Cough is an explosive expiratory maneuver that is reflexively or deliberately intended to clear the airways. It is one of the most common symptoms prompting physician visits. (See also Cough in Children Cough in Children Cough is a reflex that helps clear the airways of secretions, protects the airway from foreign body aspiration, and can be the manifesting symptom of a disease. Cough is one of the most common... read more .)
Likely causes of cough (see table Some Causes of Cough Some Causes of Cough 
) differ depending on whether the symptom is acute (present < 4 weeks) or chronic (1 General reference Cough is an explosive expiratory maneuver that is reflexively or deliberately intended to clear the airways. It is one of the most common symptoms prompting physician visits. (See also Cough... read more ).
In acute cough, the most common causes are
Upper respiratory infection (URI Common Cold The common cold is an acute, usually afebrile, self-limited viral infection causing upper respiratory symptoms, such as rhinorrhea, cough, and sore throat. Diagnosis is clinical. Handwashing... read more ), including acute bronchitis
Postnasal drip
In chronic cough, the most common causes are
Postnasal drip
Airway hyperresponsiveness after resolution of a viral or bacterial respiratory infection (ie, postinfection cough)
COPD Chronic Obstructive Pulmonary Disease (COPD) Chronic obstructive pulmonary disease (COPD) is airflow limitation caused by an inflammatory response to inhaled toxins, often cigarette smoke. Alpha-1 antitrypsin deficiency and various occupational... read more
(chronic obstructive pulmonary disease)
The causes of cough in children Cough in Children Cough is a reflex that helps clear the airways of secretions, protects the airway from foreign body aspiration, and can be the manifesting symptom of a disease. Cough is one of the most common... read more are similar to those in adults, but asthma Wheezing and Asthma in Infants and Young Children Wheezing is a relatively high-pitched whistling noise produced by movement of air through narrowed or compressed small airways. It is common in the first few years of life and is typically caused... read more and foreign body aspiration may be more common in children.
Very rarely, impacted cerumen or a foreign body in the external auditory canal triggers reflex cough through stimulation of the auricular branch of the vagus nerve. Psychogenic cough is even rarer and is a diagnosis of exclusion.
Patients with chronic cough may develop a secondary reflex or psychogenic component to their cough. Also, protracted coughing may injure the bronchial mucosa, which may trigger more coughing.
General reference
1. Morice AH, Millqvist E, Bieksiene K, et al: ERS guidelines on the diagnosis and treatment of chronic cough in adults and children. Eur Respir J 55(1): 1901136, 2020. doi: 10.1183/13993003.01136-2019
Evaluation of Cough
History
History of present illness should cover the duration and characteristics of the cough (eg, whether dry or productive of sputum or blood, and whether it is accompanied by dyspnea, chest pain, or both). Asking about precipitating factors (eg, cold air, strong odors) and the timing of the cough (eg, primarily at night) can be revealing.
Review of systems should seek symptoms of possible cause, including runny nose and sore throat (upper respiratory infection [ URI Common Cold The common cold is an acute, usually afebrile, self-limited viral infection causing upper respiratory symptoms, such as rhinorrhea, cough, and sore throat. Diagnosis is clinical. Handwashing... read more ], postnasal drip); fever, chills, and pleuritic chest pain (pneumonia Overview of Pneumonia Pneumonia is acute inflammation of the lungs caused by infection. Initial diagnosis is usually based on chest x-ray and clinical findings. Causes, symptoms, treatment, preventive measures, and... read more ); night sweats and weight loss (tumor Lung Carcinoma Lung carcinoma is the leading cause of cancer-related death in men and women worldwide. About 85% of cases are related to cigarette smoking. Symptoms can include cough, chest discomfort or pain... read more 
, tuberculosis [ TB Tuberculosis (TB) Tuberculosis is a chronic, progressive mycobacterial infection, often with an asymptomatic latent period following initial infection. Tuberculosis most commonly affects the lungs. Symptoms include... read more 
]); heartburn (gastroesophageal reflux Gastroesophageal Reflux Disease (GERD) Incompetence of the lower esophageal sphincter allows reflux of gastric contents into the esophagus, causing burning pain. Prolonged reflux may lead to esophagitis, stricture, and rarely metaplasia... read more 
); and difficulty swallowing or choking episodes while eating or drinking (aspiration).
Past medical history should note recent respiratory infections (ie, within previous 1 to 2 months); history of allergies Allergic Rhinitis Allergic rhinitis is seasonal or perennial itching, sneezing, rhinorrhea, nasal congestion, and sometimes conjunctivitis, caused by exposure to pollens or other allergens. Diagnosis is by history... read more , asthma Asthma Asthma is a disease of diffuse airway inflammation caused by a variety of triggering stimuli resulting in partially or completely reversible bronchoconstriction. Symptoms and signs include dyspnea... read more , COPD Chronic Obstructive Pulmonary Disease (COPD) Chronic obstructive pulmonary disease (COPD) is airflow limitation caused by an inflammatory response to inhaled toxins, often cigarette smoke. Alpha-1 antitrypsin deficiency and various occupational... read more (chronic obstructive pulmonary disease), and gastroesophageal reflux disease Gastroesophageal Reflux Disease (GERD) Incompetence of the lower esophageal sphincter allows reflux of gastric contents into the esophagus, causing burning pain. Prolonged reflux may lead to esophagitis, stricture, and rarely metaplasia... read more ; risk factors for (or known) TB Tuberculosis (TB) Tuberculosis is a chronic, progressive mycobacterial infection, often with an asymptomatic latent period following initial infection. Tuberculosis most commonly affects the lungs. Symptoms include... read more or HIV infection Human Immunodeficiency Virus (HIV) Infection Human immunodeficiency virus (HIV) infection results from 1 of 2 similar retroviruses (HIV-1 and HIV-2) that destroy CD4+ lymphocytes and impair cell-mediated immunity, increasing risk of certain... read more 
; and smoking history. Drug history should specifically include use of angiotensin-converting enzyme (ACE) inhibitors. Patients with chronic cough should be asked about exposure to potential respiratory irritants or allergens and travel to or residence in regions with endemic fungal illness.
Physical examination
Vital signs should be reviewed for the presence of tachypnea and fever.
General examination should look for signs of respiratory distress and chronic illness (eg, wasting, lethargy).
Examination of the nose and throat should focus on appearance of the nasal mucosa (eg, color, congestion) and presence of discharge (external or in posterior pharynx). Ears should be examined for foreign bodies, masses, or signs of infection.
The cervical and supraclavicular areas should be inspected and palpated for lymphadenopathy.
A full lung examination is done, particularly including adequacy of air entry and exit; symmetry of breath sounds; and presence of crackles, wheezes, or both. Signs of consolidation (eg, egophony, dullness to percussion) should be sought.
Red flags
The following findings are of particular concern:
Dyspnea
Hemoptysis
Weight loss
Persistent fever
Risk factors for TB or HIV infection
Interpretation of findings
Some findings point to particular diagnoses (1 Evaluation reference Cough is an explosive expiratory maneuver that is reflexively or deliberately intended to clear the airways. It is one of the most common symptoms prompting physician visits. (See also Cough... read more —see table Some Causes of Cough Some Causes of Cough ).
Other important findings are less specific. For example, the color (eg, yellow, green) and thickness of sputum do not help differentiate bacterial from other causes. Wheezing Wheezing Wheezing is a relatively high-pitched whistling noise produced by movement of air through narrowed or compressed small airways. It is a symptom as well as a physical finding. Prolonged expiratory... read more may occur with several causes. Hemoptysis Hemoptysis Hemoptysis is coughing up of blood from the respiratory tract. Massive hemoptysis is production of ≥ 600 mL of blood (about a full kidney basin’s worth) within 24 hours. Most of the lung’s blood... read more in small amounts may occur with severe cough of many etiologies, although larger amounts of hemoptysis suggest bronchitis, bronchiectasis, TB, or primary lung cancer. Fever, night sweats, and weight loss may occur with many chronic infections as well as with cancer.
Testing
Pulse oximetry and chest x-ray should be done in patients with red flag findings of dyspnea or hemoptysis and patients in whom suspicion of pneumonia is high. A chest x-ray and testing for TB and HIV infection should be done in patients with weight loss or risk factors for those infections.
For many patients without red flag findings, clinicians can base the diagnosis on history and physical examination findings and begin treatment without testing. For patients without a clear cause but no red flag findings, many clinicians empirically begin treatment for postnasal drip (eg, antihistamine and decongestant combinations, nasal corticosteroid sprays, or nasal muscarinic antagonist sprays), airway hyperreactivity (eg, inhaled corticosteroid or short-acting beta-adrenergic agonist), or gastroesophageal reflux disease (eg, proton pump inhibitors, H2 blockers). An adequate response to these interventions usually precludes the need for further evaluation.
A chest x-ray should be done in patients with chronic cough in whom presumptive treatment is ineffective. If the x-ray findings are unremarkable, many clinicians sequentially test for asthma (pulmonary function tests with methacholine challenge if standard spirometry is normal), sinus disease (sinus CT), and gastroesophageal reflux disease (esophageal pH monitoring).
Sputum culture is helpful for patients with a possible indolent infection, such as pertussis, TB, or nontuberculous mycobacterial infection.
Chest CT and possibly bronchoscopy should be done in patients in whom lung cancer or another bronchial tumor is suspected (eg, patients with a long smoking history, nonspecific constitutional signs) and in patients in whom empiric therapy has failed and who have inconclusive findings on preliminary testing.
Evaluation reference
1. Morice AH, Millqvist E, Bieksiene K, et al: ERS guidelines on the diagnosis and treatment of chronic cough in adults and children. Eur Respir J 55(1): 1901136, 2020. doi: 10.1183/13993003.01136-2019
Treatment of Cough
Treatment is management of the cause (1 Treatment reference Cough is an explosive expiratory maneuver that is reflexively or deliberately intended to clear the airways. It is one of the most common symptoms prompting physician visits. (See also Cough... read more ).
There is little evidence to support the use of cough suppressants or mucolytic agents. Coughing is an important mechanism for clearing secretions from the airways and can assist in recovery from respiratory infections. Therefore, although patients often expect or request cough suppressants, such treatment should be given with caution and reserved for patients with a URI and for patients receiving therapy for the underlying disorder for whom cough is still troubling. Cough suppressants may help some patients with chronic cough who have a reflex or psychogenic component to their cough or who develop bronchial mucosal injury.
Antitussives depress the medullary cough center (dextromethorphan and codeine) or anesthetize stretch receptors of vagal afferent fibers in bronchi and alveoli (benzonatate). Dextromethorphan, a congener of the opioid levorphanol, is effective as a tablet or syrup at a dose of 15 to 30 mg orally 1 to 4 times a day for adults or 0.25 mg/kg orally 4 times a day for children. Codeine has antitussive, analgesic, and sedative effects, but dependence is a potential problem, and nausea, vomiting, constipation, and tolerance are common adverse effects. Usual doses are 10 to 20 mg orally every 4 to 6 hours as needed for adults and 0.25 to 0.5 mg/kg orally 4 times a day for children. Other opioids (hydrocodone, hydromorphone, methadone, morphine) have antitussive properties but are avoided because of high potential for dependence and abuse. Benzonatate, a congener of tetracaine that is available in liquid-filled capsules, is effective at a dose of 100 to 200 mg orally 3 times a day.
Expectorants are thought to decrease viscosity and facilitate expectoration (coughing up) of secretions but are of limited, if any, benefit in most circumstances. Guaifenesin (200 to 400 mg orally every 4 hours in syrup or tablet form) is most commonly used because it has no serious adverse effects, but multiple expectorants exist, including bromhexine, ipecac, and saturated solution of potassium iodide (SSKI). Aerosolized expectorants such as N-acetylcysteine, DNase, and hypertonic saline are generally reserved for hospital-based treatment of cough in patients with bronchiectasis or cystic fibrosis. Ensuring adequate hydration may facilitate expectoration, as may inhalation of steam, although neither technique has been rigorously tested.
Topical treatments, such as acacia, licorice, glycerin, honey, and wild cherry cough drops or syrups (demulcents), are locally and perhaps emotionally soothing, but their use is not supported by scientific evidence.
Protussives, which stimulate cough, are indicated for such disorders as cystic fibrosis and bronchiectasis, in which a productive cough is thought to be important for airway clearance and preservation of pulmonary function. DNase or hypertonic saline is given in conjunction with chest physical therapy and postural drainage to promote cough and expectoration. This approach is beneficial in cystic fibrosis but not in most other causes of chronic cough.
Bronchodilators, such as albuterol and ipratropium or inhaled corticosteroids, can be effective for cough after URI and in cough-variant asthma.
Treatment reference
1. Morice AH, Millqvist E, Bieksiene K, et al: ERS guidelines on the diagnosis and treatment of chronic cough in adults and children. Eur Respir J 55(1): 1901136, 2020. doi: 10.1183/13993003.01136-2019
Key Points
Danger signs include respiratory distress, chronic fever, weight loss, and hemoptysis.
Clinical diagnosis is usually adequate.
Occult gastroesophageal reflux disease should be remembered as a possible cause.
Antitussives and expectorants should be used selectively.
