Asthma is a chronic disease that causes the airways to your lungs to become inflamed and constrict. When this happens, it decreases the amount of air that flows into and through your lungs, causing symptoms such as wheezing, tightness in the chest, and difficulty breathing. Although asthma cannot be cured, it can be controlled and, in some cases, prevented. Although the condition affects people of all ages, it often starts in childhood and is more common in children than adults.