An asthma trigger is a factor that can lead to sudden difficulty breathing or other symptoms of asthma (asthma attack).

Some triggers are substances a person may be allergic to (allergens). Allergens cause the body's natural defenses (immune system) to produce chemicals called immunoglobulin E (IgE) antibodies. These chemicals bind to allergens, causing inflammation of the bronchial tubes, which carry air to the lungs. The allergen may also cause asthma attacks. These triggers include:

• Pollen.
• Dust mites.
• Animal dander.
• Cockroach droppings.
• Mold.

Other triggers can cause asthma symptoms without affecting the body's immune system. These include:

• Cigarette smoke and air pollution.
• Viral infections, such as colds and influenza, and sinus and other upper respiratory infections.
• Exercise. Many people with asthma have symptoms when they exercise.
• Dry, cold air.
• Medications, such as aspirin or beta-blockers.
• In adults, hormones, including those involved in pregnancy and menstrual periods (just before or during periods).
• Gastrointestinal reflux disease (GERD). Some experts debate whether GERD makes asthma worse. Studies have shown conflicting results as to whether GERD triggers asthma.¹