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Cough

Updated 15 August 2018

What is a cough?

Coughing is a normal reflex and a result of the stimulation of the cough receptors. But it can also be a symptom of underlying disease.

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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.

Conditions associated with coughing
A cough can be associated with numerous conditions from other body systems (i.e. not just the lungs and the rest of the respiratory system). It’s important to remember that coughing is a symptom, and that the cause of the disorder resulting in the cough should be established.

Listed below are some conditions that may present with coughing, or which have cough as part of their presenting symptoms:

Cardiac conditions

  • Heart failure

Respiratory conditions 

  • Upper respiratory tract infections (e.g. sinusitis, pharyngitis, laryngitis)
  • Lower respiratory tract infections (e.g. pneumonia)
  • Pulmonary embolism
  • Foreign bodies in the respiratory system
  • Cancers
  • Tuberculosis

Digestive system

  • Gastro-oesophageal reflux disease (GORD)

Other causes that should be considered

  • Medications, especially hypertension medication like enalapril (angiotensin converting enzyme or ACE inhibitors)
  • Environmental conditions, e.g. pollution, mining of asbestos (which can lead to asbestosis, a lung disease)

Read more:
How common is coughing?

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. February 2018.

 

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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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