• Merck Manual
• >
• Patients & Caregivers
• >
• Lung and Airway Disorders
• >
• Symptoms of Lung Disorders
4

A cough is a sudden, explosive exhalation of air; the function of a cough is to clear material from the airways.

Coughing, a familiar but complicated reflex, is one way in which the lungs and airways are protected. Along with other mechanisms, coughing helps to protect the lungs from particles that have been inhaled. Coughing sometimes brings up sputum (also called phlegm)—a mixture of mucus, debris, and cells expelled by the lungs.

Causes

Coughing occurs when the airways are irritated. Respiratory infections—usually bacterial or viral—irritate the airways and are a common cause of coughing. Allergies can irritate the airways as well. People who smoke often cough. Smoke not only irritates the airways but also damages the cells that line the airways, including the hairlike projections that normally cleanse the airways of debris (cilia). Coughing may also result from postnasal drip, in which nasal secretions drain down the back of the nose into the throat and sometimes into the trachea and other airways, where they produce irritation. Coughing may result from gastroesophageal reflux, in which stomach or esophageal contents flow backward from the esophagus into the trachea and airways, producing irritation. Another cause of cough can be drugs, for example, angiotensin-converting enzyme (ACE) inhibitors (see High Blood Pressure: Antihypertensive Drugs). Narrowing of the airways below the windpipe (bronchoconstriction), foreign bodies, or tumors in the airway can cause cough, wheezing, or both. Bronchoconstriction occurs in asthma, in chronic obstructive pulmonary disease, and heart failure (when fluid accumulates in the lungs).

Coughs vary considerably. A cough may be distressing, especially if coughing episodes are accompanied by chest pain, shortness of breath, blood, or unusually large amounts of or very sticky sputum. However, if coughing increases slowly over decades, as it may in a smoker, the person may hardly be aware of it.

Evaluation

Information about a cough helps a doctor determine its cause. Therefore, a doctor may ask:

• How long has the cough been present?
• At what time of day does the cough occur?
• What factors—such as cold air, body position, talking, eating, or drinking—influence the cough?
• Is the cough accompanied by chest pain, shortness of breath, hoarseness, dizziness, or wheezing?
• Does the cough bring up sputum or blood?
• Are there symptoms of another disorder that could cause a cough (for example, gastroesophageal reflux or postnasal drip)?
• Could a drug be causing the cough?
• What color is the sputum?

The appearance of the sputum, especially a change in color or consistency, occasionally helps the doctor identify the cause. A yellowish, greenish, or brownish appearance may indicate a bacterial infection. Clear but very sticky (mucoid) sputum is characteristic of asthma. Occasionally, a doctor may use a microscope to examine a sputum sample. Bacteria and white blood cells are additional indications of infection. The presence of a specific type of white blood cell (eosinophil) suggests asthma. A cough may also produce blood, which commonly suggests bronchitis but may also suggest more serious disorders. Usually, a chest x-ray or other tests are done when a person develops a cough that is severe or persistent or has no obvious cause.

Treatment

Because coughing plays an important role in bringing up sputum and clearing the airways, a cough should not be suppressed unless it interferes with sleep. Treating an underlying disorder—such as an infection, fluid in the lungs, or asthma—is more important. For example, antibiotics can be given for an infection, or inhalers can be used for asthma. Depending on the severity of the cough and its cause, a variety of drugs may be used for treatment. When cough results from narrowing of the airways, bronchodilators may provide relief. It is not clear how well other drugs relieve cough.

Antitussive Therapy: Antitussive drugs are given to suppress cough. All opioids are antitussives because they suppress the cough center in the brain. Codeine is the opioid used most often for cough. Codeine may cause nausea, vomiting, and constipation; it may also be addictive. If codeine is taken for a prolonged period, the dose needed to suppress a cough may need to be increased. Opioid cough suppressants can cause drowsiness, particularly when the person also is taking other drugs that reduce concentration (such as alcohol, sedatives, sleep aids, antidepressants, and certain antihistamines). Opioids are not always safe, and doctors usually reserve them for special situations.

Several non-opioid cough suppressants, such as dextromethorphanSome Trade Names
DELSYM
and benzonatateSome Trade Names
TESSALON
, are antitussives that also suppress the cough center in the brain. These drugs, and others, are the active ingredients in many over-the-counter and prescription cough medications. They are not addictive and, when used correctly, produce little drowsiness. In certain people, especially those who are coughing up an abundant amount of sputum, frequent use of these cough suppressants is not recommended.

Steam inhalation, for example from a vaporizer, can help stop a cough by reducing irritation in the throat (pharynx) and airways. The moisture from the steam also loosens secretions, making them easier to cough up. A cool-mist humidifier can achieve the same result. Some doctors believe that drinking sufficient water can produce good hydration and is as effective as steam inhalation for loosening secretions.

Expectorants: Some doctors recommend expectorants (sometimes called mucolytics) to help loosen mucus by making bronchial secretions thinner and easier to cough up, although these drugs do not suppress a cough. It is not clear how effective these drugs are. A saturated solution of potassium iodideSome Trade Names
THYROSAFE
may be prescribed. The most commonly used over-the-counter preparations contain guaifenesinSome Trade Names
MUCINEX
or terpin hydrate. A small dose of syrup of ipecac may help in children, especially in those who have croup.

In cystic fibrosis, dornase alfaSome Trade Names
PULMOZYME
(inhaled recombinant human deoxyribonuclease I) is used to help thin the pus-filled mucus that results from chronic respiratory infections. Also, inhalation of a saline (salt) solution or use of acetylcysteineSome Trade Names
ACETADOTE
(for up to a few days) sometimes helps thin excessively thick and troublesome mucus.

Bronchodilators, Corticosteroids, Antihistamines, and Decongestants: Bronchodilators, such as inhaled albuterolSome Trade Names
PROVENTIL-HFA VENTOLIN HFA
and similar drugs, and inhaled corticosteroids are effective if a cough occurs as a result of airway narrowing (bronchoconstriction), as happens in asthma and chronic obstructive pulmonary disease. TheophyllineSome Trade Names
THEOLAIR
, which is taken by mouth, is sometimes helpful. Some people who develop wheezing or prolonged cough after viral respiratory infections appear to benefit from short-term use of bronchodilators.

Antihistamines, which dry the respiratory tract, have little or no value in treating a cough, except when it is caused by an upper airway allergy. With coughs from other causes, such as bronchitis, the drying action of antihistamines can be harmful, thickening respiratory secretions and making them difficult to cough up.

Decongestants such as phenylephrineSome Trade Names
PROMETH VC PLAIN
that relieve a stuffy nose are only useful in relieving a cough that is caused by postnasal drip.

Last full review/revision November 2006 by James H. Fisher, MD