Allergen An allergen is a substance that's capable of producing an allergic reaction. In some people with asthma, allergens that are breathed in can trigger symptoms such as coughing, wheezing, and shortness of breath. Allergens that commonly cause asthma symptoms include animal dander, dust mites, mold, and pollen. Back to Articles Related Articles Note: All information is for educational purposes only. For specific medical advice, diagnoses, and treatment, consult your doctor. © 1995-2021 KidsHealth®. All rights reserved. Images provided by The Nemours Foundation, iStock, Getty Images, Veer, Shutterstock, and Clipart.com.