From the physiological point of view, cough is a forced expulsion of air from the lungs. Cough may be a reflex or a voluntary action.
By coughing, we forcibly expel air from the lungs and by doing so free the airways from material which may be present: mucus, pathogenic agents and inhaled substances which may be harmful or irritating. Cough is a primary defense mechanism for protecting the airways and is essential for ensuring good physiological function of the respiratory system.