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.
While people can generally cough on purpose, a cough is usually a reflex triggered when an irritant stimulates one or more of the cough receptors found atdifferent 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 thevocal cords at the upper part of the larynx (glottis) shuts, trapping the airin the lungs. As the diaphragm and other muscles involved in breathing pressagainst the lungs, the glottis suddenly opens, producing an explosive outflow of air at speeds greater than 100 mi (160 km) per hour.
In normal situations, most people cough once or twice an hour during the dayto clear the airway of irritants. However, when the level of irritants in theair is high or when the respiratory system becomes infected, coughing may become frequent and prolonged. It may interfere with exercise or sleep, and itmay also cause distress if accompanied by dizziness, chest pain, or breathlessness. In the majority of cases, frequent coughing lasts one to two weeks andtapers off as the irritant or infection subsides. If a cough lasts more thanthree weeks it is considered a chronic cough, and physicians will try to determine a cause beyond an acute infection or irritant.
Coughs are generally described as either dry or productive. A dry cough doesnot bring up a mixture of mucus, irritants, and other substances from the lungs (sputum), whereas a productive cough does. In the case of a bacterial infection, the sputum brought up in a productive cough may be greenish, gray, orbrown. 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.
Coughs are usually caused by respiratory infections, including 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 cryptococcoses.
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 removed it by coughing. Postnasal 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 also be a side effect of beta-blockers and ACE inhibitors, which are drugs used for treating high blood pressure.
To determine the cause of a cough, a physician should take an exact medical history and perform an exam. The appearance of the sputum will also help determine what type of infection, if any, may be involved. The doctor may even observe the sputum microscopically for the presence of bacteria and white bloodcells. Chest x rays may help indicate the presence and extent of such infections as pneumonia or tuberculosis. If these actions are not enough to determine the cause of the cough, a bronchoscopy or laryngoscopy may be ordered. These tests use slender tubular instruments to inspect the interior of the bronchi and larynx.
Treatment of a cough generally involves addressing the condition causing it.An acute infection such as pneumonia may require antibiotics, an asthma-induced cough may be treated with the use of bronchodialators, or an antihistaminemay be administered in the case of an allergy. Physicians prefer not to suppress a productive cough, since it aids the body in clearing respiratory system of infective agents and irritants. However, cough medicines may be given ifthe patient cannot rest because of the cough or if the cough is not productive, as is the case with most coughs associated with colds or flu. The two types of drugs used to treat coughs are antitussives, which suppress a cough, and expectorants, which make mucus easier to cough up by thinning it. Some studies have shown that in acute infections, simply increasing fluid intake has the same thinning effect as taking expectorants.
Many health practitioners advise increasing fluids and breathing in warm, humidified air as ways of loosening chest congestion. Others recommend hot tea flavored with honey as a temporary home remedy for coughs caused by colds or flu. Various vitamins, such as vitamin C, may be helpful in preventing or treating conditions (including colds and flu) that lead to coughs. Avoiding mucus-producing foods can be effective in healing a cough condition. These mucus-producing foods can vary, based on individual intolerance, but dairy productsare a major mucus-producing food for most people.
Because the majority of coughs are related to the common cold or influenza, most will end in 7-21 days. The outcome of coughs due to a more serious underlying disease depends on the nature of that disease. It is important to identify and treat the underlying disease and origin of the cough.