Asthma is an inability to breathe properly. When any person inhales, the air passes into the lungs through progressively smaller airways called bronchioles. The lungs contain millions of bronchioles, all leading to alveoli -- microscopic sacs where oxygen and carbon dioxide are exchanged. Asthma is a chronic condition in which these airways undergo changes when stimulated by allergens or other environmental triggers that cause patients to cough, wheeze, and experience shortness of breath.