People with asthma have an underlying condition in their lungs. Their airways, which are rather like hollow branches that bring air into the lungs, are always inflamed are easily irritated by outside triggers. One common cause is exposure to allergens in patients with an allergy.

When this happens, the airways contract and narrow. The cells in the irritated airways also produce more mucus or phlegm, making the airway even smaller. Breathing becomes difficult and that is what is often called an asthma attack.