An allergy test is used to help identify a substance – an allergen – that may trigger an allergic reaction. The main forms of allergy tests are skin, elimination and blood tests. Skin tests generally involve applying or injecting a small amount of a suspected allergen to the skin and observing the response. An elimination test is a diet that removes suspected allergy-causing food from the diet and reintroduces each one gradually over time to measure any reaction. An elimination test may also involve offering a food to be tested and a harmless substance in the same session. A blood test involves the taking of a blood sample and then analyzing it for the presence of specific antibodies that would indicate an allergy.