Skin testing is the most common type of allergy test. In percutaneous or prick testing, allergen solutions are placed on the skin, and the skin is then pricked with a needle, allowing the allergen to enter the skin and become exposed to mast cells. Scratch testing, in which the skin is scratched instead of punctured, is used less often. Intradermal testing involves directly injecting allergen solutions into the skin. In both tests, a reddened, swollen spot develops at the injection site for each substance to which the person is sensitive.
Skin reactivity is seen for allergens regardless of whether they usually affect the skin.
In other words, airborne and food allergens cause skin reactions equally well. Provocation testing is done to positively identify suspected allergens after preliminary skin testing. A purified preparation of the allergen is inhaled or ingested in increasing concentrations to determine if it will provoke a response. Food testing is much more tedious than inhalation testing, since full passage through the digestive system may take a day or more. While allergy tests are quite safe for most people, the possibility of a condition known as anaphylaxis does exist.