Cough is a reflex that protects the lungs from aspirating food or inhaling irritants. It is a key component of the nonimmune pulmonary defense system. The cough that accompanies most common respiratory infections usually resolves in 7 to 10 days and rarely is a cause of concern. The patient who has frequent viral infections may complain of a "chronic" cough, but a careful history will reveal a shorter duration of repetitive episodes with coughs resolving completely in between infections. Chronic cough usually is defined as lasting for more than 3 to 4 weeks. Chronic cough is a symptom, not a diagnosis, and the underlying cause should be ascertained.