emphysema is a form of chronic obstructive pulmonary disease (COPD). It is usually caused by smoking. A rare type of emphysema is caused by the lack of a substance in the lungs called alpha1-antitrypsin. This type of emphysema is usually inherited.