Allergens are things that cause allergies. These allergens may be the trigger that starts an asthma attack. 

There are many types of allergens and ways people react to them. Identifying all triggers for asthma can be very difficult.

Allergens may include substances in the environment such as dust mites, mold, pollen, pets, insects, other bugs and other pests.

They may also include viral infections.  Two of the most common are respiratory syncytial virus (RSV) and parainfluenza virus.

In babies, food is more likely to cause allergies.

Tobacco smoke may cause up to 26,000 new cases of asthma each year.  California is one of the leaders in the prevention of second hand smoke exposure, yet we are not where we would like to be and more education is still needed to prevent children from being exposed to secondhand smoke.  Find out more about the harmful effects of tobacco at Tobacco Control Project .