Bronchiectasis (Bron-kee-ek-tas-is) is a condition characterized by physical changes in the airway structures that carry air and oxygen in and out of the lungs. The physical changes causing bronchiectasis involve areas of airway dilation (widening) and loss of elasticity, forming pouches (cavities) or scarring, all of which can trap mucus. Many of the changes are permanent.

Bronchiectasis can be treated, and symptoms can be improved, but it cannot be cured. As bronchiectasis progresses, usually over time, the airways lose some ability to move air in and out. This can prevent adequate levels of oxygen from reaching vital organs, leading to serious health problems. Mucus is a healthy substance produced in the lungs that remove inhaled dust, bacteria, and other small particles. However, in bronchiectasis, airways slowly lose their ability to clear mucus. When this happens, the mucus accumulates and creates an environment in which bacteria can flourish, leading to repeated, potentially serious lung infections and inflammation that further damage the airways.