A cough is a sudden expulsion of air through the large breathing passages that can help clear them of fluids, irritants, foreign particles, and microbes. As a protective reflex, coughing can be repetitive with the cough reflex following three phases: an inhalation, a forced exhalation against a closed glottis, and a violent release of air from the lungs following the opening of the glottis, usually accompanied by a distinctive sound. Frequent coughing usually indicates the presence of a disease. Many viruses and bacteria benefit, from an evolutionary perspective, by causing the host to cough, which helps to spread the disease to new hosts. Most of the time, irregular coughing is caused by a respiratory tract infection but can also be triggered by choking, smoking, air pollution, asthma, gastroesophageal reflux disease (GERD), post-nasal drip, chronic bronchitis, lung tumors, heart failure, and medications such as angiotensin-converting-enzyme inhibitors (ACE inhibitors).
A cough is a protective reflex in healthy individuals which is influenced by psychological factors. The cough reflex is initiated by stimulation of two different classes of afferent nerves, namely the myelinated rapidly adapting receptors, and nonmyelinated C-fibers with endings in the lung. Cough is the most common reason for visiting a primary care physician in the United States. Because coughing can spread disease through infectious aerosol droplets, it is recommended to cover one's mouth and nose with the forearm, the inside of the elbow, a tissue, or a handkerchief while coughing.
Cough can be classified by its duration, character, quality, and timing. The duration can be either acute (of sudden onset) if it is present less than three weeks, sub-acute if it is present between three or eight weeks, and chronic when lasting longer than eight weeks. A cough can be non-productive (dry) or productive (when phlegm is produced that may be coughed up as sputum). It may occur only at night (then called nocturnal cough), during both night and day, or just during the day.
The type of cough may help in the diagnosis. For instance, an inspiratory "whooping" sound on coughing almost doubles the likelihood that the illness is pertussis. Blood may occur in small amounts with severe cough of many causes, but larger amounts suggest bronchitis, bronchiectasis, tuberculosis, or primary lung cancer. A number of characteristic coughs exist. While these have not been found to be diagnostically useful in adults, they are of use in children. A barky cough is part of the common presentation of croup. A staccato cough has been classically described with neonatal chlamydial pneumonia.
The complications of coughing can be classified as either acute or chronic. Acute complications include cough syncope (fainting spells due to decreased blood flow to the brain when coughs are prolonged and forceful), insomnia, cough-induced vomiting, sub conjunctiva hemorrhage, or "red-eye", coughing defecation and in women with a prolapsed uterus, cough urination. Chronic complications are common and include abdominal or pelvic hernias, fatigue fractures of lower ribs, and costochondritis.
Key issues in the history include triggers for the onset of cough, determinants of increased or decreased cough, and sputum production. Symptoms of nasopharyngeal disease should be assessed, including postnasal drip, sneezing, and rhinorrhea. GERD may be suggested by heartburn, hoarseness, sore throat, and frequent eructation. Cough-variant asthma (without other asthmatic symptoms) is suggested by noting the relationship of cough onset to asthmatic triggers.
On physical examination, signs of cardiopulmonary diseases should be assessed, including adventitious lung sounds and digital clubbing. Examination of the nasal passages, posterior pharyngeal wall, auditory canals, and tympanic membranes should be performed.
Laboratory evaluation should include chest radiography. Spirometry with bronchodilator testing can assess for reversible airflow obstruction. With normal Spirometry, methacholine challenge testing can be used to assess for asthma. Purulent sputum should be sent for routine bacterial and possibly mycobacterial cultures. Sputum cytology can reveal malignant cells in lung cancer and eosinophil in eosinophilic bronchitis. Chest CT should be considered in patients with normal chest radiographs who fail to improve with treatment.
The treatment of a cough in children is based on the underlying cause. In children, half of cases go away without treatment in 10 days and 90% in 25 days. According to the American Academy of Pediatrics, the use of cough medicine to relieve cough symptoms is supported by little evidence and thus not recommended for treating cough symptoms in children. There is tentative evidence that the use of honey is better than no treatment or diphenhydramine in decreasing coughing. It does not alleviate coughing to the same extent as dextromethorphan but it shortens the cough duration better than placebo and salbutamol. A trial of antibiotics or inhaled corticosteroids may be tried in children with a chronic cough in an attempt to treat protracted bacterial bronchitis or asthma respectively. There is insufficient evidence to recommend treating children who have a cough that is not related to a specific condition with an inhaled anticholinergic. In patient with chronic cough and a normal chest x-ray, empiric treatment is directed at the most likely cause based on the history and physical examination. If treatment directed at one empiric cause fails, empiric treatment of an alternative etiology can be considered. Cough-variant asthma is treated with inhaled glucocorticoids and as-needed inhaled β agonists. Patients on ACE inhibitors should be given a 1-month trial of discontinuing this medication. Chronic eosinophilic bronchitis often improves with inhaled glucocorticoid treatment. Symptomatic treatment of cough can include narcotics such as codeine; however, somnolence, constipation, and addiction can result. Dextromethorphan and benzonatate have fewer side effects but reduced efficacy.