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. This is because the extra mucus in the airways of a person with chronic bronchitis provides a good place for viruses and bacteria to grow. 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.