An allergen is something that triggers an allergy. When a person with allergic rhinitis breathes in an allergen such as pollen, mold, animal dander, or dust, the body releases chemicals that cause allergy symptoms.
Hay fever and allergies often run in families. If both of your parents have hay fever or other allergies, you are likely to have hay fever and allergies, too. The chance is higher if your mother has allergies.