Patch test: According to the nature of the subject to prepare the appropriate concentration of the dip, solution, ointment or original as a reagent, in an appropriate way will be applied to the skin, after a certain period of time to observe whether the body to its hypersensitivity reaction. The patch test is currently the main clinical method used to detect type IV hypersensitivity reactions. Indications: contact dermatitis, occupational dermatitis, hand eczema, cosmetic dermatitis, etc. Site: Flexor side or back of the forearm. Time: Two weeks after the acute phase, stop taking corticosteroids 1 week before the test, stop taking antihistamines 2 days before the test. Methods: use commercially available spot stickers in small aluminum chambers, add the substance to be tested, remove 24-48 hours after the sticker is applied, observe the skin reaction, and the results are (-) to (++++). Distinguish between irritation reaction or metamorphosis.