Patch Test: What Is It For?
In dermatology, patch testing is a diagnostic tool for people with contact dermatitis. Doctors use a patch test to determine whether a particular substance causes or aggravates their condition.
The steps in a patch test varies, but generally, it involves tiny amounts of numerous materials individually placed in a plastic square or round aluminum chamber. The materials are then placed on the patient’s back, secured by a huge adhesive tape.
At the second appointment (usually after 2 days), the dermatologist would remove the patch, and, using a pen with indelible ink, mark the skin for any notable findings. The final look for any reaction usually occurs at the third appointment, which is typically 4 days after the application.
Now, patch testing a new skincare product has almost the same procedures. However, you can do it at home, and it usually only takes 24 hours.