Version July 2025
Please read the Disclaimer at the end of this page.
What is patch testing? —
This is putting a small amount of a substance on a patch, then putting the patch on your skin to see if it reacts.
Patch testing can help your doctor figure out:
●If you have allergic contact dermatitis – This is a type of skin rash that can happen after your skin touches something you are allergic to.
●What is causing your allergic contact dermatitis
How do I prepare for patch testing? —
For 2 weeks before your patch test and until you have gone to all your follow-up visits:
●Do not sunbathe – This includes using tanning beds and sitting out in the sun.
●Do not use any steroid medicines – These include steroid creams and pills.
●Follow your doctor's instructions about any other medicines – Talk to your doctor or nurse about whether you need to stop any of your other medicines before your patch test. For example, if you take any medicines to suppress your immune system, you might need to stop them.
These things can make patch testing inaccurate. You do not need to stop taking antihistamines for allergies. They do not affect the test.
Patch testing is usually done on the back. Some people need to trim their back hair 1 to 2 days before the test. The test can also be done on the arms or thighs.
What happens during patch testing? —
Doctors use several types of patch testing. In most cases, the doctor puts a drop of the substance you might be allergic to on a small patch. Then, they tape the patch to your skin. The patch stays on for 2 days.
If your doctor tests many substances at once, they might use a large patch instead of several small patches. The large patch might have numbers on it, or your doctor might write on your skin with a marker. This helps them see which substances you are allergic to.
You will return to the doctor 2 days later:
●They will remove any patches from your skin.
●They will wait 15 to 60 minutes, then look at your skin to see if it reacted to any of the substances.
Most people return to the doctor again a few days after this. Checking the same areas several times can help your doctor decide if you have allergic or irritant contact dermatitis.
After patch testing, you need to avoid certain activities and medicines. This is to make sure the test results are accurate. Until you have gone to all your follow-up visits:
●Do not shower.
●Try not to sweat – Do not exercise, and try to avoid very hot and humid areas, such as saunas.
●Do not scratch or remove the patches – If you react to any of the substances, your skin might feel itchy and uncomfortable. But it's important not to scratch or remove the patches on your own.
●If the doctor wrote on your skin, do not scrub it off.
What do my results mean? —
If you are allergic to any of the substances, your skin might:
●Get a rash – The rash might look raised and bumpy. In people with light skin, the rash is often red. In people with darker skin, it might appear purple, brown, gray, or black.
●Be itchy
Your doctor will look at your skin and use a scoring system to help figure out what you are allergic to. They will give you these results in the office. If you have any allergies, your doctor will talk to you about how to avoid allergic reactions in the future.
If your doctor cannot tell if you are allergic to any of the substances after patch testing, they will do more tests. These can include:
●Another patch test
●Repeated open application test – This involves putting the substance on an area of skin 2 times a day for up to 28 days or until your skin reacts.
●Usage test – This involves using the substance in your usual routine to see if your skin reacts.
Patient education: Contact dermatitis (The Basics)
Patient education: Eczema (atopic dermatitis) (The Basics)
Patient education: Allergy skin testing (The Basics)
Patient education: Contact dermatitis (including latex dermatitis) (Beyond the Basics)
Patient education: Eczema (atopic dermatitis) (Beyond the Basics)
