Asthma Glossary of Terms Allergen:a substance (such as a food or pollen) that your body perceives as dangerousand can cause an allergic reaction. Allergy:an exaggerated response to a substance or condition produced by the release ofhistamine or histamine-like substances by affected cells. Alveoli:thin-walled, small sacs located at the ends of the smallest airways in thelungs […]