Asthma is a long term illness of the lungs that causes the tubes that carry air into and out of the lungs (airways) to become swollen (inflamed) and produce lots of thick mucus.
In a person with asthma, the lung swelling (inflammation) makes the airways “twitchy”; this means they close easily with certain things like viral infections, cold air, allergens, exercise, and smoke.
This makes the already clogged airways even narrower and can “trigger,” or bring on, asthma symptoms including coughing, whistling noise from the chest (wheezing) and shortness of breath.
People with asthma often find that their symptoms come and go. When the symptoms are present, it’s known as a flare, flare-up, episode, exacerbation, or attack. But even between attacks the airways are swollen because of the allergic inflammation that is present (see what is an allergy).