an expulsive reflex initiated when the respiratory tract is irritated by infection, noxious fumes, dust, or other types of foreign bodies. The reflex results in a sudden expulsion of air from the lungs (lung) that carries with it excessive secretions or foreign material from the respiratory tract. Cough is beneficial; pneumonia frequently results when an effective cough reflex is lost as a result of chest injury, disease, or oversedation. Repeated and severe coughing, however, is physically exhausting and interferes with rest. Under these circumstances drugs may be used to suppress the reflex.

Cough occurs in many of the acute infectious diseases, including the common cold, in the majority of chronic pulmonary diseases, and frequently in heart disease. Any cough that persists longer than a few weeks should receive medical attention because it may be the first warning of serious disease.