airway hyperresponsiveness

Think of two people walking into a smoky room: one shrugs it off, while the other's airways slam half-shut within minutes. That over-reactive, hair-trigger response is airway hyperresponsiveness — airways that narrow far too much, and far too easily, to stimuli that barely bother normal lungs.

Physiologically, it describes an exaggerated bronchoconstrictor response of airway smooth muscle to triggers such as cold air, exercise, allergens, smoke, or inhaled challenge agents like methacholine or histamine. It is a defining feature of asthma and reflects both twitchy smooth muscle and underlying airway inflammation that primes the airways to overreact.

It can be measured objectively with a bronchial challenge test, where the dose needed to drop FEV1 by a set amount indicates how sensitive the airways are. Hyperresponsiveness is not unique to asthma — it can appear after viral infections or in some people with allergic rhinitis or COPD — so it supports, but does not by itself prove, an asthma diagnosis.