In clinical guidelines chronic cough is defined as a cough lasting more than 8 weeks in adults and more than 4 weeks in children. Some consensus statements suggest that a chronic cough must persist upwards of three months or more to be considered chronic. The prevalence of chronic cough is about 10% although the prevalence may differ depending on definition and geographic area. Chronic cough is a common symptom in several different respiratory diseases like

COPD Chronic obstructive pulmonary disease (COPD) is a type of progressive lung disease characterized by chronic respiratory symptoms and airflow limitation. GOLD defines COPD as a heterogeneous lung condition characterized by chronic respiratory s ...

pulmonary fibrosis Pulmonary fibrosis is a condition in which the lungs become scarred over time. Symptoms include shortness of breath, a dry cough, feeling tired, weight loss, and nail clubbing. Complications may include pulmonary hypertension, respiratory ...

but in non-smokers with a normal chest x-ray chronic cough are often associated with

asthma Asthma is a common long-term inflammatory disease of the airways of the lungs. It is characterized by variable and recurring symptoms, reversible airflow obstruction, and easily triggered bronchospasms. Symptoms include episodes of wh ...

, rhinosinusitis, and

gastroesophageal reflux disease Gastroesophageal reflux disease (GERD) or gastro-oesophageal reflux disease (GORD) is a chronic upper gastrointestinal disease in which stomach content persistently and regularly flows up into the esophagus, resulting in symptoms and/or ...

or could have no specific cause known ( idiopathic). Generally, a cough, for example after an upper respiratory tract infection, lasts around one to two weeks; however, chronic cough can persist for an extended period of time, several years in some cases. The current theory about the cause of chronic cough, independent of associated condition, is that it is caused by a hypersensitivity in the cough sensory nerves, called cough hypersensitivity syndrome. There are a number of treatments available, depending on the associated disease but the clinical management of the patients remains a challenge. Risk factors include exposure to cigarette smoke, and exposure to

pollution Pollution is the introduction of contaminants into the natural environment that cause harm. Pollution can take the form of any substance (solid, liquid, or gas) or energy (such as radioactivity, heat, sound, or light). Pollutants, the component ...

, especially

particulates Particulate matter (PM) or particulates are microscopic particles of solid or liquid matter suspension (chemistry), suspended in the atmosphere of Earth, air. An ''aerosol'' is a mixture of particulates and air, as opposed to the particulate ...

Signs and symptoms

Common symptoms present in chronic cough is allotussia, a cough triggered by innocuous stimuli such as perfumes or talking and hypertussia, an increased sensitivity to known tussive triggers like smoke or fumes. Laryngeal

paraesthesia Paresthesia is a sensation of the skin that may feel like numbness (''hypoesthesia''), tingling, pricking, chilling, or burning. It can be temporary or chronic and has many possible underlying causes. Paresthesia is usually painless and can oc ...

, irritation, tickle or lump in the throat, is also common. Other symptoms includes frequent throat clearing and sore throat, hoarseness, wheezing or shortness of breath. If the chronic cough is associated with rhinosinusitis or reflux, symptoms may also include a runny or stuffy nose, a feeling of liquid running down the back of the throat ( postnasal drip),

heartburn Heartburn is a burning sensation felt behind the breastbone. It is a symptom that is commonly linked to acid reflux and is often triggered by food, particularly fatty, sugary, spicy, chocolate, citrus, onion-based and tomato-based products. Ly ...

or sour taste in a person's mouth, and in rare cases coughing blood. Most patients with chronic cough have hypersensitivity of the

cough reflex The cough reflex occurs when stimulation of cough receptors in the respiratory tract by dust or other foreign particles produces a cough, which causes rapidly moving air which usually remove the foreign material before it reaches the lungs. This ...

, such as the Arnold's nerve reflex.

Complications

Long-term coughing and constant irritation of the

upper airway The respiratory tract is the subdivision of the respiratory system involved with the process of conducting air to the alveoli for the purposes of gas exchange in mammals. The respiratory tract is lined with respiratory epithelium as respiratory ...

can be problematic for individuals who have chronic cough. Due to the consistent coughing, this can interfere with an individual's daily life. This interference can thus cause additional problems such as affecting a person's ability to ensure a consistent sleep, daytime fatigue, difficulty concentrating at work or school, headache, and dizziness. Other more severe but rare complications include fainting,

urinary incontinence Urinary incontinence (UI), also known as involuntary urination, is any uncontrolled leakage of urine. It is a common and distressing problem, which may have a significant effect on quality of life. Urinary incontinence is common in older women ...

, and broken ribs, caused by excessive coughing.

Causes

Possible causes, alone or in conjunction, that produce the chronic cough include the following. * Postnasal drip, when excess mucus is produced in the sinus of the nose and drips back towards the throat, causes a cough reflex, also known as upper airway cough syndrome. Postnasal drip coughing can be caused by the direct irritation of the postnasal drip or by inflammation of cough receptors in the upper airway. Postnasal drip cases contribute 34% of chronic cough cases. *

Asthma Asthma is a common long-term inflammatory disease of the airways of the lungs. It is characterized by variable and recurring symptoms, reversible airflow obstruction, and easily triggered bronchospasms. Symptoms include episodes of wh ...

that affects the upper respiratory tract. Other causes such as cold air or breathing in chemicals can also induce coughing. *

Gastroesophageal reflux disease Gastroesophageal reflux disease (GERD) or gastro-oesophageal reflux disease (GORD) is a chronic upper gastrointestinal disease in which stomach content persistently and regularly flows up into the esophagus, resulting in symptoms and/or ...

(GERD), a common condition where the backflow of stomach acid between the throat and the stomach causes irritation, can lead to chronic cough. *

Infections An infection is the invasion of tissue (biology), tissues by pathogens, their multiplication, and the reaction of host (biology), host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmis ...

such as

pneumonia Pneumonia is an Inflammation, inflammatory condition of the lung primarily affecting the small air sacs known as Pulmonary alveolus, alveoli. Symptoms typically include some combination of Cough#Classification, productive or dry cough, ches ...

flu Influenza, commonly known as the flu, is an infectious disease caused by influenza viruses. Symptoms range from mild to severe and often include fever, runny nose, sore throat, muscle pain, headache, coughing, and fatigue. These sympto ...

common cold The common cold, or the cold, is a virus, viral infectious disease of the upper respiratory tract that primarily affects the Respiratory epithelium, respiratory mucosa of the human nose, nose, throat, Paranasal sinuses, sinuses, and larynx. ...

tuberculosis Tuberculosis (TB), also known colloquially as the "white death", or historically as consumption, is a contagious disease usually caused by ''Mycobacterium tuberculosis'' (MTB) bacteria. Tuberculosis generally affects the lungs, but it can al ...

or other infections in the upper respiratory tract often include coughing that can persist even after the infection has subsided. Chronic cough is commonly mistaken as a symptom of the infection known as

whooping cough Whooping cough ( or ), also known as pertussis or the 100-day cough, is a highly contagious, Vaccine-preventable diseases, vaccine-preventable Pathogenic bacteria, bacterial disease. Initial symptoms are usually similar to those of the common c ...

. * Blood pressure drugs such as

angiotensin-converting enzyme Angiotensin-converting enzyme (), or ACE, is a central component of the renin–angiotensin system (RAS), which controls blood pressure by regulating the volume of fluids in the body. It converts the hormone angiotensin I to the active vasocon ...

, which is commonly prescribed to individuals with high blood pressure and cardiac failure, are known to have a side effect of chronic cough. *

Chronic bronchitis Bronchitis is inflammation of the bronchi (large and medium-sized airways) in the lungs that causes coughing. Bronchitis usually begins as an infection in the nose, ears, throat, or sinuses. The infection then makes its way down to the bronchi. ...

, an inflammation in the major airways such as the

bronchial A bronchus ( ; : bronchi, ) is a passage or airway in the lower respiratory tract that conducts Atmosphere of Earth, air into the lungs. The first or primary bronchi to branch from the trachea at the Carina of trachea, carina are the right main b ...

tubules, causes the coughing of coloured

sputum Sputum is mucus that is coughed up from the lower airways (the trachea and bronchi). In medicine, sputum samples are usually used for a naked-eye examination, microbiological investigation of respiratory infections, and Cytopathology, cytological ...

. Most carriers of chronic bronchitis have a history of smoking. Chronic bronchitis is on a spectrum of smoking-related lung disease also known as

chronic obstructive pulmonary disease Chronic obstructive pulmonary disease (COPD) is a type of progressive lung disease characterized by chronic respiratory symptoms and airflow limitation. GOLD defines COPD as a heterogeneous lung condition characterized by chronic respiratory s ...

(COPD). Other lung diseases on the spectrum such as

emphysema Emphysema is any air-filled enlargement in the body's tissues. Most commonly emphysema refers to the permanent enlargement of air spaces (alveoli) in the lungs, and is also known as pulmonary emphysema. Emphysema is a lower respiratory tract di ...

can co-exist with COPD. It accounts for 5% of chronic cough. * Chemical irritants, such as

cigarette A cigarette is a narrow cylinder containing a combustible material, typically tobacco, that is rolled into Rolling paper, thin paper for smoking. The cigarette is ignited at one end, causing it to smolder; the resulting smoke is orally inhale ...

smoke, are a common factor that can lead to chronic cough. These irritants typically contribute towards chronic bronchitis. * Other notable rare causes include aspiration,

bronchiectasis Bronchiectasis is a disease in which there is permanent enlargement of parts of the bronchi, airways of the lung. Symptoms typically include a chronic cough with sputum, mucus production. Other symptoms include shortness of breath, hemoptysis, co ...

bronchiolitis Bronchiolitis is inflammation of the small airways also known as the bronchioles in the lungs. Acute bronchiolitis is caused by a viral infection, usually affecting children younger than two years of age. Symptoms may include fever, cough, run ...

cystic fibrosis Cystic fibrosis (CF) is a genetic disorder inherited in an autosomal recessive manner that impairs the normal clearance of Sputum, mucus from the lungs, which facilitates the colonization and infection of the lungs by bacteria, notably ''Staphy ...

laryngopharyngeal reflux Laryngopharyngeal reflux (LPR) or laryngopharyngeal reflux disease (LPRD) is the retrograde flow of gastric contents into the larynx, oropharynx and/or the nasopharynx. LPR causes respiratory symptoms such as cough and wheezing and is often asso ...

lung cancer Lung cancer, also known as lung carcinoma, is a malignant tumor that begins in the lung. Lung cancer is caused by genetic damage to the DNA of cells in the airways, often caused by cigarette smoking or inhaling damaging chemicals. Damaged ...

, non-asthmatic eosinophilic bronchitis,

sarcoidosis Sarcoidosis (; also known as Besnier–Boeck–Schaumann disease) is a disease involving abnormal collections of White blood cell, inflammatory cells that form lumps known as granulomata. The disease usually begins in the lungs, skin, or lymph n ...

Risk factors

Life style related factors, some health conditions or diseases, and environmental exposures can put people at risk for developing a chronic cough. Life-style risk factors include smoking cigarettes that the individual smokes themselves or breathes from second-hand exposure. Long-term exposure to smoke can irritate airways and lead to chronic cough and in severe cases lung damage. Other risk factors include exposure to polluted air. Individuals who work in factories or laboratories that deal with

chemicals A chemical substance is a unique form of matter with constant chemical composition and characteristic properties. Chemical substances may take the form of a single element or chemical compounds. If two or more chemical substances can be combin ...

have a chance of developing chronic cough from long-term exposure.

Mechanism

Coughing A cough is a sudden expulsion of air through the large breathing passages which 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 ...

is a mechanism of the body that is essential to the normal physiological function of clearing the throat, which involves a

reflex In biology, a reflex, or reflex action, is an involuntary, unplanned sequence or action and nearly instantaneous response to a stimulus. Reflexes are found with varying levels of complexity in organisms with a nervous system. A reflex occurs ...

of the afferent sensory limb, central processing centre of the

brain The brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head (cephalization), usually near organs for ...

, and the efferent limb. With the body components involved,

sensory receptor Sensory neurons, also known as afferent neurons, are neurons in the nervous system, that convert a specific type of stimulus, via their receptors, into action potentials or graded receptor potentials. This process is called sensory transduc ...

s are also used. These receptors include

rapidly adapting receptor A mechanoreceptor, also called mechanoceptor, is a sensory receptor that responds to mechanical pressure or distortion. Mechanoreceptors are located on sensory neurons that convert mechanical pressure into electrical signals that, in animals, ar ...

s which respond to mechanical stimuli, slowly adapting receptors, and

nociceptor A nociceptor (; ) is a sensory neuron that responds to damaging or potentially damaging stimuli by sending "possible threat" signals to the spinal cord and the brain. The brain creates the sensation of pain to direct attention to the body part, ...

s which respond to chemical stimuli such as hormones in the body. To start the reflex, the afferent impulses are transmitted to the medulla of the brain; this stimulus is then interpreted. The efferent impulses are then triggered by the medulla, causing the signal to travel down the

larynx The larynx (), commonly called the voice box, is an organ (anatomy), organ in the top of the neck involved in breathing, producing sound and protecting the trachea against food aspiration. The opening of larynx into pharynx known as the laryngeal ...

and

bronchial tree A bronchus ( ; : bronchi, ) is a passage or airway in the lower respiratory tract that conducts air into the lungs. The first or primary bronchi to branch from the trachea at the carina are the right main bronchus and the left main bronchus. Thes ...

. This then triggers a cascade of events that involve the

intercostal muscles The intercostal muscles comprise many different groups of muscles that run between the ribs, and help form and move the chest wall. The intercostal muscles are mainly involved in the mechanical aspect of breathing by helping expand and shrink th ...

abdominal wall In anatomy, the abdominal wall represents the boundaries of the abdominal cavity. The abdominal wall is split into the anterolateral and posterior walls. There is a common set of layers covering and forming all the walls: the deepest being the vi ...

, diaphragm and

pelvic floor The pelvic floor or pelvic diaphragm is an anatomical location in the human body which has an important role in urinary and anal continence, sexual function, and support of the pelvic organs. The pelvic floor includes muscles, both skeletal and ...

, which together create the reflex known as coughing.

Diagnosis

There are three main types of chronic cough. * Upper airway cough syndrome is the most common cause of chronic coughing. It is diagnosed when the secretion of excess mucus from the nose or sinus drains into the

pharynx The pharynx (: pharynges) is the part of the throat behind the human mouth, mouth and nasal cavity, and above the esophagus and trachea (the tubes going down to the stomach and the lungs respectively). It is found in vertebrates and invertebrates ...

or the back of the throat, causing an induced cough. *

is a main way to produce the chronic cough. This is due to the airflow being obstructed when coughing, causing a shortness of breath, wheezing,

dyspnea Shortness of breath (SOB), known as dyspnea (in AmE) or dyspnoea (in BrE), is an uncomfortable feeling of not being able to breathe well enough. The American Thoracic Society defines it as "a subjective experience of breathing discomfort that ...

and coughing. * Gastroesophageal reflux disease (GERD) is identified with two mechanisms, which are the distal esophageal acid stimulating the esophageal-treachebronchial cough reflex due to the vagus nerve, and the microbial esophageal contents of the pharynx and tracheobronchial causing a cough reflex.

Imaging

X-rays An X-ray (also known in many languages as Röntgen radiation) is a form of high-energy electromagnetic radiation with a wavelength shorter than those of ultraviolet rays and longer than those of gamma rays. Roughly, X-rays have a wavelength ran ...

are used to check for lung cancer, pneumonia and other lung diseases that are contributing to the chronic cough. X-rays of the sinus also can provide evidence of an infection in the area. *

CT scans A computed tomography scan (CT scan), formerly called computed axial tomography scan (CAT scan), is a medical imaging technique used to obtain detailed internal images of the body. The personnel that perform CT scans are called radiographers or ...

are used to check the condition of the patient's lungs and to check sinus cavities for infections. * Lung Function Test, a simple test in which the patient inhales and exhales into a

spirometer A spirometer is an apparatus for measuring the volume of air inspired and expired by the lungs. A spirometer measures ventilation, the movement of air into and out of the lungs. The spirogram will identify two different types of abnormal ventilat ...

, is normally used to diagnose asthma or chronic obstructive pulmonary disease. * With lab tests, a sample of the patient's mucus is tested for bacteria * Scope tests are used if the above tests are not able to diagnose the chronic cough. A special test may be used that involves a thin, flexible tube which contains a light and camera. This is inserted within the patient through the respiratory tract. A bronchoscope is used for seeing the lungs and air passages, and a

biopsy A biopsy is a medical test commonly performed by a surgeon, interventional radiologist, an interventional radiologist, or an interventional cardiology, interventional cardiologist. The process involves the extraction of sampling (medicine), sample ...

of the linings of the airway may be taken. Additionally, a rhinoscope can be used to examine the upper airway tract. * Children are typically diagnosed with chest X-rays or spirometry Typical evaluation of chronic cough begins with diagnosing the person's lifestyle choices, such as smoking, environmental exposure or medication. From this doctors can opt to use chest radiography if the patient does not smoke, takes any angiotensin-converting enzyme inhibitor, or still has a persistent cough after the period of medication.

Concerning findings

A prolonged cough such as one that falls under the chronic cough syndrome can become a medical emergency. Concerning symptoms are a high fever, coughing of blood, chest pain, difficulty of breathing, appetite loss, excess mucus being coughed, fatigue, night sweats, and unexplained weight loss.

Types

By diagnosing which type of

cough A cough is a sudden expulsion of air through the large breathing passages which can help clear them of fluids, irritants, foreign particles and Microorganism, microbes. As a protective reflex, coughing can be repetitive with the cough reflex fol ...

is present, individuals may further identify the cause of the chronic cough. These coughing types include the following. A dry cough is a persistent cough where no

mucus Mucus (, ) is a slippery aqueous secretion produced by, and covering, mucous membranes. It is typically produced from cells found in mucous glands, although it may also originate from mixed glands, which contain both Serous fluid, serous and muc ...

is present; this can be a sign of an infection. A chronic wet cough is a cough where excess mucus is present; depending on the colour of the phlegm, bacterial infections may be present. A stress cough is when the airways of the throat are blocked to the point that it causes a reflexive spasm. A whooping cough is when a ‘whooping’ sound is present; this is a normally an indication of infection.

Treatment

* Upper airway cough syndrome treatments include avoiding environmental irritants (chemicals) and offending antigens. This may involve treating the sinus with antibiotics to stop nasal drip. Individuals should avoid decongestants found in off-the-shelf pharmacies, to allow rhinitis medicaments to work. In severe cases where the cause is not clear, patients should use empirical therapy, which is a combination of antihistamine and decongestants. Results typically show within two weeks of therapy, but it can take up to several months for results to show. Absence of the standard clinical procedure that tests for rhinorrhea and excess sputum production should not preclude an empirical trial with antihistamine and decongestants, as they are not effective in treating upper airway cough syndrome. * Treating children who have a non-specific chronic cough with asthma medications such as inhaled beta2-agonists (e.g.,

salbutamol Salbutamol, also known as albuterol and sold under the brand name Ventolin among others, is a medication that opens up the medium and large airways in the lungs. It is a short-acting β2 adrenergic receptor agonist that causes relaxation of ...

) or inhaled corticosteroids does not improve the clinical symptoms. *

Codeine Codeine is an opiate and prodrug of morphine mainly used to treat pain, coughing, and diarrhea. It is also commonly used as a recreational drug. It is found naturally in the sap of the opium poppy, ''Papaver somniferum''. It is typically use ...

-based cough medications are contraindicated for children under 12 years old due to the risk of respiratory suppression and the potential for opioid toxicity. *

Leukotriene receptor antagonist An antileukotriene, also known as leukotriene modifier and leukotriene receptor antagonist, is a medication which functions as a leukotriene-related enzyme inhibitor ( arachidonate 5-lipoxygenase) or leukotriene receptor antagonist ( cysteinyl leu ...

-based medications and methylxanthines are not recommended for treating children with persistent non-specific cough. * Gastroesophageal reflux disease (

GERD Gastroesophageal reflux disease (GERD) or gastro-oesophageal reflux disease (GORD) is a chronic upper gastrointestinal disease in which stomach content persistently and regularly flows up into the esophagus, resulting in symptoms and/or ...

) treatments can include intense monitoring with a dual channel 24-hour pH probe for diagnosis of the severity of GERD. Other monitors such as nasopharyngoscopy can reveal glottis changes associated with the refluxes that occur. Acid suppressive medications can be taken, which include histamine 2 (H2) blockers, proton pump inhibitors (PPI) and prokinetic agents. This medication tends to show results within two weeks; however six to eight weeks is ideal for conclusive results. Patients can remain on treatment for up to six months. * Moderate levels of evidence suggest that the use of a

clinical pathway A clinical pathway, also known as care pathway, integrated care pathway, critical pathway, or care map, is one of the main tools used to manage the quality in healthcare concerning the standardisation of care processes. It has been shown that th ...

that includes an evidence-based algorithm (flow chart) for treating children who have chronic cough may improve clinical outcomes. There is insufficient evidence to determine if the following approaches are beneficial for treating chronic cough: Treating childhood obstructive sleep apnoea, modifying the indoor air quality, or treatment with inhaled

chromones Chromone (or 1,4-benzopyrone) is a derivative of benzopyran 4H-1-Benzopyran is an organic compound with the formula . It is one of two isomers of benzopyran, the other being 2H-1-Benzopyran, 2H-1-benzopyran, which is more prevalent. It can be ...

Epidemiology

The prevalence of chronic cough in many communities in Europe and the U.S. is 9–33% of the population. Chronic cough is three times more common in those who smoke compared to people who never smoke. The most important risk factors for chronic cough are tobacco smoking and working in a dusty job. Exposure to

tobacco Tobacco is the common name of several plants in the genus '' Nicotiana'' of the family Solanaceae, and the general term for any product prepared from the cured leaves of these plants. More than 70 species of tobacco are known, but the ...

smoke in a home environment is also a risk factor for children due to

second-hand smoke Passive smoking is the inhalation of tobacco smoke, called passive smoke, secondhand smoke (SHS) or environmental tobacco smoke (ETS), by individuals other than the active smoker. It occurs when tobacco smoke diffuses into the surrounding atm ...

inhalation. Other causes of chronic cough include higher

particulate matter Particulate matter (PM) or particulates are microscopic particles of solid or liquid matter suspended in the air. An ''aerosol'' is a mixture of particulates and air, as opposed to the particulate matter alone, though it is sometimes defin ...

concentrations in air, related to increase cough and sore throat in children. An increase in

nitrogen dioxide Nitrogen dioxide is a chemical compound with the formula . One of several nitrogen oxides, nitrogen dioxide is a reddish-brown gas. It is a paramagnetic, bent molecule with C2v point group symmetry. Industrially, is an intermediate in the s ...

has also shown a rising association with chronic cough syndrome.

Children

A cough that is four weeks or longer in duration is considered chronic for children. Most common causes for children include asthma, respiratory tract infections and GERD. An estimation of between one and 21% of children suffer from chronic cough. Causes typically diagnosed include viral bronchitis, post-infectious cough, cough-variant asthma, upper airway cough syndrome, psychogenic cough and GERD. Due to some diagnostic methods being invasive, typically children are not suitable for such diagnosis under the age of 15. However, the bare minimum tests include chest radiography and spirometry.

References

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