Chronic bronchitis is a persistent inflammation of the bronchial tubes, airways leading to the lungs. The disease is characterized by a daily cough that produces sputum for at least three months each year for two consecutive years, when no other disease can account for these symptoms. The diagnosis of chronic bronchitis is made by this history, rather than by any abnormalities found on a chest x-ray or through a pulmonary function test.

When a person breathes in, air, smoke, germs, allergens, and pollutants pass from the nose and mouth into a large central duct called the trachea. The trachea branches into smaller ducts, the bronchi and bronchioles, which lead to the alveoli. These are the tiny, balloonlike, air sacs, composed of capillaries, supported by connecting tissue, and enclosed in a thin membrane. Bronchitis can permanently damage the alveoli.

Bronchitis is usually caused by cigarette smoke or exposure to...