Asthma is caused by swelling (inflammation) in the airways. When an asthma attack occurs, the lining of the air passages swells and the muscles surrounding the airways become tight. This reduces the amount of air that can pass through the airway.
In people who have sensitive airways, asthma symptoms can be triggered by breathing in substances called allergens or triggers.
Common asthma triggers include:
- Animals (pet hair or dander)
- Dust mites
- Certain medicines (aspirin and other NSAIDS)
- Changes in weather (most often cold weather)
- Chemicals in the air or in food
- Respiratory infections, such as the common cold
- Strong emotions (stress)
- Tobacco smoke
Substances in some workplaces can also trigger asthma symptoms, leading to occupational asthma. The most common triggers are wood dust, grain dust, animal dander, fungi, or chemicals.
Many people with asthma have a personal or family history of allergies, such as hay fever (allergic rhinitis) or eczema. Others have no history of allergies.