Cough

Updated 16 November 2016

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 is not necessarily a sign of approaching illness. It is a vital mechanism in the body’s defence against disease. It can be merely a once-off effort of the body to clear the air passages. Or it could be a chronic cough that could last for months, or sometimes years.

Explosive manoeuvre

The causes of coughing are varied and many, and it can also be a symptom of many different conditions.

A cough is one of the most common symptoms that prompt people to visit the doctor, according to the Merck Manuals. They describe a cough as an "explosive expiratory manoeuvre that is reflexively or deliberately intended to clear the airways".

Coughing can be both a reflex action or deliberate. It is aimed at clearing the throat and the air passage of inhaled irritants, such as dust or dirt particles, excess secretions such as mucus, or capsaicin-like compounds, such as those found in chillies. Certain chemicals, such as swimming pool chlorine, can also make some people cough.

Irritation of the air passage and the lungs can activate the cough receptors present in the respiratory tract, in the oesophagus, the diaphragm and the stomach.

There are three steps to a cough reflex:

1. In order to cough, air needs to be inhaled into the air passages with the glottis (the vocal cords and the opening between them) open. It is the middle part of the larynx.

2. Then air is forced out of the lungs and air passage (by a forceful contraction of the muscles of the chest cage, the abdomen and the diaphragm, according to Harvard Health Publications), with the glottis closed.

3. When the glottis opens, there is an explosive release of air, giving different types of cough their characteristic sound.

The air is expelled at speeds of up to 960km/h, expelling harmful substances from the respiratory tract.

If a cough becomes persistent, it is best to have a doctor examine you to determine the cause.



Read more:

Causes of a cough

Types of cough

Treating a cough

Image: Woman coughing from Shutterstock

 

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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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