Causes
The further narrowing of airways in people with chronic bronchitis that results in AECB can be caused by allergens (e.g., pollens, wood or cigarette smoke, pollution), toxins (a variety of different chemicals), or acute viral or bacterial infections.
Bacterial infections are usually associated with mucus that turns a yellow or greenish color and is typically much thicker than usual. Colored mucus does not necessarily mean the person has a bacterial infection, however.
When a person has severe chronic lung disease from smoking, it may take something as little as a chest cold to make their breathing so severe that they must be hospitalized.