Asthma is a chronic disease that causes the airways - the tubes that carry air in and out of your lungs - to become sore and swollen. In the United States, about 20 million people have asthma . Nearly 9 million of them are children. Children have smaller airways than adults, which makes asthma especially serious for them. Children with asthma may experience wheezing, coughing, chest tightness and trouble breathing, especially early in the morning or at night. Many things can cause asthma, including Allergens - mold, pollen, animals Irritants - cigarette smoke, air pollution Weather - cold air, changes in weather Exercise Infections - flu, common cold When asthma symptoms become worse than usual, it is called an asthma attack. Asthma is treated with two kinds of medicines: quick-relief medicines to stop asthma symptoms and long-term control medicines to prevent symptoms.