1, dermatitis in the acute stage should not do patch test, patients should do patch test after two weeks after the dermatitis has completely subsided. 2.If a strong reaction occurs, the patch test can be removed from the body at any time. 3.Patients should not take internal corticosteroids (prednisone 15mg/day can inhibit the reaction of patch test) two weeks before and during the test, and stop using antihistamines two days before and during the test. 4.Do not take bath, drink alcohol and scratch the patch site during the patch test. 5, should keep the patch test material on the skin for 48 hours, try not to remove the patch test material prematurely, the test site should be marked, account for the paste must be airtight, in order to avoid false positive results. If necessary, (such as highly suspected allergic to the allergen and 72 hours positive), the second observation should be made 72 hours after the patch test, and the third observation or repeat test should be made on the 7th day after the patch.