Cough is a strong, sudden expelling of air from the lungs. Coughing serves as a body defense that helps rid the lungs of harmful substances, such as pus or blood. But coughing also spreads germs that cause disease.
A person coughs if the lining of the respiratory tract becomes irritated. Certain nerves respond to this irritation, causing the individual to take a deep breath. These nerves also cause the trachea (windpipe) to close partially. The diaphragm, a large muscle that lies under the lungs, contracts rapidly, pushing air out of the lungs. The trachea then opens and the air rushes through the breathing passages and out of the mouth. The air carries along any substance in its path.
Irritants that produce coughing include smoking, air pollution, and respiratory infections. The irritation may lead to inflammation and cause the layer of mucus in the throat to thicken. Some cough medicines help reduce inflammation and loosen mucus so it can be coughed up easily. Others lessen the activity of certain nerves that produce coughing.
Mucus coughed up from the lungs helps physicians diagnose certain diseases. Doctors examine mucus under a microscope for evidence of bacteria, cancer cells, or other indication of disease.
