You should patch test in two places: first, somewhere hidden (should a reaction occur); and second, somewhere close to the area where the product will be applied once it’s been approved for usage. For example, if you’re testing for your face, a great location is the side of your neck or behind your ear. If you’re testing for your elsewhere on your body, try behind your knees, your belly or your upper arms. Once you’ve determined where to patch test, apply a tiny amount to the area. There should be no other products on the skin so that you can properly test this product. Reactions will typically occur with 24 hours but may take up to 72 hours, so we advise waiting until this time has passed.