What is allergy skin testing?

Dr. Susan G. Bershad, MD
Dermatologist (Skin Specialist)

There are 2 types of allergy skin testing. The first is called the skin prick test, usually performed on the arms, which is for type 1 allergies. These reactions occur within seconds to minutes after exposure to allergens and include sensitivities to airborne particles like pollen, dust mites and animal dander, and foods like peanuts, milk, eggs, wheat and soy. This category of allergies causes hives and eczema, also called atopic dermatitis. Type 1 skin reactions begin inside the body and may affect the skin all over the body, even where the substance was not in contact.

The second type of allergy skin testing is patch testing, usually performed on the upper back. Patch testing is for type 4 allergies, also called delayed hypersensitivity or allergic contact dermatitis, which occurs hours to days after exposure. An example of a type 4 allergy is poison ivy. In cases of allergic contact dermatitis, the rash is located where the offending substance came in contact with the skin, and not elsewhere. There are several dozen substances responsible for allergic contact dermatitis that are commonly found in our environment, including nickel, fragrance ingredients, neomycin, latex and formaldehyde. Patch testing will help identify the substances that cause this type of dermatitis in a particular person.

Allergy tests are fairly accurate and can be helpful in identifying specific triggers. In this video, I will discuss the process of allergy testing and how it helps in preventing symptoms.

Allergy skin testing is performed by an allergist, normally in his or her office. During the testing, very small amounts of different allergens such as pollen and dander are injected just under the skin. The patient is then observed to see if there is a reaction to the small amount of allergen. These reactions normally appear as a redness and swelling of the skin in that area or itching in the area the allergen was injected under the skin. This would indicate that the person has an allergy to that substance.

Dr. Paul M. Ehrlich, MD
Allergist & Immunologist
A skin test involves pricking or scratching the skin and then applying possible allergy-provoking substances. If a patient is allergic, the allergen will look like a mosquito bite. Sometimes this may be followed up with an intradermal test below the skin. The tendency is to overtest, which is to order tests that are probably superfluous if a good medical history is taken. These also fall under the heading of annoying because they leave the patient with railroad-tracks of itching up and down their forearms. An alternative to the intradermal test is the percutaneous test or "prick" test which is much faster and less painful.
Asthma Allergies Children: A Parent's Guide

More About this Book

Asthma Allergies Children: A Parent's Guide

Asthma and allergies are at epidemic proportions. It doesn't have to be that way. Two experienced pediatric allergists tell everything a conscientious parent needs to know about these conditions,...

This is a simple test that can be done with minimal discomfort and provides an allergist with a quick answer about whether your body is responding to an allergen, whether it is a pollen, animal dander, mold, food or other allergen. In general, an extract of the protein is introduced into the top edge of the skin on the arm or back with a plastic or metal device that makes a scratch (no bleeding). If your body has recognized the tested item as a possible allergen, a small itchy spot, like a mosquito bite, develops in 10-15 minutes right where the test was done. The allergist also uses a negative comparison and a positive comparison test. The main limitation of the test is that it can be positive in a person that may not have any symptoms when they are exposed to what was tested. That is why the allergist must do a complete history prior to any testing, to consider if your symptoms are allergic, what may be triggering them, and then decide upon what should be tested and how to then interpret those test results. This test (and similar allergy blood tests) can be very misleading if they are done to “screen” for allergy without considering the illness under consideration, exposures and their relationship. In some cases, the allergen being tested is injected under the skin with a small needle, but this manner of skin test is usually reserved for special situations and the allergy scratch test (also called prick test) is more often used.

Continue Learning about Allergy Test

What is a radioallergosorbent (RAST) blood test?
A RAST (radioallergosorbent) blood test looks for specific immunoglobulin E (IgE) antibodies in your...
More Answers
What does RAST mean?
Honor Society of Nursing (STTI)Honor Society of Nursing (STTI)
RAST stands for radioallergosorbent test. This is a blood test used to diagnose allergies. Your bloo...
More Answers
What is a skin prick test?
Honor Society of Nursing (STTI)Honor Society of Nursing (STTI)
Your allergist may perform a skin prick test to discover what you are allergic to. The allergist wil...
More Answers
What is ImmunoCAP ISAC?
Paul M. Ehrlich, MDPaul M. Ehrlich, MD
ImmunoCAP (Immuno Solid-phase Allergy Chip) ISAC is the latest thing in allergy testing. Develop...
More Answers

Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.