An IgE test is a blood test done to check whether a person is allergic to a particular substance. An allergic reaction occurs when the immune system overreacts to something, often in the environment, that's harmless to most people. To protect the body from this perceived threat, the immune system of an allergic person produces antibodies called immunoglobulin E (IgE). Because IgE antibodies are unique to each allergen, checking for specific variants in the blood can help determine if an allergy is present. Common allergens that may be tested for by using the allergen-specific IgE test include pollen, mold, dust mites, foods (for instance milk, eggs, or legumes), medications (such as penicillin), insect venom and materials such as latex or animal fur.