If the cough is caused by a common cold, most of them will be cured within 7 days. Colds are mainly caused by viral infections and are self-limiting. However, if the cough is caused by bronchitis or pneumonia, active treatment is needed and the cough will improve within a week or so through active treatment. If not treated in time, the symptoms will worsen and the cough will last longer. If the cough is caused by mycoplasma infection, it may take longer than other bacterial and viral infections, and it may improve in about half a month.