A cough is a sudden, forceful expulsion of air from the lungs, often triggered by irritation in the throat or airways. It serves as a protective reflex to clear mucus, foreign particles, or irritants. Coughs can be classified as dry or productive, with productive coughs bringing up mucus. Coughing can be caused by various factors, including infections like common cold or flu, allergies, or environmental irritants such as smoke. While most coughs are temporary and resolve on their own, persistent coughs may require medical attention to identify underlying conditions.