A person receiving a skin prick test (SPT). An SPT is performed by using a needle to place a tiny amount of liquid allergen just under the skin of the forearm. SPTs are safe and the results, a raised bump with redness around it (called a wheal and flare), usually appear within 30 minutes. A number of allergens can be tested with an SPT, including ragweed, house dust mite, cat, grass, egg, milk, and peanut. National Institute of Allergy and Infectious Diseases (NIAID)