Causes/Triggers of Asthma

The exact cause of asthma isn't known. Researchers think a combination of factors (family genes and certain environmental exposures) interact to cause asthma to develop, most often early in life. These factors include:

An inherited tendency to develop allergies, called atopy.
Parents who have asthma.
Certain respiratory infections during childhood.
Contact with some airborne allergens or exposure to some viral infections in infancy or in early childhood when the immune system is developing.

The factors(triggers) that can set off an asthma attack include:

inhaled allergens (such as dust mites, pollen, and cat and dog allergens).
tobacco smoke.
air pollution.
exercise.
strong emotional expressions (such as crying or laughing hard).
chemical irritants.
certain drugs (aspirin and beta-blockers).