A cough is a defensive reflex of the body that functions to keep the airways clear of irritating or obstructing substances so that breathing and the intake of oxygen is effective. A cough is a symptom of a wide variety of mild to serious diseases, disorders and conditions. A cough can result from infection, inflammation, trauma, malignancy, airway obstruction and other abnormal processes.
A cough can occur in any age group or population. A cough can indicate a mild condition, such as briefly inhaling campfire smoke. A cough can also be the result of a moderate condition, disorder or disease, such as influenza, upper respiratory infection or adenoid disorder. A cough can also accompany serious conditions that can even be life-threatening. These include pneumonia acute bronchitis, bronchiolitis, asthma, choking, and congestive heart failure.

Depending on the cause, a cough can be short-term and disappear quickly, such as when a cough occurs after briefly inhaling second-hand smoke. A cough can also occur in sudden, severe episodes, such as a cough that happens with whooping cough. A cough can also be chronic and ongoing over a long period of time, such as when a cough is due to smoking or lung cancer.