In an allergic reaction, the immune system responds to the allergen by producing a highly specific antibody called immunoglobulin E (IgE). While everyone has IgE antibodies, a person who is allergic has an overabundance of them. When the IgE antibodies attack the allergens, they trigger mast cells, or defensive white blood cells, to release histamine and other chemicals that produce the allergic symptoms of inflammation: swelling, mucous production, itching, rash, hives, or other symptoms, depending on the type and location of the allergy.