Causes

Childhood asthma causes aren't fully understood. Some factors thought to be involved include:

• Inherited tendency to develop allergies
• Parents with asthma
• Some types of airway infections at a very young age
• Exposure to environmental factors, such as cigarette smoke or other air pollution

Increased immune system sensitivity causes the lungs and airways to swell and produce mucus when exposed to certain triggers. Reaction to a trigger can be delayed, making it more difficult to identify the trigger. Triggers vary from child to child and can include:

• Viral infections such as the common cold
• Exposure to air pollutants, such as tobacco smoke
• Allergies to dust mites, pet dander, pollen or mold
• Physical activity
• Weather changes or cold air

Sometimes, asthma symptoms occur with no apparent triggers.