what is shortness of breath?
Shortness of Breath. Shortness of breath is defined as a âsubjective experience of breathing discomfort.â1 Along with cough, wheeze, and chest tightness, it is a typical symptom of asthma. In asthma, shortness of breath is usually caused by the narrowing of the airways. The airways become narrow for one or both reasons: 1  The muscles that surround the airways tighten up (âbronchospasmâ).  Inflammation makes the airways swell and fill with mucus.