Asthma symptoms occur due to airway inflammation resulting from hypersensitivity to foreign proteins, allergens, or even temperature changes.

Allergens trigger an immune response. The antibody immunoglobulin E (IgE) is released to defend the body from the allergen. The IgE binds to the allergen and brings it to a mast cell, a type of immune cell, which triggers an inflammatory response. Histamine and other substances are released, causing mucus to fill the airways, coughs, wheezes, and the inability to breathe.

Airways may constrict from excessive or prolonged muscle contraction, referred to as bronchoconstriction. Airway diameter decreases, restricting the space available for air movement. Afflicted individuals are deprived of oxygen. In the most extreme cases, individuals risk brain damage or death due to oxygen deprivation.