Cough is a sudden, forceful expulsion of air from the lungs. It is the fifth most common reason people see a doctor. The function of a cough is to clear material from the airways and to protect the lungs from particles that have been inhaled. People may cough on purpose (voluntarily) or spontaneously (involuntarily).

Coughs vary considerably. A cough may be dry (unproductive) or it may be productive, bringing up blood or sputum (also called phlegm). Sputum is a mixture of mucus, debris, and cells expelled by the lungs. It may be clear, yellow, green, or streaked with blood.

People who cough very hard may strain their rib muscles or cartilage, causing pain in the chest, particularly when they breathe in, move, or cough again. Cough may be very distressing and interfere with sleep. However, if coughing increases slowly over decades, as it may in smokers, people may hardly be aware of it.

Causes

Cough occurs when the airways are irritated. Likely causes of cough depend on whether the cough has lasted less than 3 weeks (acute) or 3 weeks or longer (chronic).

Common causes: For acute cough, the most common causes are

• An upper respiratory infection (URI), including acute bronchitis
• Postnasal drip (drainage of secretions from the nose down the throat, or pharynx)
• A flare-up of chronic obstructive pulmonary disease (COPD)
• Pneumonia

For chronic cough, the most common causes are

• Chronic bronchitis
• Postnasal drip
• Airway irritation that remains after a respiratory infection resolves
• Gastroesophageal reflux

Less common causes: For acute cough, less common causes include

• A blood clot in the lungs (pulmonary embolism)
• Heart failure
• A foreign object (such as a piece of food) that has been inhaled (aspirated)

However, people who accidentally inhale something typically know why they are coughing and tell their doctor unless they have dementia, stroke, or another disorder that causes difficulty communicating.

For chronic cough, less common causes include

• Use of blood pressure drugs called angiotensin-converting enzyme (ACE) inhibitors (see High Blood Pressure: Antihypertensive Drugs)
• Lung cancer
• Tuberculosis
• Fungal infections of the lungs

People who have dementia or stroke often have trouble swallowing. As a result, they may aspirate small amounts of food and drink, saliva, or stomach contents into their windpipe (trachea). These people may repeatedly aspirate small amounts of these materials without their caregiver's knowledge and may then develop a chronic cough.

Asthma may cause cough. Rarely, the main symptom of asthma is cough rather than wheezing. This type of asthma is called cough-variant asthma.

Evaluation

Not every cough requires immediate evaluation by a doctor. The following information can help people decide whether a doctor's evaluation is needed and help them know what to expect during the evaluation.

Warning signs: In people with a cough, certain symptoms and characteristics are cause for concern. They include

• Shortness of breath
• Coughing up blood
• Weight loss
• Fever that lasts longer than about 1 week
• Risk factors for tuberculosis, such as being exposed to tuberculosis, having HIV infection, or taking corticosteroids
• Risk factors for HIV infection, such as high-risk sexual activities or use of street drugs by injection

When to see a doctor: People who have warning signs should see a doctor right away unless the only warning sign is weight loss. Then, a delay of a week or so is not harmful. People who may have inhaled something should also see a doctor right away.

People with an acute cough but no warning signs can wait a few days to see whether the cough stops or becomes less severe, particularly if they also have a congested nose and sore throat, which suggest that the cause may be a URI.

People who have had a chronic cough but no warning signs should see a doctor at some point, but a delay of a week or so is unlikely to be harmful.

What the doctor does: Doctors first ask questions about the person's symptoms and medical history. Doctors then do a physical examination. What they find during the history and physical examination often suggests a cause of the cough and the tests that may need to be done (see Symptoms of Lung Disorders: Some Causes and Features of Cough).

Some obvious findings are less helpful in making a diagnosis because they can occur in several disorders that cause cough. For example, whether sputum is yellow or green or thick or thin does not help distinguish bacterial infection from other possible causes. Wheezing may occur with bronchitis, asthma, or other disorders. A cough that brings up blood may be caused by bronchitis, tuberculosis, or lung cancer.

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Some Causes and Features of Cough Cause Common Features* Tests Acute (lasting less than 3 weeks) Upper respiratory infections, including acute bronchitis A runny, congested nose with red mucosa (the tissues that line the nose) Sore throat A doctor's examination Pneumonia Fever, a feeling of illness, a cough that produces sputum (productive cough), and shortness of breath Sudden onset of sharp chest pain that worsens when taking deep breaths Certain abnormal breath sounds, heard through a stethoscope A chest x-ray For people who are seriously ill or who become ill while in the hospital, cultures of sputum and blood Postnasal drip (due to an allergy, a virus, or bacteria) Headache, sore throat, and a congested nose with pale, swollen mucosa Nausea Sometimes a drip visible at the back of the throat Usually only a doctor's examination Sometimes use of antihistamines and decongestant drugs to see whether symptoms go away A chronic obstructive pulmonary disease (COPD) flare-up Wheezing, shortness of breath, and breathing through pursed lips Cough often produces sputum In people who already have COPD A doctor's examination Sometimes a chest x-ray A foreign object† A cough that begins suddenly in people who have a disorder that interferes with communication, swallowing, or both No symptoms of an upper respiratory infection In people who otherwise are feeling well A chest x-ray Bronchoscopy Pulmonary embolism† (sudden blockage of an artery in a lung, usually by a blood clot) Sudden appearance of sharp chest pain that usually worsens when inhaling Shortness of breath A rapid heart rate and a rapid breathing rate Often risk factors for pulmonary embolism, such as cancer, immobility (as results from being bedbound), blood clots in the legs, pregnancy, use of birth control pills (oral contraceptives) or other drugs that contain estrogen, recent surgery or hospitalization, or a family history of the disorder Specialized lung imaging tests, such as CT angiography or ventilation-perfusion (V/Q) scanning (see Diagnosis of Lung Disorders: Chest Imaging) Heart failure† Shortness of breath that worsens while lying flat or that appears 1–2 hours after falling asleep Sounds suggesting fluid in the lungs, heard through a stethoscope Usually swelling (edema) in the legs A chest x-ray Sometimes a blood test to measure a substance that is produced when the heart is strained called brain natriuretic peptide (BNP) Sometimes echocardiography Chronic (lasting 3 weeks or longer) Chronic bronchitis (in smokers) A productive cough on most days of the month or for 3 months of the year for 2 successive years Frequent clearing of the throat and shortness of breath No congested nose or sore throat In people known to have COPD A chest x-ray Tests to evaluate how well the lungs are functioning (pulmonary function testing—see Diagnosis of Lung Disorders: Pulmonary Function Testing (PFT)) Postnasal drip (typically due to an allergy) Headache, sore throat, and a congested nose with pale, swollen mucosa Sometimes a drip visible at the back of the throat Sometimes only a doctor's examination Sometimes use of antihistamines and decongestants to see whether symptoms go away Sometimes allergy testing Gastroesophageal reflux Burning pain in the chest (heartburn) or abdomen that tends to worsen after eating certain foods, while exercising, or while lying flat A sour taste, particularly after awakening Hoarseness Wheezing A cough that occurs in the middle of the night or early morning Sometimes no symptoms other than cough Sometimes only a doctor's examination Sometimes use of drugs that suppress acid, such as a histamine-2 (H2) blocker or proton pump inhibitor, to see whether symptoms go away Sometimes insertion of a flexible viewing tube into the esophagus and stomach (endoscopy) Sometimes placement of a sensor in the esophagus to monitor acidity (pH) for 24 hours Asthma (cough-variant) A cough that seems to occur after various triggers, such as exposure to pollen or another allergen, cold, or exercise Possibly wheezing and shortness of breath Pulmonary function testing Sometimes use of bronchodilators (drugs that widen airways), such as albuterolSome Trade Names PROVENTIL-HFA VENTOLIN HFA , to see whether symptoms go away Airway irritation that remains after a respiratory tract infection resolves A dry, nonproductive cough that occurs immediately after a respiratory tract infection No congested nose or sore throat A chest x-ray Angiotensin-converting enzyme (ACE) inhibitors A dry, persistent cough Use of an ACE inhibitor (cough may develop within days or months after starting the drug) Stopping the ACE inhibitor to see whether symptoms go away Aspiration A wet-sounding cough after eating or drinking, visible difficulty swallowing, or both In people who have had a stroke or another disorder that causes difficulty communicating (such as dementia) A chest x-ray Sometimes x-ray tests of swallowing (modified barium pharyngography) Bronchoscopy (see Diagnosis of Lung Disorders: Bronchoscopy A lung tumor† A cough that sometimes produces blood Weight loss, fever, and night sweats Enlarged, firm, painless lymph nodes in the neck A chest x-ray Often CT of the chest Often bronchoscopy Tuberculosis or fungal infections† A cough that sometimes produces blood Weight loss, fever, and night sweats Exposure to someone with tuberculosis Residence in or travel to an area where tuberculosis or fungal lung infections are common Presence of HIV infection or risk factors for HIV infection (see Human Immunodeficiency Virus HIV Infection: Transmission of Infection) A chest x-ray Skin testing and, if positive, examination and culture of sputum Sometimes CT of the chest *Features include symptoms and results of the doctor's examination. Features mentioned are typical but not always present. †These causes are rare. CT = computed tomography. Some Causes and Features of Cough Cause Common Features* Tests Acute (lasting less than 3 weeks) Upper respiratory infections, including acute bronchitis A runny, congested nose with red mucosa (the tissues that line the nose) Sore throat A doctor's examination Pneumonia Fever, a feeling of illness, a cough that produces sputum (productive cough), and shortness of breath Sudden onset of sharp chest pain that worsens when taking deep breaths Certain abnormal breath sounds, heard through a stethoscope A chest x-ray For people who are seriously ill or who become ill while in the hospital, cultures of sputum and blood Postnasal drip (due to an allergy, a virus, or bacteria) Headache, sore throat, and a congested nose with pale, swollen mucosa Nausea Sometimes a drip visible at the back of the throat Usually only a doctor's examination Sometimes use of antihistamines and decongestant drugs to see whether symptoms go away A chronic obstructive pulmonary disease (COPD) flare-up Wheezing, shortness of breath, and breathing through pursed lips Cough often produces sputum In people who already have COPD A doctor's examination Sometimes a chest x-ray A foreign object† A cough that begins suddenly in people who have a disorder that interferes with communication, swallowing, or both No symptoms of an upper respiratory infection In people who otherwise are feeling well A chest x-ray Bronchoscopy Pulmonary embolism† (sudden blockage of an artery in a lung, usually by a blood clot) Sudden appearance of sharp chest pain that usually worsens when inhaling Shortness of breath A rapid heart rate and a rapid breathing rate Often risk factors for pulmonary embolism, such as cancer, immobility (as results from being bedbound), blood clots in the legs, pregnancy, use of birth control pills (oral contraceptives) or other drugs that contain estrogen, recent surgery or hospitalization, or a family history of the disorder Specialized lung imaging tests, such as CT angiography or ventilation-perfusion (V/Q) scanning (see Diagnosis of Lung Disorders: Chest Imaging) Heart failure† Shortness of breath that worsens while lying flat or that appears 1–2 hours after falling asleep Sounds suggesting fluid in the lungs, heard through a stethoscope Usually swelling (edema) in the legs A chest x-ray Sometimes a blood test to measure a substance that is produced when the heart is strained called brain natriuretic peptide (BNP) Sometimes echocardiography Chronic (lasting 3 weeks or longer) Chronic bronchitis (in smokers) A productive cough on most days of the month or for 3 months of the year for 2 successive years Frequent clearing of the throat and shortness of breath No congested nose or sore throat In people known to have COPD A chest x-ray Tests to evaluate how well the lungs are functioning (pulmonary function testing—see Diagnosis of Lung Disorders: Pulmonary Function Testing (PFT)) Postnasal drip (typically due to an allergy) Headache, sore throat, and a congested nose with pale, swollen mucosa Sometimes a drip visible at the back of the throat Sometimes only a doctor's examination Sometimes use of antihistamines and decongestants to see whether symptoms go away Sometimes allergy testing Gastroesophageal reflux Burning pain in the chest (heartburn) or abdomen that tends to worsen after eating certain foods, while exercising, or while lying flat A sour taste, particularly after awakening Hoarseness Wheezing A cough that occurs in the middle of the night or early morning Sometimes no symptoms other than cough Sometimes only a doctor's examination Sometimes use of drugs that suppress acid, such as a histamine-2 (H2) blocker or proton pump inhibitor, to see whether symptoms go away Sometimes insertion of a flexible viewing tube into the esophagus and stomach (endoscopy) Sometimes placement of a sensor in the esophagus to monitor acidity (pH) for 24 hours Asthma (cough-variant) A cough that seems to occur after various triggers, such as exposure to pollen or another allergen, cold, or exercise Possibly wheezing and shortness of breath Pulmonary function testing Sometimes use of bronchodilators (drugs that widen airways), such as albuterolSome Trade Names PROVENTIL-HFA VENTOLIN HFA , to see whether symptoms go away Airway irritation that remains after a respiratory tract infection resolves A dry, nonproductive cough that occurs immediately after a respiratory tract infection No congested nose or sore throat A chest x-ray Angiotensin-converting enzyme (ACE) inhibitors A dry, persistent cough Use of an ACE inhibitor (cough may develop within days or months after starting the drug) Stopping the ACE inhibitor to see whether symptoms go away Aspiration A wet-sounding cough after eating or drinking, visible difficulty swallowing, or both In people who have had a stroke or another disorder that causes difficulty communicating (such as dementia) A chest x-ray Sometimes x-ray tests of swallowing (modified barium pharyngography) Bronchoscopy (see Diagnosis of Lung Disorders: Bronchoscopy A lung tumor† A cough that sometimes produces blood Weight loss, fever, and night sweats Enlarged, firm, painless lymph nodes in the neck A chest x-ray Often CT of the chest Often bronchoscopy Tuberculosis or fungal infections† A cough that sometimes produces blood Weight loss, fever, and night sweats Exposure to someone with tuberculosis Residence in or travel to an area where tuberculosis or fungal lung infections are common Presence of HIV infection or risk factors for HIV infection (see Human Immunodeficiency Virus HIV Infection: Transmission of Infection) A chest x-ray Skin testing and, if positive, examination and culture of sputum Sometimes CT of the chest *Features include symptoms and results of the doctor's examination. Features mentioned are typical but not always present. †These causes are rare. CT = computed tomography.

Testing: The need for tests depends on what doctors find during the history and physical examination, particularly whether warning signs are present.

If people have any warning signs, tests usually include

• Measurement of oxygen levels in the blood with a sensor placed on a finger (pulse oximetry)
• A chest x-ray

Skin tests, chest x-ray, and sometimes computed tomography (CT) of the chest for tuberculosis and blood tests for HIV infection are also done if people have lost weight or have risk factors for these disorders.

If no warning signs are present, doctors can often make a diagnosis based on the history and physical examination and begin treatment without doing tests. In some people, the examination suggests a diagnosis, but tests are done to confirm it (see Symptoms of Lung Disorders: Some Causes and Features of Cough).

If the examination does not suggest a cause of a cough and no warning signs are present, many doctors try giving people a drug to treat one of two common causes of cough:

• An antihistamine/decongestant combination or a nasal corticosteroid spray (for postnasal drip)
• A proton pump inhibitor or histamine-2 (H₂) blocker (for gastroesophageal reflux disease)

If these drugs relieve cough, further testing is usually unnecessary. If cough is not relieved, doctors typically do tests in the following order until a test suggests a diagnosis:

• A chest x-ray
• Pulmonary function tests to check for asthma
• CT of the sinuses to check for sinus disorders
• Placement of an acid sensor in the esophagus to check for gastroesophageal reflux disease

If people have a chronic cough, doctors usually do a chest x-ray. If the cough produces blood, doctors typically send a sputum sample to the laboratory. There, technicians try to grow bacteria in the sample (sputum culture) and use a microscope to check the sample for cancer cells (cytology). Often, if doctors suspect lung cancer (for example, in middle-aged or older people who have smoked for a long time and who have lost weight or have other general symptoms), they also do CT of the chest and sometimes bronchoscopy.

Treatment

The best way to treat cough is to treat the underlying disorder. For example, antibiotics can be used for pneumonia, and inhalers containing drugs that widen airways (bronchodilators) or corticosteroids can be used for COPD or asthma. Generally, because coughing plays an important role in bringing up sputum and clearing the airways, a cough should not be suppressed. However, if the cough is severe, interferes with sleep, or has certain causes, various treatments may be tried.

There are two basic approaches to people who are coughing:

• Cough suppressants (antitussive therapy), which reduce the urge to cough
• Expectorants, which are meant to thin the mucus blocking the airways to the lungs and make mucus easier to cough up (but evidence of effectiveness is lacking)

Cough suppressants: Cough suppressants include the following.

All opioids suppress cough because they reduce the responsiveness of the cough center in the brain. Codeine is the opioid used most often for cough. Codeine and other opioid cough suppressants may cause nausea, vomiting, and constipation and may be addictive. They can also cause drowsiness, particularly when a person is taking other drugs that reduce concentration (such as alcohol, sedatives, sleep aids, antidepressants, or certain antihistamines). Thus, opioids are not always safe, and doctors usually reserve them for special situations, such as cough that persists despite other treatments and that interferes with sleep.

Dextromethorphan is related to codeine but is technically not an opioid. It also suppresses the cough center in the brain. DextromethorphanSome Trade Names
DELSYM
is the active ingredient in many over-the-counter (OTC) and prescription cough preparations. It is not addictive and, when used correctly, causes little drowsiness. However, it is frequently abused by people, particularly adolescents, because in high doses, it causes euphoria. Overdose causes hallucinations, agitation, and sometimes coma. Overdose is particularly dangerous for people who are taking drugs for depression called serotonin reuptake inhibitors (see Mood Disorders: Drug Therapy).

Benzonatate is a local anesthetic taken by mouth. It numbs receptors in the lungs that respond to stretching and thus makes the lungs less sensitive to irritation that triggers cough.

Certain people, especially those who are coughing up a large amount of sputum, should limit their use of drugs that suppress cough.

Expectorants: Some doctors recommend expectorants (sometimes called mucolytics) to help loosen mucus by making bronchial secretions thinner and easier to cough up. Expectorants do not suppress a cough, and the effectiveness of these drugs is lacking. The most commonly used expectorants are OTC preparations that contain guaifenesinSome Trade Names
MUCINEX
. Doctors may prescribe a saturated solution of potassium iodideSome Trade Names
THYROSAFE
to loosen mucus. A small dose of syrup of ipecac may help children, especially those who have croup.

In people with cystic fibrosis, dornase alfaSome Trade Names
PULMOZYME
(inhaled recombinant human deoxyribonuclease I) can be used to help thin the pus-filled mucus that results from chronic respiratory infections.

Also, inhaling a saline (salt) solution or inhaling acetylcysteineSome Trade Names
ACETADOTE
(for up to a few days) sometimes helps thin excessively thick and troublesome mucus.

Other drugs: Antihistamines, which dry the respiratory tract, have little or no value in treating a cough, except when it is caused by an allergy involving the nose, throat, and windpipe. When coughs have 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 for relieving a cough that is caused by postnasal drip.

Other treatments: Steam inhalation (for example, using a vaporizer) is commonly thought to reduce cough. Other topical treatments, such as cough drops, are also popular, but there is no convincing evidence that these other treatments are effective.

Key Points

• Most coughs are caused by minor respiratory infections or postnasal drip.
• Warning signs in people with a cough include shortness of breath, coughing up blood, weight loss, and fever that lasts longer than about 1 week.
• Doctors can usually make a diagnosis based on results of the medical history and physical examination.
• Drugs (cough suppressants and expectorants) should be used to treat cough only they are when appropriate—cough suppressants only when cough is severe, expectorants only when thick mucus is difficult to cough up, or either type when a doctor recommends it.

Last full review/revision July 2012 by Noah Lechtzin, MD, MHS