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). People who have asthma may cough because their airways are irritated (narrow and swollen). For some people, coughing may be the only clue that they have asthma. The coughing may happen only at night or while exercising.