Itchy eyes, sneezing or skin rash? These are common signs of an allergic reaction. Allergy symptoms are caused by exposure to allergens—and you may be allergic to only one, or several. If you’re allergic to a certain tree pollen or mold, you’ll have seasonal allergies. If it’s pet dander from dogs and cats, you may have symptoms year round. Most symptoms are just annoying. But a severe allergic reaction called anaphylaxis requires emergency treatment.