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Skin prick allergy test. Close-up of the arm of 30-year-old woman undergoing allergy testing using the skin prick method. Solutions containing different allergens, such as pollen and dog hair, are placed in drops on the persons forearm. Each location is labelled and the skin is then pricked with a needle to allow the allergen to enter the body. If the patient is allergic to any of the allergens the skin around that site of application will become inflamed and swollen. (KEYSTONE/SCIENCE PHOTO LIBRARY/DR P. MARAZZI/SCIENCE PHOTO LIBRARY)