Cough is a sudden, forceful expulsion of air from the lungs. It is one of the most common reasons 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). (See also Cough in Children.)
Coughs vary considerably. A cough may be characterized as dry (unproductive) or 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 people who smoke, people may hardly be aware of it.
Causes of Cough
Cough occurs when the airways are irritated. Likely causes of cough depend on whether the cough has lasted less than 8 weeks (acute) or 8 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)
For chronic cough, the most common causes are
Postnasal drip
Airway irritation that remains after a respiratory infection resolves (also known as post-infectious cough)
Use of angiotensin-converting enzyme (ACE) inhibitors, which are blood pressure medications
Less common causes
For acute cough, less common causes include
A blood clot in the lungs (pulmonary embolism)
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 with memory, cognition, or communication.
For chronic cough, less common causes include
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 of Cough
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 human immunodeficiency virus (HIV) infection, or taking corticosteroids or other medications that suppress the immune system
Risk factors for HIV infection, such as high-risk sexual activities or use of illicit 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 an upper respiratory infection (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 need to be done (see table 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.
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, and examination and culture of a sputum sample 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 table 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 medication to treat one of three common causes of cough:
An antihistamine/decongestant combination or a nasal corticosteroid or nasal muscarinic antagonist spray (for postnasal drip)
A proton pump inhibitor or histamine-2 (H2) blocker (for gastroesophageal reflux disease)
An inhaled corticosteroid or short-acting beta-2-agonist bronchodilator (for asthma)
If these medications 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 adults 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 of Cough
The best way to treat cough is to treat the underlying disorder. For example, antibiotics can be used for pneumonia, and inhalers containing medications that widen airways (bronchodilators) or corticosteroids can be used for chronic obstructive pulmonary disease (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:
Opioids
All opioidsCodeine 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.
is related to codeine but is technically not an opioid. It also suppresses the cough center in the brain. Dextromethorphan 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 medications for depression called serotonin reuptake inhibitors.
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 medications that suppress cough.
Expectorants
In people with cystic fibrosis
Other medications
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.
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, fever that lasts longer than about 1 week, and risk factors for HIV infection or tuberculosis.
Doctors can usually make a diagnosis based on results of the medical history and physical examination.
Medications (cough suppressants and expectorants) should be used to treat cough only when appropriate—for example, a cough suppressant only when cough is severe or when a doctor recommends it.
