In this test, indoor allergens including house dust mite, house dust, mould, cockroaches, cat and dog are routine A few common pollens, seafood, milk and egg are also tested. Known food allergy does not require testing. A positive reaction to the skin prick test occurs when the skin around the needle prick becomes itchy and red with the development of a white swelling called a wheal. The wheal reaches its maximum size in about 15 to 20 minutes and the reaction fades within a few hours.