Epicutaneous tests are tests used to detect potential contact allergies. These tests are usually performed on the skin of the back. Allergens are applied to the skin and then patches are placed over them. The allergens stay on the skin for 48 hours, then they are removed. This is followed by the first reading of the results, and usually the next day there is a second reading of the results. The test is positive if redness/swelling/blisters appear at the tested site.