What is Skin Testing for Allergies?
During allergy skin tests, your skin is exposed to suspected allergy-causing substances (allergens) and is then observed for signs of an allergic reaction.
Along with your medical history, allergy tests may be able to confirm whether or not a particular substance you touch, breathe or eat is causing symptoms.
Why is Skin Testing for Allergies performed?
Information from allergy tests may help your doctor develop an allergy treatment plan that includes allergen avoidance, medications or allergy shots (immunotherapy).
Allergy skin tests are widely used to help diagnose allergic conditions, including:
- Hay fever (allergic rhinitis)
- Allergic asthma
- Dermatitis (eczema)
- Food allergies
- Penicillin allergy
- Bee venom allergy
- Latex allergy
Skin tests are generally safe for adults and children of all ages, including infants. In certain circumstances, though, skin tests aren’t recommended. Your doctor may advise against skin testing if you:
- Have ever had a severe allergic reaction. You may be so sensitive to certain substances that even the tiny amounts used in skin tests could trigger a life-threatening reaction (anaphylaxis).
- Take medications that could interfere with test results. These include antihistamines, many antidepressants and some heartburn medications. Your doctor may determine that it’s better for you to continue taking these medications than to temporarily discontinue them in preparation for a skin test.
- Have certain skin conditions. If severe eczema or psoriasis affects large areas of skin on your arms and back — the usual testing sites — there may not be enough clear, uninvolved skin to do an effective test. Other skin conditions, such as dermatographism, can cause unreliable test results.
Blood tests (in vitro immunoglobulin E antibody tests) can be useful for those who shouldn’t undergo skin tests. Blood tests aren’t done as often as skin tests because they can be less sensitive than skin tests and are more expensive.
In general, allergy skin tests are most reliable for diagnosing allergies to airborne substances, such as pollen, pet dander and dust mites. Skin testing may help diagnose food allergies. But because food allergies can be complex, you may need additional tests or procedures.
What should I know before receiving Skin Testing for Allergies?
The most common side effect of skin testing is slightly swollen, red, itchy bumps (wheals). These wheals may be most noticeable during the test. In some people, though, an area of swelling, redness and itching may develop a few hours after the test and persist for as long as a couple of days.
Rarely, allergy skin tests can produce a severe, immediate allergic reaction, so it’s important to have skin tests performed at an office where appropriate emergency equipment and medications are available.
How to prepare for Skin Testing for Allergies?
Tell your doctor about all medicines you’re taking, including over-the-counter products. Some drugs can affect the results, so your doctor will give you a list of medicines to avoid before the test.
If you can’t stop taking a medication, your doctor or nurse may do a separate test to find out if that drug will hamper the results.
Since allergy medicines, such as OTC antihistamines, stop allergic reactions, you shouldn’t take them for a few days before your appointment. You need to let your body react to the allergens in the test.
What happens during Skin Testing for Allergies?
Skin testing is usually done at a doctor’s office. A nurse generally administers the test, and a doctor interprets the results. Typically, this test takes about 20 to 40 minutes. Some tests detect immediate allergic reactions, which develop within minutes of exposure to an allergen. Other tests detect delayed allergic reactions, which develop over a period of several days.
Skin prick test
A skin prick test, also called a puncture or scratch test, checks for immediate allergic reactions to as many as 40 different substances at once. This test is usually done to identify allergies to pollen, mold, pet dander, dust mites and foods. In adults, the test is usually done on the forearm. Children may be tested on the upper back.
Allergy skin tests aren’t painful. This type of testing uses needles (lancets) that barely penetrate the skin’s surface. You won’t bleed or feel more than mild, momentary discomfort.
After cleaning the test site with alcohol, the nurse draws small marks on your skin and applies a drop of allergen extract next to each mark. He or she then uses a lancet to prick the extracts into the skin’s surface. A new lancet is used for each allergen.
To see if your skin is reacting normally, two additional substances are scratched into your skin’s surface:
- In most people, this substance causes a skin response. If you don’t react to histamine, your allergy skin test may not reveal an allergy even if you have one.
- Glycerin or saline. In most people, these substances don’t cause any reaction. If you do react to glycerin or saline, you may have sensitive skin. Test results will need to be interpreted cautiously to avoid a false allergy diagnosis.
About 15 minutes after the skin pricks, the nurse observes your skin for signs of allergic reactions. If you are allergic to one of the substances tested, you’ll develop a raised, red, itchy bump (wheal) that may look like a mosquito bite. A nurse will then measure the bump’s size.
After the nurse records the results, he or she will clean your skin with alcohol to remove the marks.
Skin injection test
You may need a test that uses a needle to inject a small amount of allergen extract just into the skin on your arm (intradermal test). The injection site is examined after about 15 minutes for signs of an allergic reaction. Your doctor may recommend this test to check for an allergy to insect venom or penicillin.
Patch testing is generally done to see whether a particular substance is causing allergic skin irritation (contact dermatitis). Patch tests can detect delayed allergic reactions, which can take several days to develop.
Patch tests don’t use needles. Instead, allergens are applied to patches, which are then placed on your skin. During a patch test, your skin may be exposed to 20 to 30 extracts of substances that can cause contact dermatitis. These can include latex, medications, fragrances, preservatives, hair dyes, metals and resins.
What happens after Skin Testing for Allergies?
The doctor or nurse will clean any extracts and ink marks off your skin with alcohol. You may need to use a mild cortisone cream to ease itching.
If you get a patch test, you’ll go home with bandages on your skin. Don’t get these areas wet — no baths or swimming. When you go back to the doctor in a couple of days, he’ll take another look at your skin.
Your doctor or allergist will use the results of your test to come up with a treatment plan for you.
If you have any questions about the Skin Testing for Allergies, please consult with your doctor to better understand your instructions.
Explanation of results
What do my results mean?
A positive skin test means that you may be allergic to a particular substance. Bigger wheals usually indicate a greater degree of sensitivity. A negative skin test means that you probably aren’t allergic to a particular allergen.
Keep in mind, skin tests aren’t always accurate. They sometimes indicate an allergy when there isn’t one (false positive), or skin testing may not trigger a reaction when you’re exposed to something that you are allergic to (false negative). You may react differently to the same test performed on different occasions. Or you may react positively to a substance during a test but not react to it in everyday life.
Your allergy treatment plan may include medications, immunotherapy, changes to your work or home environment, or dietary changes. Ask your doctor to explain anything about your diagnosis or treatment that you don’t understand. With test results that identify your allergens and a treatment plan to help you take control, you’ll be able to reduce or eliminate allergy signs and symptoms.
Depending on the laboratory and hospital, the normal range for Skin Testing for Allergies may vary. Please discuss with your doctor any questions you may have about your test results.
Hello Health Group does not provide medical advice, diagnosis or treatment.
Allergy skin tests. https://www.mayoclinic.org/tests-procedures/allergy-tests/about/pac-20392895. Accessed October 8, 2018.
If You Get Skin Testing for Allergies. https://www.webmd.com/allergies/skin-test#1. Accessed October 8, 2018.
Review Date: November 4, 2018 | Last Modified: September 12, 2019