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 Cough in Children Cough helps clear materials from the airways and prevent them from going to the lungs. The materials may be particles that have been inhaled or substances from the lungs and/or airways. Most... read more .)
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 smokers, 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 4 weeks (acute) or 4 weeks or longer (chronic).
For acute cough, the most common causes are
Postnasal drip (drainage of secretions from the nose down the throat, or pharynx)
A flare-up of chronic obstructive pulmonary disease Chronic Obstructive Pulmonary Disease (COPD) Chronic obstructive pulmonary disease is persistent narrowing (blocking, or obstruction) of the airways occurring with emphysema, chronic obstructive bronchitis, or both disorders. Cigarette... read more (COPD)
For chronic cough, the most common causes are
Airway irritation that remains after a respiratory infection resolves (also known as post-infectious cough)
Less common causes
For acute cough, less common causes include
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 Difficulty Swallowing Some people have difficulty swallowing (dysphagia). In dysphagia, foods and/or liquids do not move normally from the throat (pharynx) to the stomach. People feel as though food or liquids become... read more . 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 Asthma Asthma is a condition in which the airways narrow—usually reversibly—in response to certain stimuli. Coughing, wheezing, and shortness of breath that occur in response to specific triggers are... read more 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.
In people with a cough, certain symptoms and characteristics are cause for concern. They include
Shortness of breath
Coughing up blood
Fever that lasts longer than about 1 week
Risk factors for tuberculosis Tuberculosis (TB) Tuberculosis is a chronic contagious infection caused by the airborne bacteria Mycobacterium tuberculosis. It usually affects the lungs. Tuberculosis is spread mainly when people breathe... read more , such as being exposed to tuberculosis, having human immunodeficiency virus (HIV) infection, or taking corticosteroids or other drugs that suppress the immune system
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 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 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 Acute Bronchitis Acute bronchitis is inflammation of the windpipe (trachea) and the airways that branch off the trachea (bronchi) caused by infection. Acute bronchitis is usually caused by a viral upper respiratory... read more , asthma Asthma Asthma is a condition in which the airways narrow—usually reversibly—in response to certain stimuli. Coughing, wheezing, and shortness of breath that occur in response to specific triggers are... read more , or other disorders. A cough that brings up blood may be caused by bronchitis, tuberculosis, or lung cancer Lung Cancer Lung cancer is the leading cause of cancer death in both men and women. About 85% of cases are related to cigarette smoking. One common symptom is a persistent cough or a change in the character... read more .
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 Computed Tomography (CT) In computed tomography (CT), which used to be called computed axial tomography (CAT), an x-ray source and x-ray detector rotate around a person. In modern scanners, the x-ray detector usually... read more (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 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 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 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
CT of the sinuses to check for sinus disorders
Placement of an acid sensor in the esophagus to check for gastroesophageal reflux disease Gastroesophageal Reflux Disease (GERD) In gastroesophageal reflux disease, stomach contents, including acid and bile, flow backward from the stomach into the esophagus, causing inflammation in the esophagus and pain in the bottom... read more
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 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 drugs 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 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. 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 drugs for depression called serotonin reuptake inhibitors Selective serotonin reuptake inhibitors (SSRIs) Agomelatine, a new type of antidepressant, is a possible treatment for major depressive episodes. Several types of drugs can be used to treat depression: Selective serotonin reuptake inhibitors... read more .
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.
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 evidence indicating effectiveness of these drugs is lacking. The most commonly used expectorants are over-the-counter preparations that contain guaifenesin.
In people with cystic fibrosis Cystic Fibrosis (CF) Cystic fibrosis is a hereditary disease that causes certain glands to produce abnormally thick secretions, resulting in tissue and organ damage, especially in the lungs and the digestive tract... read more , dornase alfa (inhaled recombinant human deoxyribonuclease I) can be used to help thin the pus-filled mucus that results from chronic respiratory infections. This drug does not seem to have an effect in people with chronic bronchitis.
Also, inhaling a saline (salt) solution or inhaling acetylcysteine (for up to a few days) sometimes helps thin excessively thick and troublesome mucus.
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 phenylephrine) that relieve a stuffy nose are only useful for relieving a cough that is caused by postnasal drip.
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.
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.
Drugs (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.