BAsic information description Asthma involves blockage of normal airflow into and out of the lungs. The blockage develops when certain allergens or irritants are inhaled and cause a reaction in the airways. They become swollen (inflamed), produce excess mucus, and the airway muscles tighten. This leads to the wheezing and other symptoms. Asthma affects all ages, but 50% of the cases are in children under age 10. Boys with asthma outnumber girls. In adult-onset asthma, women are more often...