Allergic contact dermatitis occurs when your skin comes into contact with a substance that causes you to have a reaction. Patch testing is designed to identify substances that may be causing your skin rash.
During patch testing, substances to which you may be allergic are applied to your back. Your skin is then examined for allergic reactions. Patch testing does not involve scratches or pricks to the skin. It does not identify allergies to food, oral medications, or inhaled substances.
How Do I Prepare for Patch Testing?
If you have taken any oral, nasal, or injectable steroids in the last month please tell your health-care provider. You may use any prescribed skin creams as directed until one week before patch testing. At that time, stop applying prescribed creams to your back (you may continue to apply them to other areas).
You may continue to use moisturizers until the patch-test strips are applied. Avoid exposure to the sun or ultraviolet light (such as tanning booths) for four weeks before patch testing.
If you have hair on your back it will need to be shaved off the night before your first patch test appointment, as it could cause the patches not to lay flush on the skin.
On the day you are scheduled to have your patches applied, you may wish to wear clothes you won’t mind getting stained. On rare occasions, the pen used to mark the area to be tested can stain clothing.
How is Patch Testing Done?
Patch testing involves a series of appointments, each lasting about 20 minutes. These appointments will be scheduled with the patch test nurse.
- Day 1 – Monday
During your first appointment, a nurse will apply seven patches to your back. Each patch contains 10 dime-sized chambers. Each chamber contains a different substance to which you may be allergic. Additional tape may be used to hold strips in place. (Occasionally, the patches are applied to another area of the body.) Once these patches are in place you will not be able to shower, and no vigorous exercise for 48 hours. You can sponge bathe and wash your hair in the sink.
- Day 3 – Wednesday
After about 48 hours, you will return to have the patches removed. Tell the nurse if you experienced any itching or burning when the patches were in place. We do not read the test on this day due to possible irritation from the patches. Once you leave this appointment you can shower normally. Take precaution not to scrub the back or apply any products to the patch test area.
- Day 4 – Thursday
After about 72 hours, you will return for an examination, which is your first patch test reading. Your markings on the back will be reinforced with a marker, and you will be instructed on how to reinforce these at home over the next week.
- Day 11- Thursday
You will return this day for your final patch test reading. We read it this far out as to not miss any delayed reaction you may experience. Once this final reading is done all of the data will be compiled and you will receive a list of allergens you showed a positive reaction to and where they may commonly be found. You will also receive a fairly extensive safe list with products and the names of the manufacturers. These products will not contain any of the allergens you have shown a positive reaction to. You will not get this packet at this visit. You will be contacted in approximately 48 hours when it is ready, and you will have the option to pick it up at the office or have it mailed to you. When you receive your information packet you will be responsible for going through it and finding out what products you are using that may be causing your reactions.
What do my Results Mean?
Positive Results — If patch testing reveals you are allergic to a substance or substances, the test is “positive.” You will be given information about the substance or substances that caused your skin to react, including alternate names for them and the products in which they may be found. Examining the products you use can help you avoid substances to which you are allergic.
Remember: even if you have a positive result, it can be hard to determine exactly what product is causing your reaction and whether other factors also are involved. It may take time to lessen or eliminate your symptoms. Be patient and continue to work with your health-care provider to determine the best ways to manage your condition.
Negative Results — If your skin shows no reaction to patch testing, your results are negative. This may occur when an allergy is not the cause of your skin problems or when the exact chemical causing the problem has not been tested. Retesting of additional chemicals is sometimes needed.
Side Effects and Risks
Although patch testing can cause a reaction at the patch-test site, the test has very few risks or side effects. You may have itching at the patch-test site after testing is completed, but this typically goes away within a few days. Contact your health-care provider promptly if a disk causes intense itching, burning, or pain.