You cough, but why? A cough is a reflex that helps your body clear your throat and lungs. A cough is a common symptom in people who have asthma, although it can occur for many other reasons, like when you have a cold. Someone who has asthma may cough because the airways are irritated (narrow, swollen, and filled with mucus). For some kids, coughing may be the only clue that they have asthma. The coughing may happen only at night or while exercising.