Coughing is a short, intense exhalation of air from the lungs caused by the rapid contraction of the chest muscles and diaphragm. Although it is possible to cough voluntarily, most coughing is involuntary. Coughing is the usual response of the body to the presence of foreign material, irritating gases or excess mucus in the airways leading to the lungs. It is a common symptom of allergies, the common cold, bronchitis, tuberculosis and several other diseases. As such, coughing alone is not an important diagnostic tool.
Although coughing is a normal body function, too much coughing can irritate the airways, cause hemorrhaging of the air passages, make it difficult for the patient to breath, and interrupt rest and sleep. In many cases, patients are given narcotics or other depressants, which suppress the reflex that leads to the cough.
What the patient "coughs up" can be a diagnostic tool. For example, a dry cough usually indicates that the lungs are being irritated by the inhalation of noxious gases or small particles. Coughing up mucous is an indication that the patient may have an infection in their lungs, indicating antibiotics are required to stave off the possibility of pneumonia. Coughing up blood is a serious symptom, indicating that the patient has inhaled a corrosive substance or has a condition that is destroying lung tissue.