Allergy skin prick or scratch test
One of the most common methods of allergy testing is the scratch, skin, or prick test. The test involves placing a small amount of the suspected allergy-causing substance (allergen) on the skin (usually on the forearm, upper arm, or back), and then scratching or pricking the skin so that the allergen is introduced under the skin surface. The skin is observed closely for signs of a reaction, which usually includes swelling and redness of the site. With this test, several suspected allergens can be tested at the same time. Results are usually obtained within about 20 minutes.