Immunoglobulin E (IgE) is a type of protein in the body called an antibody. As part of the immune system, it plays a role in allergic reactions. When a person is allergic to a particular substance, such as a food or dust, the immune system mistakenly believes that this usually harmless substance is actually harmful to the body. In an attempt to protect the body, IgE is produced by the immune system to fight that particular substance. This starts a chain of events leading to allergy symptoms. In a person whose asthma is triggered by allergic reactions, this chain of events will lead to asthma symptoms, too.