Patch Test

What is a patch test?

A patch test is a type of allergy test for contact dermatitis, a skin reaction that can develop after exposure to an allergen over several days. It can help your healthcare provider determine the cause of rashes, eczema or other skin irritations.

During a patch test, a provider tapes patches to your skin (usually, your back) that contain small amounts of potential allergens. They’ll remove the patches after two days and check the area again another two days after removal.

When should you get a patch test?

Your provider might recommend a patch test if you:

• Have rashes or eczema and you don’t know the cause
• Want to see if you react to a specific substance that you think might be causing rashes
• Think you might be reacting to materials you use during your job or hobbies (but don’t know the exact cause)
• Want to see if you’ll have a reaction to materials you’ll need to work with at a specific job

What can patch testing look for?

Skin patches can test for many types of substances, including:

• Adhesives
• Fragrances and perfumes
• Disinfectants and antiseptics
• Ingredients used in soaps, shampoos, cosmetics and hair dyes
• Materials used in making clothes or shoes
• Metals (like nickel, cobalt and gold)
• Preservatives
• Plastics and resins (like epoxy or acrylates)
• Rubber and rubber additives
• Topical medications (like antibiotics or steroids)

There are specific patches that include substances you might come in contact with during certain jobs — like hairstyling, healthcare or construction.

How does the patch testing work?

A patch test takes place over about a week. Unlike other types of allergic reactions that happen right after you’re exposed to an allergen, contact dermatitis can take a few days to develop.

On the first day of testing, you’ll have an appointment at your provider’s office (usually an allergist or dermatologist). Your provider will place patches on your back (or sometimes on your arms) that have small amounts of potential allergens on them. Each patch has 10 to 12 substances on it, in a gel or ointment. Your provider tapes the patches to your body so the gels press against your skin.

You’ll need to follow your provider’s instructions for taking care of the area with the patches (test area) after you go home. For example, it’s very important not to shower, sweat or get the patches wet. Moisture can interfere with the results.

Two days later, your provider will remove the patches and check the test area for any allergic reactions. It’s generally safe to shower after your provider removes the patches. But it’s still important to avoid scrubbing or scratching the test area to prevent irritation or affecting the test results. After another two days, you’ll go back to your provider’s office so they can check one more time for any reactions.

Providers often apply patches on a Monday, remove them and check the area on Wednesday, and check the area again on Friday. But your provider will let you know when to come back to the office.

How do I prepare for a patch test?

There are many things to keep in mind to prepare for a patch test:

• Don’t expose the test area to the sun or tanning beds for a week or two before testing.
• Don’t use medicated lotions, creams or ointments on your skin where you’ll have the testing (usually your back) for at least a week before testing.
• Don’t use moisturizers on the test area on the day of or during testing.
• Let your provider know if you’re pregnant. While patch testing won’t hurt you or the fetus, changes in your immune system while pregnant can affect your results.
• Taking antihistamines (allergy pills) before and during the testing is OK. Antihistamines don’t interfere with patch tests.
• Let your provider know if you’re taking prednisone or any other medications that can weaken your immune system. These can affect the results of patch testing.
• Your provider may have you shave body hair on your back and/or arms the night before they place your patches. Use an electric razor to avoid irritating your skin.
• At your first appointment and while the patches are on, wear loose clothing that you can get on and off easily (for example, you might want to wear button-down shirts since you may not be able to lift your arms above your head easily with the patches on).
• At your first appointment and throughout the week of the test, wear dark shirts or ones that you don’t mind getting stained from the ink that your provider uses to mark the patch areas.
• If you have long hair, pull it up off your back for your appointments so it doesn’t interfere with placing or removing the patches.
• Ask your provider if there’s a number you should call if you experience severe discomfort from the patches.

How is a patch test done?

On the first day of the patch test, your provider will:

1. Apply one or more patches to your back
2. Mark the edges of the patches and number them with a marker or pen
3. Cover the area with tape (and sometimes a waterproof covering)

After you’ve worn the patches for two days, your provider will:

1. Remove the patches
2. Note any reactions
3. Re-mark the edges where the patches were

Two more days after that, your provider will check the area again and note any reactions. Your provider won’t replace the patches, but you’ll still need to follow their directions for taking care of the test area until the final check.

What should I do during a patch test?

During the entire week of the test (until your provider does the last check of the test area):

• Don’t move, loosen or remove the patches (unless your provider specifically tells you to)
• Avoid any movements that could loosen the patches
• Avoid heat and activities that could make you sweat
• Don’t scratch or rub at the patches, even if they itch
• Don’t use moisturizers, creams, lotions, soaps or ointments on the test area
• Let your provider know if a patch comes loose or pulls away from your skin
• Don’t expose the patches or test area to sunlight
• Don’t get the patches wet

Unless your provider tells you it’s OK to shower, use a washcloth to clean your body (except where the patches are) and wash your hair in the sink to avoid getting your back wet.

What are the risks of a patch test?

After the test, you may have irritated skin or patches of skin that are lighter or darker than the area around them (discoloration). This should clear up on its own in a few days.

It’s rare, but some people experience severe allergic reactions, like anaphylaxis. This usually happens within a few hours of applying the patches. Ask your provider what symptoms to look out for and when to contact them or get medical attention.

What do the results of patch testing mean?

Your provider will evaluate each substance on the patches individually. They’ll note if you had a reaction and how severe it was by using one or more plus (+) signs. For example, a single plus (+) means you had a mild reaction. Three plus signs (+++) means you had a very strong reaction. They mark any substances you didn’t react to with a minus (-) sign.

When should I know the results of the test?

You’ll know the results of the patch test when your provider checks your skin. Some reactions happen within the first two days of the test (by the time the patches are removed for the first check) and some develop over the next few days after that.

If the results are abnormal what are the next steps?

If your patch test shows you have a reaction to certain substances, your provider will recommend you avoid them and products that contain them. They can give you a list of products that contain the ingredients you’re allergic to and a personalized “safe list” of products that don’t. There are also apps for your phone that help you identify and avoid these ingredients. Your provider can help you download and use one.

Sometimes, your provider will want to repeat the test at a later time if the results are unclear or aren’t as expected.

When should I call my doctor?

Contact your healthcare provider right away if you experience severe itching or pain in the test area. You can ask your provider whether it’s safe to take medications like antihistamines to help relieve itching. Call 911 or your local emergency services number if you experience:

• Severe swelling in the test area
• Swelling of your face, lips, mouth or tongue
• Difficulty breathing or swallowing
• Weakness, light-headedness or dizziness (which could mean a sudden drop in blood pressure)
• Hives over many parts of your body
• Vomiting

How uncomfortable is patch testing?

Patch testing might be somewhat uncomfortable. The patches and tape can restrict your movement, so it might feel strange and keep you from getting comfortable in certain positions. You may have to adjust your sleeping position, for example.

If you’re sensitive to any of the substances, you might feel itching or burning. This shouldn’t be painful. Ask your provider what to expect and if there are any symptoms you should look out for or let them know about. Contact them if you experience severe itching or unexpected symptoms.