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Why does asthma cause wheezing?

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Medical illustration of the human chest showing the lungs, diaphragm, ribs, trachea, bronchus, and bronchioles, with one lung cut away to reveal internal structures. — respiratory disease The bronchioles of the lungs are the site where oxygen is exchanged for carbon dioxide during the process of respiration. Inflammation, infection, or obstruction of the bronchioles is often associated with acute or chronic respiratory disease, including bronchiectasis, pneumonia, and lung abscesses.

Asthma causes wheezing because it is a chronic disorder characterized by the inflammation and constriction of the airways. When an individual is exposed to an inciting factor, the immune system releases chemicals that trigger three primary physiological responses:1

Smooth muscle contraction: The smooth muscle surrounding the bronchi undergoes spasmodic contraction.21
Inflammation: The bronchial tubes become swollen and inflamed.1
Mucus production: There is an excessive secretion of viscous mucus into the airways.21

These factors combine to obstruct the bronchial tree, often acting as a one-way valve where air can be inspired but not easily expired. This significant airflow obstruction results in the characteristic whistling or wheezing sound as air is forced through the narrowed, mucus-clogged passages.21