Asthma - Causes - Causes

The exact cause of asthma is unknown, and the causes may vary from person to person. However, asthma is often the result of a strong response of the immune system to a substance in the lungs. To understand asthma, it helps to understand How the Lungs Work.

Normally, the body’s immune system helps to fight infections. Sometimes a person’s immune system responds to a substance in the environment called an allergen. When someone breathes in an allergen, such as ragweed, the immune system in the airways may react strongly. Other people exposed to the same substance may not react at all.

The immune system reacts to an allergen by creating inflammation. Inflammation makes your airways swell and narrow and possibly produce more mucus. This can make it harder to breathe. The muscles around the airways may also tighten, which is called a bronchospasm. This can make it even harder to breathe.

Over time, the airway walls can become thicker. The image below shows how airways narrow during asthma.

Airway narrowing in an asthma attack.
Airway narrowing in an asthma attack. The image on the left shows the location of the lungs in the body. The middle image is a close-up of a normal airway, and the image on the right shows a narrowed, inflamed airway typical of an asthma attack. Medical Illustration Copyright © 2020 Nucleus Medical Media, All rights reserved.

Your asthma may have been caused partly by a viral infection or allergens in the air when you were a baby or young child. During this stage of life, your immune system is still developing.

It’s not clear why one person reacts to an exposure while others do not. Genes seem to play a role in making some people more susceptible to asthma.