Allergy testing often involves at least one type of skin tests. The different types of skin tests all work along the same principle. The doctor or nurse will introduce different allergens to your skin and wait to see if there is some physical sign of an allergic reaction. Depending on the allergen and the severity of your allergy, the reaction could happen within moments or could take several days.
What you should expect during the appointment will differ according to the type of skin test or tests used.
Skin Prick Test
A skin prick test is the most noninvasive option for testing multiple potential allergies at once. The doctor or nurse will gently poke your skin with needles coated in each allergen and wait for a potential response, which should only include a small red mark. More than 40 different allergies can be tested with the prick test including environmental allergens like dust and hay or foods like milk or wheat.
Adults usually receive the tests on an arm while children get tested on the back due to the larger surface area. The doctor needs to spread out the test sites to make the results clear and will also do pricks with needles containing histamine and saline. The histamine prick should cause a reaction. If it doesn’t, your immune system might not react typically to allergens and you might require further testing. The saline tests to see if you have overly sensitive skin, which can also cause false results.
After the skin prick test is complete, the doctor will rub off the allergens using an alcohol wipe to ensure you don’t continue to react to anything.
Some allergens don’t cause a reaction simply by coming into contact with the skin. Doctors can test for these deeper allergies like penicillin, other medications, or venom allergies by conducting a skin injection test. The test works similarly to the prick test but here the needle actually punctures the skin to inject some of the allergens. The test also usually only involves one or two tests rather than the potential 40 of the prick test.
A patch test is rather the opposite of a skin injection test in that the patches only test for allergens that cause a dermatological reaction. Perfumes, laundry detergent, and makeup are a few examples of potential patch test subjects. The substance is simply rubbed onto the surface of your skin in a small patch and allowed to sit for up to half an hour to check for a response. Like the skin injection test, the patch test typically only tests one or two substances at a time.