Patch Test Information

Instructions for Patch Test Patients

Your doctor believes that your skin problem may be an allergy related to contact with chemicals in your environment. This is called allergic contact dermatitis. The only way to prove an allergic contact dermatitis is by patch testing. This is different from scratch or prick testing and does not identify food or inhaled allergies or allergies to oral medications. Patch testing involves applying a series of carefully chosen chemicals to your skin for a period of 48 hours; the reaction of skin is then assessed at 48 hours and at 96 hours. If you believe that your problem is worsened by any agent or product, even a medication, please bring it with you.

  1. The patches will stay in place for 48 hours (2 days). You will need to keep your back dry at all times until testing is complete (the full 96 hours – 4 days). Moisture will cause the patches to come loose or wash off the ink markings used to mark the location of your tests once the tape is removed. If you normally take showers, baths or sponge baths will need to be substituted. When washing your hair, be careful not to splash water on your back. Avoid excessive activity that will cause perspiration.
  2. It is rare for the patches to become loose. If a strip of the tests should detach so that the metal chambers are not in contact with your skin, DO NOT attempt to replace the patches. This will cause mixing of the chemicals and inaccurate results. Instead, remove the loose strip, noting the day and time. It will also be helpful if you write down any reactions you might notice as the tape is removed. Mark the location of the removed patch with a ball point pen by drawing a rectangle the size of the strip of patches.
  3. You may develop itching under the patches. If the itch is severe or if you develop pain, you should call your doctor. If the doctor is not available, have someone carefully remove only the painful/itchy patch and mark the location of the patch with a ballpoint pen. Try not to disturb the other patches. You may develop blisters at positive sites. It is very rare, though possible, to have prolonged reactions or even scars at sites of severe reactions.
  4. Some patients find it more comfortable to wear a snug T-shirt at night to help keep the patches in place and to absorb any perspiration.
  5. Should you have any questions or problems with your patch tests, please feel free to call the office at 612-873-3500 during the day or 612-873-3000 and ask for the dermatology resident on call during evenings or weekends. Tell the operator who answers the telephone that you are a patch test patient, and explain the problem that you are having with the test.
  6. During the testing period, you should not be taking oral prednisone nor should you have had cortisone injections within a month because this will interfere with the test result. If you are taking prednisone and have been taking it for more than a month, it is very important that you consult your doctor and that you do NOT stop taking the medication suddenly. It is fine to continue using any topical creams or ointments your doctor has ordered, except it should not be applied to the back for one week before the patch testing is to begin. Sunlight, tanning booths or light treatments to the back should be avoided for 2 weeks prior to testing.
  7. If you are unable to keep your return appointments for reading of the tests, please call the Patch Test Coordinator at 612-873-3500 as soon as possible. You will need to be rescheduled for testing at a later date.
  8. Your tests may be completely negative. This probably means that an allergy is not the cause of your skin problem. The test is not infallible, however, and an allergy may have been missed. Retesting in the future may be indicated.