Patch Testing (TRUE tests)

To help your allergist identify potential causes of your contact dermatitis your allergist might use a patch test to determine potential causes, such as rubber, fragrances or hair dye. Patients are typically asked to wear the patch for 48 hours, keeping it dry for that period. Your allergist will then ask you to return twice — one day after the patches are removed and again a week later — to check on your reaction.