Cough

Updated 26 February 2018

What is a cough?

Coughing is a normal reflex reaction due to stimulation of the cough receptors. However, coughing can be a symptom of a number of problems.

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Everyone coughs from time to time. It’s a vital defence mechanism that clears unwanted material from your lungs, and so it isn’t necessarily a sign of active or approaching illness. It can be merely a once-off effort of the body to clear the air passages. 

Coughs can last a few days, such as with a common cold, or be a more chronic cough that could last for months in some instances. A cough, interestingly, was the most common reason why patients went to see a primary care doctor in a recent study conducted in South Africa. 

The causes of coughing are varied and many. It can also be a symptom of many different conditions, not always directly related to a lung disease. There are cough receptors located in the respiratory tract, in the oesophagus, the diaphragm and the stomach. 

A cough is described as an "explosive expiratory manoeuvre that’s reflexively or deliberately intended to clear the airways". It’s aimed at clearing the throat and the air passage of inhaled irritants, such as dust or dirt particles, and excess secretions, such as mucus. A cough can also be caused by capsaicin-like compounds, such as those found in chillies.

Certain chemicals, such as swimming-pool chlorine, are highly irritating to the airways and can also make some people cough.

There are three steps in generating the cough (together, they form the cough reflex):

1. To start a cough, air needs to be inhaled into the lungs with the glottis (the vocal cords and the opening between them) open.

2. Then, there is a build-up of pressure in the lungs as the chest wall, diaphragm and stomach muscles contract with the glottis closed. 

3. When the glottis opens, there’s an explosive release of air, with speeds up to 80km/h, expelling harmful substances from the respiratory tract. (A sneeze is a much more “violent” reaction with a faster and bigger spray of particles being generated.) If a cough becomes persistent, it’s best to have a doctor examine you to determine the cause.

How common is coughing / who suffers from it?

Chronic cough is estimated to affect 7.9% to 9.6% of the global adult population. In a primary-care study, conducted in four South African provinces, nearly 20,000 consultations were evaluated.

Over 5,000 consultations were for a respiratory complaint, of which nearly 3,000 consultations were for a cough. This equates to 9% of all GP-type visits.

The reason for coughing can be wide ranging: from a self-limiting viral illness, which will go away on its own without treatment, right through to a life-threatening condition such as lung cancer. 

Local healthcare systems are well established to investigate coughs as a result of infectious diseases (e.g. tuberculosis or pneumonia). Other common causes of coughing (e.g. using an ACE-inhibitor for hypertension) occurs in up to 15% of patients. 

The three most common causes of coughing are as follows:

• Post-nasal drip (41-58%)
• Asthma (24-59%)
• Gastro-oesophageal reflux disease (21-41%)

The most common global cause for a chronic cough is upper airway cough syndrome (UACS) due to a post-nasal drip, asthma or gastro-oesophageal reflux disease (GORD). 

Chronic obstructive pulmonary disease (COPD), tuberculosis (TB) and pulmonary fibrosis (a rare condition in which the soft, spongy parts of the lungs get very stiff) are other important medical conditions associated with coughing.  

Course and prognosis of coughing

Most coughs are self-limiting in that they occur for a few days and then go away on their own. 

Generally, nothing will make the cough go away faster – over-the-counter medication and home remedies only help with reducing the intensity of the cough (if at all). 

But this isn’t to say that these acute coughs aren’t highly irritating and frustrating. Some “non-dangerous” coughs such as a post-viral cough can last for weeks with little to help reduce the coughing, except waiting it out. 

If a foreign body is causing the cough, the cough should settle quickly once the substance has been removed, especially if no damage to the lung lining has occurred. In asthma and COPD, treatment with appropriate inhaled medication usually results in the cough subsiding within days of starting treatment (especially in the case of asthma).

For more severe causes of cough such as tuberculosis, treatment may only result in the symptoms going away after a few weeks. For a condition such as pulmonary fibrosis or even lung cancer, where there has been irreversible damage directly to the lung, the cough may never resolve. 

Reviewed by Professor Richard van Zyl-Smit, Head of the Lung Clinical Research Unit at the University of Cape Town. MBChB, MRCP(UK), Dip HIV(Man), MMED, FCP(SA), Cert Pulm(SA), PhD.

 

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Cough Expert

Professor Keertan Dheda has received several prestigious awards including the 2014 Oppenheimer Award, and has published over 160 peer-reviewed papers and holds 3 patents related to new TB diagnostic or infection control technologies. He serves on the editorial board of the journals PLoS One, the International Journal of Tuberculosis and Lung Disease, American Journal of Respiratory and Critical Medicine, Lancet Respiratory Diseases and Nature Scientific Reports, amongst others. Read his full biography at the University of Cape Town Lung Institute.

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