Antibodies are supposed to protect our bodies against viruses, parasites and infections. But for people with an allergy, their immune system mistakenly identifies the particular allergen as an invader and begins to create antibodies against it. These antibodies, called IgE, attach themselves to mast cells, which are abundant under the surface of the skin and in the nose, eyes, lungs and gastrointestinal tract. When the allergen is encountered, the IgE antibodies grab it, triggering the mast cells to release powerful chemicals, including histamine. This causes the allergic reaction. A reaction often occurs within minutes or up to a few hours after contact and may lead to many different symptoms.