What Causes Asthma?

While there is no known specific cause of asthma, what all people with asthma have in common is chronic airway inflammation. Their airways are highly sensitive to various triggers. When their airways come into contact with a trigger, the airways become inflamed (they fill with mucus, swell, and narrow). Then muscles within the airways contract, causing even further narrowing of the airways. This makes breathing difficult and results in an asthma attack.

Triggers are different for different individuals. Common ones include the following:

• Exposure to tobacco smoke



• Breathing polluted air



• Inhaling irritants such as perfume and cleaning products



• Allergens such as molds, dust, and animal dander



• Exposure to cold, dry weather



• Stress



• Exercise or physical exertion



• Medications including aspirin and nonsteroidal antiinflammatory drugs, such as ibuprofen



• An upper respiratory infection such as a cold, flu, or bronchitis



• Sulfites (additives to some foods and wines)

Changes in weather can also trigger asthma attacks because of the irritants and allergens stirred up by wind and rain.

Asthma is on the rise in the United States and other developed countries. While the reasons are not clear, the following factors may contribute to the rise:

• Spending more time indoors where exposure to indoor allergens such as dust and mold and some chemicals from building materials is greater



• Living in cleaner conditions than people did in the past, which makes our immune systems more sensitive (reactive) to triggers



• Exposure to increased air pollution



• Increased physical inactivity (lack of exercise)