The Definition of an Allergy Skin Test
Skin tests are commonly used to determine if a person has allergies to certain substances. It is often the fastest and safest way to find out what is causing your allergy symptoms. This test involves applying small amounts of a concentrated allergen to a patch of skin, scratching or prickling it in advance to increase exposure. Other forms of skin tests include injecting an allergen under the skin or applying medical patches containing the allergen on the skin, depending on the type of allergy that needs to be determined. A prick or scratch skin test is usually done on the inner side of the forearm or on the back, and the whole procedure will take 40 minutes to one hour of time. Patch test will take longer, up to a 48 hour time period to determine if any allergic reaction symptoms are taking place.
Allergy Skin Test Types
There are three main types of skin tests designed to determine what allergies the patient is having.
These types include:
- Scratch Test - Also known as prick test or puncture test, is when different allergens are applied to several areas of the skin that was intentionally exposed by damaging the outer layer of epidermis. This test is made on the skin of the forearm or the back. The skin surface if sterilized with alcohol, and the skin is either marked with numbers showing the location of specific allergen placement, or a table is drawn to indicate where each different allergen will be placed. A single drop of concentrated allergen - animal dander, plant pollen or mushroom spore extract, insect venom, or other general allergens - is applied to each dedicated patch of skin. After 10 to 15 minutes, the doctor will inspect the skin to see if any of the "zones" show allergic reaction symptoms - redness, swelling or hives - thus making the person allergic to the substance applied to this zone.
- Patch Test - This method involves using a special medical patch containing an allergen to determine if you have a form of allergic contact dermatitis. The patient wears one or several patches for a period of 48 hours, and if by the end of that time the skin under the patch becomes red, irritated, or itchy, that means the person is allergic to the substance used in that particular patch.
- Intradermal Test - In this test, a small amount of allergen is injected under the skin (not in the vein or muscle) to see if it will produce an allergic reaction. This test usually does not involve many different skin injections - only a limited amount of substances are tested using this method. The results usually show in less than 5 minutes.