A trigger such as viral infection causes inflammation of the bronchial wall. This inflammation leads to mucosal thickening, epithelial cell desquamation, and denudation of the basement membrane.

An irritant causes an inflammatory response that leads to destruction of the alveolar air sacs, causing irreversible obstructive airway physiology.

Airway obstruction occurs due to the combination of inflammatory cell infiltration, mucus hypersecretion with mucus plug formation, and smooth muscle contraction.

The inflammatory response initiated by a viral or bacterial infection causes leakage of the alveolar-capillary membrane at the site of inflammation, causing a decrease in lung compliance and shortness of breath.