Allergy Skin Test

What should I expect before an allergy skin test?

Before your allergy skin test, you’ll meet with a healthcare provider. They’ll ask questions about your symptoms and may perform a physical examination. They may also ask you questions about your diet, what medications you’re taking, what products you use on your skin and if you spend time around particular animals. They’ll also give you specific instructions before your appointment. These may include:

• Don’t apply any skincare products to your testing area on the day of your appointment.
• Don’t take certain medications, including prescription or over-the-counter (OTC) antihistamines.
• Shave away the hair from your testing area the night before or the morning of your procedure.
• Wear a button-down or sleeveless shirt that allows your provider to access the testing area easily.
• If your hair reaches below your shoulders, tie it up or tuck it under a hat.

Should I shower before or after a skin allergy test?

You may shower before your allergy skin tests, but you shouldn’t apply any skincare products to your testing areas.

You can’t shower, swim or participate in any physical activities that cause you to work up a sweat for several days after a patch test.

What are the three types of allergy skin tests and how are they administered?

There are three types of allergy skin tests. Before each test, your healthcare provider will first clean a test area of your skin with iodine or alcohol to reduce the risk of infection. The test area is generally on your forearm or upper back. In some cases — usually with young children — the provider may also apply a numbing cream.

The tests include:

Skin prick (scratch) test

A skin prick test exposes your body to small amounts of possible allergens. It’s the most common type of allergy skin test. Providers use it to test for airborne allergies (such as pollen, dust, mold and animal dander) and food allergies. They may also use skin prick testing as an initial test for stinging insect venom, penicillin and other medication allergies and follow up with intradermal testing.

Your provider will use a marker to label your arm with possible allergens. They’ll then use a thin needle (lancet) to prick your skin near the labels with small amounts of liquids that contain different possible allergens. The lancet won’t go deep into your skin — most people describe the feeling as a tiny pinch.

Some providers may place droplets of possible allergens on your skin and use a lancet to scratch the surface gently. The droplets enter your skin through the scratch.

Your provider will also apply positive and negative controls on your skin. These help your provider compare reactions. A positive control contains a histamine solution. The histamine solution causes an itchy, raised spot (wheal) on your skin shortly after exposure. A negative control contains a saline solution. The saline solution won’t cause a wheal to develop.

After the test, you’ll wait about 15 minutes. Then, your provider will measure any wheals or discolored spots on your skin with a ruler.

A skin prick test takes less than an hour.

Intradermal test

During an intradermal test, a provider uses a tiny needle to inject possible allergens into the outer layer of your skin (epidermis). Providers use intradermal tests to check for airborne allergies, medication allergies and venom/stinging insect allergies (such as bees, fire ants and hornets) if initial skin prick testing is negative or questionable.

Your provider will first use a marker to label your arm with the possible allergens. The test then occurs in two stages.

In the first stage, they’ll insert tiny amounts of possible allergens just under your skin, next to the labels. You’ll then wait about 15 minutes before the provider measures any wheals or discolored spots of skin with a ruler.

• You won’t need additional intradermal testing if you test positive for a specific environmental allergen.
• If you test negative for an environmental allergen, you aren’t allergic to that allergen, and you don’t need further testing.
• If you test negative for a medication, you may move on to a second intradermal test.
• If you test negative for stinging insect venom, then you’ll move on through up to three more sets of intradermal tests. Each test will be a little stronger than the previous test.

In the second stage, your provider will insert a stronger solution of any allergens for which you test negative. You’ll wait another 10 minutes, and they’ll measure any reactions again.

An intradermal test isn’t very painful — most people say it’s less painful than skin prick tests. Depending on how many intradermal tests you need, this type of testing takes about 60 to 90 minutes to complete.

Patch test

During a patch test, a healthcare provider applies bandages (patches) on your skin that contain possible allergens. They help determine the cause of contact dermatitis.

Your provider will first ask what kinds of soaps, lotions, makeup and jewelry you use. They’ll then customize patches of possible allergens, which stick to your back. You leave the patches on for two to four days, and then your provider removes the patches to check for allergic reactions. They’ll compile your allergies into a list and recommend products that are safe for you to use.

What should I expect after an allergy skin test?

Depending on the severity of your allergies, you may have wheals on your skin for as little as a few minutes or up to several days. You may also have other allergy symptoms, including watery eyes, congestion or sneezing. Your healthcare provider will tell you when you can continue taking allergy medications.

What are the risks of an allergy skin test?

Though rare, the biggest risk during an allergy skin test is having an anaphylactic reaction to an allergen. Your provider can recognize and treat severe allergic reactions with an epinephrine injection.