Many things can cause an allergy, from particular food items such as shellfish to pollen and of course insect stings, and some people are more genetically predisposed to developing an allergy than others. The skin allergy test, which comes in various guises, is a way of testing whether someone is allergic to something in particular, such as a certain drug or household substance such as house dust or pet dander.
The basic mechanism behind an allergic reaction involves immunoglobin E (IgE) antibodies, which form an important part of the immune system. These bind to the allergen – the substance causing the allergy – and then to a receptor protein on mast cells or basophils (a type of white blood cell) which triggers the release of inflammatory chemicals such as histamine.
The skin allergy test is a way of diagnosing an allergy by provoking a small, controlled allergic response on the skin. It can involve a skin prick test, where a needle containing a small amount of the allergen is pricked into the skin, a skin scratch test, where the allergen is scratched more deeply into the skin, or by injecting, scraping or applying a patch containing the allergen over the skin.
Skin testing for allergies goes back many years. Perhaps the first person to perform it scientifically was a Lancashire doctor called Charles H. Blackley in 1865. He abraded a small area of his own skin with a lancet, applied grass pollen on a piece of wet lint and covered the scarified area with a bandage. The result was intense itching and inflammation.