Asthma is a lung disease that makes breathing difficult for people of all the ages ranging from children to olders. Most often it starts during childhood. To understand asthma one needs to know how airways work. Airways are tubes that carry air into and out of lungs. People who have asthma have inflamed airways. The inflammation makes the airways swollen and very sensitive.

The airways tend to react strongly to certain inhaled substances. When the airways react, the muscles around them tighten.