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Skin testing is a way to determine what substances a person may be allergic to. Common allergens are pollen, grass, animal dander, food, mold or medication. If a person has a positive reaction to a suspected allergen, then it means that their body is producing an antibody against that irritant.
Skin testing for allergies began in 1865 when Dr. Charles H. Blackley scraped an area on his own arm and then applied grass pollen grains to the abrasion using wet lint. He developed intense itching and his skin broke out demonstrating how the body can have skin response to an allergen placed on the skin. In the 1900’s, other forms of skin testing were developed that have been further refined into the methods used today.
The three types of skin testing are: scratch, intradermal or patch.
Scratch testing is performed by a nurse or a doctor. A drop of the suspected allergen is placed on the forearm (or back) after the area is cleaned with alcohol. A disposable device is used to prick or puncture the skin to push the allergen into the top layer of the skin. Before testing, the areas are pre-marked by drawing a circle in ink where the allergen will be placed and any changes to the skin will be recorded.
Intradermal testing is similar to how a TB test is done. The skin is cleaned with alcohol and the nurse positions the tiny needle attached to a syringe just under the top layer of skin. A small bubble will appear as she injects the liquid that contains the allergen. The area will be observed similar to the scratch test.
Patch testing is used to identify what substance may be causing an allergic skin rash. The patch will trigger itching and irritation if you are allergic to the allergen it contains. Patches are left on for up to 48 hours and will be checked when you return to the doctor. Both scratch testing and intradermal testing are checked about 15-30 minutes after exposure to an allergen, during the same visit to the doctor.
There is minimal risk of having a serious reaction to skin testing.