Allergic contact dermatitis is a rash that occurs when a person is allergic to a particular chemical that comes into contact with their skin.
Patch testing is a procedure that is performed to determine if a person’s rash is allergic contact dermatitis versus another type of rash. Patch testing takes 4-5 days to completely. Patches are applied on a Monday. Usually 8 patches (each containing 10 allergens) are placed on the back (or upper arms) with hypoallergenic tape. On Wednesday, the patches are removed and the initial patch test reading is performed. On Thursday or Friday the final patch test reading is performed and the provider details the treatment plan to the patient.
Before patch test application, it is important not to apply cream, lotion, powder, cologne, etc to the location where the patches are applied. During the patch test week, the area of the body where the patches are applied cannot get wet (so that means no working out or showering- although a “sponge bath” is okay). Itching/Burning at the patch test sites is common. Antihistamines such as Benadryl (warning: causes drowsiness), Allegra, Zyrtec and Claritin can help alleviate the itch. Prior to the patch test week, it is important to note that patients cannot have received a cortisone injection within 1 month, oral prednisone within 2 weeks and topical steroids within 1 week (only applies to the site where the patches are applied). Excessive UV exposure should also be avoided 2 weeks prior to patch testing
For more information about contact dermatitis visit American Contact Dermatitis Society.