Health A-Z

Medical Content Created by the Faculty of the Harvard Medical School


What Is It?

Asthma is a chronic (long-term) lung condition. Air passages narrow and become inflamed. This leads to breathing difficulties and wheezing.

Asthma ranges from mild to severe. Some people have only occasional, mild symptoms. Others have nearly constant symptoms with severe, life-threatening flare-ups.

During an asthma attack, the airways become inflamed. They narrow as the muscles surrounding them constrict. Mucus produced by the inflammation fills the narrowed passageways. As a result, the flow of air is partially or completely blocked.

Asthma affects the lung's larger and smaller airways.

What causes asthma-related inflammation is not clear. But several environmental "triggers" have been identified.

Many asthma triggers are allergens. Allergens cause the immune system to overreact in some people. Common allergens include:

  • Animal dander and saliva

  • Pollens

  • Molds

  • Dust mites

  • Cockroaches

  • Some medications

  • Certain foods

Also high on the list of asthma triggers are:

  • Viral infections, such as colds and influenza

  • Exercise

  • Breathing cold, dry air

  • Environmental pollutants, such as:

    • Cigarette smoke

    • Wood smoke

    • Paint fumes

    • Chemicals

  • Strong odors

  • Emotional stress

For some people with severe asthma, no specific triggers can be identified.

Asthma can develop early, often before age 5. But its symptoms can begin at any age. The condition has a genetic (inherited) component. It often affects people with a family history of allergies.

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From Health A-Z, Harvard Health Publications. Copyright 2007 by the President and Fellows of Harvard College. All rights reserved. Written permission is required to reproduce, in any manner, in whole or in part, the material contained herein. To make a reprint request, contact Harvard Health Publications. Used with permission of StayWell.

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