When the cause of an allergy is unknown, a skin prick test (also called a puncture or scratch test) can be performed at the doctor's office to identify possible allergens.
Multiple substances are scratched into to the surface of the skin to detect common allergens,including: mold, pollen, pet dander, dust mites and different types of food.
Allergy testing takes less than an hour and can be performed on adults or children of any age. For children the test is usually performed on the upper back. Adults will usually have an allergy test performed on the forearm. First, the nurse will clean the skin with alcohol and mark the test area. The allergen is then applied next to each mark. The needles used to apply the substance only scratches the surface of the skin, so the test is not painful. A different needle is used for each substance.
To check if the skin is reacting normally, a histamine will also be applied to the skin. If you don't react to histamine, which is uncommon, the allergy test may not identify an allergy even if you have one. In addition, glycerin or saline is applied to test for a reaction. If there is a reaction, it is often an indiction of sensitive skin, which muct e factored into the allergy test results to avoid a false diagnosis.
The skin test may detect an allergic reaction immediately, or the reaction may not occur until several days after exposure. If an allergic reaction is present, there will be a raised, red bump on the skin resembling a mosquito bite. The nurse will measure the size of the bump. The marks will then be removed with alcohol. If an allergen is identified, your doctor will discuss the options for treatment.