Cough Health Article

Definition

A cough is a forceful release of air from the lungs that can be heard. Coughing protects the respiratory system by clearing it of irritants and secretions.

Description

While people can generally cough voluntarily, a true cough is usually a reflex triggered when an irritant stimulates one or more of the cough receptors found at different points in the respiratory system. These receptors then send a message to the cough center in the brain, which in turn tells the body to cough. A cough begins with a deep breath in, at which point the opening between the vocal cords at the upper part of the larynx (glottis) shuts, trapping the air in the lungs. As the diaphragm and other muscles involved in breathing press against the lungs, the glottis suddenly opens, producing an explosive outflow of air at speeds greater than 100 miles (160 km) per hour.

In normal situations, most people cough once or twice an hour during the day to clear the airway of irritants. However, when the level of irritants in the air is high or when the respiratory system becomes infected, coughing may become frequent and prolonged. It may interfere with exercise or sleep, and it may also cause distress if accompanied by dizziness, chest pain, or breathlessness. In the majority of cases, frequent coughing lasts one to two weeks and tapers off as the irritant or infection subsides. If a cough lasts more than three weeks it is considered a chronic cough, and physicians try to determine a cause beyond an acute infection or irritant.

Coughs are generally described as either dry or productive. A dry cough does not bring up a mixture of mucus, irritants, and other substances from the lungs (sputum), while a productive cough does. In the case of a bacterial infection, the sputum brought up in a productive cough may be greenish, gray, or brown. In the case of an allergy or viral infection it may be clear or white. In the most serious conditions, the sputum may contain blood.

Demographics

Formal statistics on coughs are not maintained. Virtually all persons will experience coughs several times each year throughout their lives.

Causes and symptoms

In the majority of cases, coughs are caused by respiratory infections, including the following:

• colds or influenza, the most common causes of coughs
• bronchitis, an inflammation of the mucous membranes of the bronchial tubes
• croup, a viral inflammation of the larynx, windpipe, and bronchial passages that produces a bark-like cough in children
• whooping cough, a bacterial infection accompanied by the high-pitched cough for which it is named
• pneumonia, a potentially serious bacterial infection that produces discolored or bloody mucus
• tuberculosis, another serious bacterial infection that produces bloody sputum
• fungal infections, such as aspergillosis, histoplasmosis, and cryptococcosis

Environmental pollutants, such as cigarette smoke, dust, or smog, can also cause a cough. In the case of cigarette smokers, the nicotine present in the smoke paralyzes the hairs (cilia) that regularly flush mucus from the respiratory system. The mucus then builds up, forcing the body to remove it by coughing. Post-nasal drip, the irritating trickle of mucus from the nasal passages into the throat caused by allergies or sinusitis, can also result in a cough. Some chronic conditions, such as asthma, chronic bronchitis, emphysema, and cystic fibrosis, are characterized in part by a cough. A condition in which stomach acid backs up into the esophagus (gastroesophageal reflux) can cause coughing, especially when a person is lying down. A cough can also be a side-effect of medications that are administered via an inhaler. It can be a side-effect of beta-blockers and ACE inhibitors, which are drugs used for treating high blood pressure.

When to call the doctor

A physician or other healthcare provider should be called when a cough does not subside after three or four days. Individuals such as smokers, who have chronic coughs, should consult a doctor if the nature of their cough changes or they produce blood when they cough.