Asthma is a chronic lung disorder that causes airways (the tubes that carry air into and out of the lungs) to become inflamed, which means that they swell and produce lots of thick mucus. The muscles surrounding the airways also tend to tighten, which makes the already clogged airways even narrower. This results in asthma symptoms, which can include coughing, wheezing, and shortness of breath. In a person with asthma, the airways are overly sensitive to certain things (such as allergies, viral infections, cold air, exercise, and smoke) that can "trigger," or bring on, asthma symptoms. 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.