Updated 25 January 2019

What causes asthma?

There are two distinct phases of asthma that you need to be aware of if you have this condition.

Asthma is caused by a combination of genetic and environmental factors (see articles on risk factors and asthma triggers).

There are two distinct phases to take note of:

Phase 1: Airways partially closed due to inflammation
The airways of asthmatics are always partially closed due to chronic inflammation.

Phase 2: Closing of the airways due to severe inflammation in an acute attack
If anything that triggers or provokes asthma is inhaled and reaches the red, swollen, sensitive inner layers of the airways (the bronchi), the outer muscles constrict, squeezing the already semi-blocked airways nearly completely shut.

The openings in the airways become so narrow that a wheezing or whistling sound is heard.

The underlying, ever-present inflammation may be so widespread in some asthmatics that the airways may be half-closed without them even realising it.

It’s absolutely essential that this chronic inflammation is reduced with the help of daily controller treatment. This will help to control symptoms and prevent permanent damage to the airways.

Reviewed by independent healthcare consultant Prof Praneet Valodia and pulmonologist Prof Elvis Irusen, Head of the Division of Pulmonology at the Faculty of Medicine and Health Sciences, Stellenbosch University. October 2018.

Read more:

- Asthma risk factors

What is asthma?


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Professor Keertan Dheda has received of 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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