Asthma is a condition that affects the smaller airways (bronchioles) of the lungs. From time to time the airways constrict (narrow) in people who have asthma. This causes the typical symptoms. The extent of the narrowing, and how long each episode lasts, can vary greatly.
Asthma can start at any age, but it most commonly starts in childhood. At least 1 in 10 children, and 1 in 20 adults, have asthma. Asthma runs in some families, but many people with asthma have no other family members affected.See more..