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Allergy test. View of an arm with several patches held to it used to establish sensitivity to certain allergens. This type of test is called a patch test. Small amounts of a variety of common allergens, such as pet hair, pollen and house dust, are placed onto various sites on the patches. The patches are then stuck onto the patient's skin. Allergic reactions result in the development of areas of inflamed skin. The position of inflammation denotes the allergens to which the patient is sensitised. Although some allergic conditions may be alleviated by drugs, usually diet or behaviour is altered to lessen exposure to the allergens. (KEYSTONE/SCIENCE PHOTO LIBRARY/MIKE DEVLIN)