An inflammatory disease of the lungs characterized by reversible airway obstruction. The tubes that carry air in the lungs are called bronchi and bronchioles. In asthma these tubes become narrowed because of abnormal muscular contraction of the tubes and from inflammation. The lining of these tubes become irritated and secrete mucous and white blood cells into the airways, making the narrowing worse. In some patients this narrowing occurs in response to an irritant such as cold air, dust, pollen, exercise, or tobacco smoke. The severity of symptoms varies greatly among patients.