What causes emphysema?

Emphysema is caused by gradual damage and destruction of the alveoli, the tiny air sacs where oxygen enters the blood. As these air sacs lose their structure, the lungs have a harder time moving air and exchanging oxygen. Increased mucus production and sensitivity to irritants may occur in other respiratory conditions, but they are not the defining cause of emphysema.

AI-written and checked against the verified answer.