Bronchitis

Bronchitis is an inflammation of the bronchial tubes, or bronchi, that bring air into the lungs. Inflammation is a chemical reaction in the body that produces redness, swelling, and pain.

Bronchitis can be caused by:
Viruses
Bacteria
Smoking
Breathing in certain kinds of irritating chemicals

When the cells lining the bronchi are irritated, the tiny hairs (cilia) that normally trap and eliminate things from the outside stop working. Formation of material associated with irritation (inflammation) also increases; causing the passages to become clogged.