Patch testing is utilized to identify the causes of contact dermatitis which is a reaction to a particular substance such as poison ivy. This condition is not an actual allergy, thus patch testing is carried out in a different manner than allergy skin testing. Remember that there are no allergic antibodies when it comes to contact dermatitis, instead several white blood cells enter the skin which triggers a reaction.
Prior to patch testing, the individual is instructed to avoid using certain medications or using a tanning bed particularly on the back. Take note that the back is the ideal area where the test is performed.
How patch testing is executed
Several allergens are applied to patches that are taped into the skin with a different allergen on every patch. The difference with allergy skin testing is that this test does not involve any needles.
Every patch is applied on clean skin on the back of the individual and left in place for 48 hours. During this period, the individual has to avoid getting the tape of the patch wet, thus no baths or showers and excessive sweating must be avoided.
After 48 hours is reached, the individual has to return to the clinic for removal. Prior to the removal of the patches, the location of every patch is marked using a surgical marker in case further testing is needed.
When the patches are removed, the individual can bathe normally but must avoid scrubbing the back to prevent the removal of the ink markings. The final assessment of the test results is done at 72-96 hours after the first placement of the patch test. This is the time when the individual can bathe as normal.
What are the possible side effects?
Since the objective of patch testing is to determine an allergic reaction, at least a single patch will trigger a localized area of contact dermatitis. If the test turns out positive, it shows bumps, redness, mild swelling or even a small-sized blister.
Since contact dermatitis involves the immune system, patch testing can trigger a memory response. This simply means that the immune system recalls where it encountered a chemical in which the skin reacted. The area of skin that reacted to the chemical can turn itchy and red after the same chemical was applied utilizing patch testing, even though the patch was applied in a different part of the skin. A memory response is a good indication that the offending chemical is identified.
Once all the readings of the patch testing have been completed, the individual can utilize a topical steroid cream on the back to minimize the itchiness and rash. Even though it might cause a few days of discomfort, it is vital for the individual to wait until the final reading of the test has been finished before treating the areas using any creams.
A topical steroid or other prescription anti-itch creams can also be utilized on the area that has a memory response, even during an ongoing patch test. Remember that only the skin where the patch test was applied affects the outcome of the test.