Asthma: Introduction Asthma: Asthma is a chronic, ongoing lung disease or respiratory condition marked by acute flare-ups or attacks of difficulty with breathing. This includes shortness of breath, cough, chest tightness, and the hallmark wheezing sound, a "whistling" noise that occurs with respirations. It is a common condition that most often occurs during childhood and can continue into adulthood. The onset of asthma can also occur at any age. More than 6 million children and 22 million adults in the U.S. have the condition, according to the National Heart Lung and Blood Institute. Asthma symptoms can range from mild to life threatening. Asthma is a disease of the lower respiratory track. Characteristics include inflammation of the airways in the lungs. These include the bronchioles, small hollow passageways that branch off the main airway from the mouth and nose. Air and oxygen pass through the bronchioles into the alveoli, tiny hollow structures in the lungs where oxygen is absorbed in to the bloodstream. In asthma, bronchioles and alveoli become inflamed, irritated and swollen, blocking the flow of air into the lungs. The surrounding muscles react by tightening and further blocking the flow of oxygen into the lungs and bloodstream. The airway also begins to make more mucus than normal, which further blocks the airways and compounds the problem with the intake of air.