People with asthma have very sensitive airways that react to many things, such as cigarette smoke, allergies, infections, or cold air.  Asthma episodes may come and go, but the lungs stay sensitive to the things that trigger asthma. 

Poor control of asthma may lead to frequent emergency room visits or hospital stays.  Poor asthma control can also cause death.

Children's Hospital Patient Information Handout

Next page: What causes asthma?