Immunoglobulin E (IgE) is a type of antibody. Antibodies are proteins that the body forms to help fight invaders, known as pathogens. There are several kinds of antibodies that the body can make. IgA antibodies are typically found in mucous membranes, such as the mouth and the intestinal linings. IgA is also found in breastmilk and can transfer from mother to baby. IgD antibodies are less understood and signal certain immune cells to activate. IgM antibodies are the first antibodies the body makes when exposed to a pathogen. And IgG antibodies take longer to make but are the antibodies we typically think of that are associated with immunity to diseases.

IgE antibodies are normally beneficial because they help protect against parasites. However, IgE antibodies are also responsible for allergic reactions. When the body encounters an allergen for the first time, it develops IgE antibodies that are targeted against that allergen. The IgE antibodies then attach to the surface of immune cells called mast cells and basophils. The next time the body is exposed to the same allergen, the allergen links up with the IgE antibodies, beginning a series of events that result in allergy symptoms.