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 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.
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.
Antitussive —A drug used to suppress coughing.
Expectorant —A drug that promotes the discharge of mucus from respiratory system.
Gastroesophageal reflux —The backflow of stomach contents into the esophagus.
Glottis —The opening between the vocal cords at the upper part of the larynx.
Larynx —Also known as the voice box, the larynx is the part of the airway that lies between the pharynx and the trachea. It is composed of cartilage that contains the apparatus for voice production–the vocal cords and the muscles and ligaments that move the cords.
Sputum —The substance that is coughed up from the lungs and spit out through the mouth. It is usually a mixture of saliva and mucus, but may contain blood or pus in patients with lung abscess or other diseases of the lungs.
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.
To determine the cause of a cough, a physician should take an exact medical history and perform an exam. Information regarding the duration of the cough, what other symptoms may accompany it, and what environmental factors may influence it aid the doctor in his or her diagnosis. The appearance of the sputum also helps 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 blood cells. 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 bronchodilators, or an antihistamine may 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 if the person 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 and expectorants .
Antitussives are drugs that suppress a cough. Narcotics—primarily codeine—are used as antitussives and work by depressing the cough center in the brain. However, they can cause such side effects as drowsiness, nausea , and constipation . Dextromethorphan, the primary ingredient in many over-the-counter cough remedies, also depresses the brain's cough center but without the side effects associated with narcotics. Demulcents relieve coughing by coating irritated passageways.
Expectorants are drugs that thin mucus in order to make it easier to cough up. Guaifenesin and terpin hydrate are the primary ingredients in most over-the-counter expectorants. However, some studies have shown that in acute infections, simply increasing fluid intake has the same thinning effect as taking expectorants.
Coughs due to bacterial or viral upper respiratory infections may be effectively treated with botanical and homeopathic therapies. The choice of remedy will vary and be specific to the type of cough the person has. Some combination over-the-counter herbal and homeopathic cough formulas can be very effective for cough relief. Lingering coughs or coughing up blood should be treated by a trained practitioner.
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, or minerals , such as zinc, may be helpful in preventing or treating conditions (including colds and flu) that lead to coughs. Avoiding of mucus-producing foods can be effective in healing a cough condition. These mucus-producing foods can vary, based on individual intolerance, but dairy products are 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 seven to 21 days. The outcome of coughs due to a more serious underlying disease depends on the pathology of that disease.
It is important to identify and treat the underlying disease and origin of the cough. It is helpful to avoid cigarette smoke and coming in direct contact with people experiencing cold or flu symptoms. Hands should be washed frequently during episodes of upper-respiratory illnesses.
Persons with coughs should be sure to maintain balanced and healthy diets.
Parents of children under the age of five should closely monitor their children when they have a cough. Parents of children over five years of age must accept the fact that their children are likely to acquire coughs and related illnesses from schoolmates. They should remain vigilant and consider having their children seen by a physician if the cough does not resolve after five to seven days.
See also Common cold .
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American Academy of Family Physicians. 11400 Tomahawk Creek Parkway, Leawood, KS 66211–2672. Web site: http://www.aafp.org/.
American Academy of Pediatrics. 141 Northwest Point Blvd., Elk Grove Village, IL 60007–1098. Web site: http://www.aap.org/default.htm.
American College of Physicians. 190 N Independence Mall West, Philadelphia, PA 19106–1572. Web site: http://www.acponline.org/.
American Lung Association. 1740 Broadway, New York, NY 10019. Web site: http://www.lungusa.org.
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L. Fleming Fallon, Jr., MD, DrPH