What is an allergy skin test?
An allergy is an overreaction, also known as a hypersensitivity, of the body's immune system. Normally, your immune system works to fight off foreign substances like viruses and bacteria. When you have an allergy, your immune system treats a harmless substance, like dust or pollen, as a threat. To fight this perceived threat, your immune system reacts 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.
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
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. These substances may include pollen, dust, molds, and medicines such as penicillin. The tests are not usually used to diagnose food allergies. This is because food allergies are more likely to cause anaphylactic shock.
Why do I need an allergy skin test?
Your health care provider may order allergy testing if you have symptoms of an allergy. These include:
- Stuffy or runny nose
- Itchy, watery eyes
- Hives, a rash with raised red patches
- Shortness of breath
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. During the test:
- Your provider will place small drops of specific allergens at different spots on your skin.
- Your provider will then lightly scratch or prick your skin through each drop.
- If you are allergic to any allergens, you will develop a small red bump at the site or sites within about 15 to 20 minutes.
An intradermal test. During the test:
- Your provider will use a tiny, thin needle to inject a small amount of allergen just below the skin surface.
- Your provider will watch the site for a reaction.
This test is sometimes used if your allergy scratch test was negative, but your provider still thinks you have an allergy.
An allergy patch test. During the test:
- A provider will place small patches on your skin. The patches look like adhesive bandages. They contain small amounts of specific allergens.
- 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 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 include antihistamines and antidepressants. Your health care provider will let you know which medicines to avoid before your test and how long to avoid them.
If your child is being tested, the provider may apply a numbing cream to his or her 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 sites. In very rare cases, an allergy skin test may cause anaphylactic shock. This is why skin tests need to 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?
If you have red bumps or swelling at any of the testing sites, it probably means you are allergic to those substances. Usually the larger the reaction, the more likely you are to be allergic.
If you are diagnosed with an allergy, your provider will recommend a treatment plan. The plan may include:
- Avoiding the allergen when possible
- Lifestyle changes such as reducing dust in your home
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 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?
If you have a skin condition or other disorder that prevents you from getting an allergy skin test, your provider may recommend an allergy blood test instead.
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The information on this site should not be used as a substitute for professional medical care or advice. Contact a health care provider if you have questions about your health.