Medical Dermatology > Patch Testing
What is patch testing?
Patch testing identifies substances that cause persistent skin rashes. People often develop allergies to ingredients in skin care products, cosmetics, or topical medications. Chemicals and dyes in clothing, rubber and leather components in shoes and gym equipment, jewelry and metals can also be responsible for skin reactions. When these substances contact the skin, they may result in a rash known as contact dermatitis. This allergic reaction can manifest itself in many ways: itch and redness, swollen eyelids, dry hands and many others. Once the culprit substance (allergen) is identified, the rash significantly improves with avoidance of that substance.
Patch tests are distinct from skin prick tests, which are used to diagnose hay fever and other internal allergic reactions. Skin prick tests have limited value for patients with skin rashes.
How is patch testing performed?
Patch testing involves a series of appointments, each lasting approximately 30 minutes. Three appointments will be scheduled during the span of one week on a Monday, Wednesday and Thursday.
Monday: A member of our health care team will place adhesive strips on your back and upper arms. Tiny quantities of up to 150 allergens in individual square aluminum chambers will be applied and secured with adhesive tape. You may reinforce loose patches with tape at home if necessary.
Wednesday: You will return for removal of the adhesive strips and an examination for reactions such as redness, inflammation and swelling at the site of patch application.
Thursday: The patch test sites will be examined again. Dr. Norden will discuss the significance of both positive and negative results and you will be given information about the substances that cause the skin reaction. You will also receive a printout from the American Contact Dermatitis Society Contact Allergen Replacement Database (CARD) outlining products you can safely use.
If a new, positive reaction (localized rash or itchy spot on the back or arms where tested) is noted within a week or two after patch testing, you should notify the office. Please note that some reactions may stay positive for weeks.
Can any medications interfere with patch testing?
- It is important that you not be taking oral corticosteroids, such as prednisone, or other oral immunosuppressants within one week of patch testing. You should not be patch tested within one month of a cortisone (prednisone) injection.
- It is crucial that you avoid applying steroid/cortisone creams to your back or upper arms within one week prior to patch testing. All topical products, including Vaseline, lotions, creams and ointments, should be avoided 24 hours before patches are applied. Please shower the morning of your first appointment as you will not be allowed to take a bath or shower during the 4 days of testing.
- You may continue to take over the counter or prescription antihistamines such as Benadryl and Claritin.
What should I bring to the Patch Testing appointment?
- It is important you bring any items from home or work that you suspect may be causing your dermatitis. This includes cosmetics, lotions, creams, medications, plants or articles of clothing.
- Please wear loose fitting clothing that is easy to take off and on, such as a button down shirt. Tape strips will be marked with a purple or black marker. This marker may stain clothing, so please dress accordingly.
Are there any side effects, risks, or limitations I should be aware of?
- It is important to avoid strenuous exercise that may loosen the patches or cause sweating during the patch testing week.
- Sun exposure to the testing area should be avoided for 4 weeks prior to your appointments.
- No showering is allowed during the patch testing. Sponge baths are permitted in areas not taped (the lower body, underarms, etc.)
- Patch testing should not be performed if you are pregnant or breastfeeding.