"To fight the substances, your body produces histamines and other chemicals that trigger allergic symptoms, such as a runny nose, irritated eyes or itchy skin.???Allergies [peak] in teens and people in their 20s, [and] again in their 30s and 40s,??? explains Michael Benninger, M.D., chairman of the Head and Neck Institute at the Mayo Clinic in Rochester, Minn.When you develop an allergy, ???you mig" . . . .