What is an allergy skin test?

An allergy is an overreaction by your immune system to something that doesn't bother most people. An allergy skin test helps find out what is causing your allergic reaction by exposing your skin to allergy-causing substances known as allergens.

Your immune system is your body's defense system. It usually fights germs. But when you have an allergy, your immune system sees a harmless substance, like dust or pollen, as a threat. Your immune system responds to this "threat" and causes an allergic reaction. Symptoms of an allergic reaction can range from sneezing and a stuffy nose to a life-threatening condition known as anaphylactic shock.

During an allergy skin test, your health care provider will expose your skin to a suspected allergen to see if you have an allergic reaction. Substances that could cause an allergic reaction can include:

• Pollen
• Dust mites
• Molds
• Pet dander
• Food
• Insect bites and stings
• Medicines
• Household chemicals

The overreaction an allergy causes is also known as a hypersensitivity of your immune system. There are four main types of overreactions, known as Type 1 through Type IV hypersensitivities. Type 1 hypersensitivity causes some of the most common allergies. These include dust mites, pollens, foods, and animal dander. Other types of hypersensitivities cause different immune system overreactions. These range from mild skin rashes to serious autoimmune disorders.

An allergy skin test usually checks for allergies caused by Type 1 hypersensitivity. The test looks for reactions to specific allergens that are placed on the skin.

Other names: type 1 hypersensitivity skin test, hypersensitivity test allergy scratch test, allergy patch test, intradermal test, prick test, puncture test

What is it used for?

An allergy skin test is used to diagnose certain allergies. The test can show which substances (allergens) are causing your allergic reaction. This can help your provider plan how to treat your allergy.

Why do I need an allergy skin test?

Your provider may order allergy testing if you have symptoms of an allergy. These include:

• Stuffy or runny nose
• Sneezing
• Itchy, watery eyes
• Hives, a rash with raised red patches
• Diarrhea
• Vomiting
• Shortness of breath
• Coughing
• Wheezing

What happens during an allergy skin test?

You will most likely get tested by an allergist or a dermatologist. You may get one or more of the following allergy skin tests:

An allergy scratch test, also known as a skin prick test, is the most common allergy skin test.

During the test:

• Your provider will place small drops of specific allergens on different areas on your skin, such as your forearm or back.
• Your provider will then lightly scratch or prick your skin through each drop.
• If you are allergic to any allergens, you will develop a hive or a small red bump, known as a wheal, at that area or areas within about 15 to 20 minutes.

An intradermal test may be used to see if you are allergic to insect stings and the medicine penicillin. Food allergies are not tested with this method. You need to use more of the allergen to test for food allergies, and that raises the risk of severe reactions such as anaphylactic shock.

During the test:

• Your provider will inject a small amount of allergen just below the skin surface, using a tiny, thin needle.
• Your provider will watch the spot for a reaction. If you are allergic to any allergens, you will develop a hive or a small red bump, known as a wheal, at the area or areas within about 60 to 90 minutes.

This test is sometimes used if your allergy scratch test is negative, but your provider still thinks you might have an allergy.

An allergy patch test checks to see if you have an allergic reaction to allergens that come in contact with your skin. Your provider may ask what soap, lotion, or makeup you use.

During the test:

• Your provider will place small patches on your skin. The patches look like adhesive bandages. They contain small amounts of specific allergens. You'll be asked to avoid getting the testing area wet.
• You'll wear the patches for 48 to 96 hours and then return to your provider's office.
• Your provider will remove the patches and check for rashes, a condition called contact dermatitis, or other reactions.

Will I need to do anything to prepare for the test?

You may need to stop taking certain medicines before the test. These could include antihistamines and certain antidepressants. Your provider will tell you which medicines to avoid before your test and for how long. They may also ask about any products you use on your skin and if you are normally around animals.

If you are having a patch test, your provider may want you to avoid heavy sun exposure and tanning for at least two weeks before the test.

If your child is being tested, the provider may apply a numbing cream to their skin before the test.

Are there any risks to the test?

There is very little risk to having allergy skin tests. The test itself is not painful. The most common side effect is red, itchy skin at the test areas.

In very rare cases, an allergy skin test may cause anaphylactic shock. This is why skin tests must be done in a provider's office where emergency equipment is available. If you've had a patch test and feel intense itching or pain under the patches once you are home, remove the patches and call your provider.

What do the results mean?

Test results are usually reported as positive or negative:

• If you have red bumps or swelling at any testing areas, the test is positive. This means you are probably allergic to those substances. Usually, the larger the reaction, the more likely you are to be allergic.
• If you do not have red bumps or swelling at any of the testing areas, the test is negative. This means that you are probably not allergic to those substances.

If you are diagnosed with an allergy, your provider will recommend a treatment plan. The plan may include:

• Avoiding the allergen when possible
• Medicines
• Lifestyle changes such as reducing dust in your home

Your provider will consider your symptoms and medical history to understand the results of an allergy skin test. They may also want to do a physical exam.

Learn more about laboratory tests, reference ranges, and understanding results.

If you are at risk for anaphylactic shock, you may need to carry an emergency epinephrine treatment with you at all times. Epinephrine is a drug used to treat severe allergies. It comes in a device called an epinephrine auto-injector that contains a premeasured amount of epinephrine. If you experience symptoms of anaphylactic shock, you should inject the device into your skin and call 911.

Is there anything else I need to know about an allergy skin test?

Your provider may recommend an allergy blood test instead if you:

• Have a skin condition such as severe eczema or psoriasis on your arms and back where the skin is usually tested
• Are taking medicines that might interfere with test results
• Have had a severe allergic reaction in the past