Asthma (AZ-ma) is a common chronic inflammatory disease that narrows the airways. Asthma affects people of all ages, but it most often starts during childhood. Asthma has no cure. Even when you feel fine, you still have the disease, and it can flare up at any time. If you have asthma, the inside walls of your airways become sore and swollen. That makes them very sensitive, and they may react strongly to things that you are allergic to or find irritating.