The appearance of the skin is observed, and the skin is normal if it is not damaged and shiny. If the skin is suspected to be allergic to a certain allergen, it is necessary to do a specific skin scratch test, which is usually done by disinfecting the skin on the outside of the upper arm or the back and then using a needle tip to scratch a 0.5-1 cm long strip on the skin, so as not to bleed, and then putting a drop of the test substance on it and rubbing it lightly. When multiple allergens are used for the test at the same time, there should be a distance of 4-5cm between the scratches, and the results should be observed 20 minutes after the test, and the test substance should be wiped away and washed. Reaction criteria are as follows: Normal: negative (-) ±, suspicious, edematous erythema or wind mass less than O.5 cm in diameter +, weak positive, wind mass with redness, diameter equal to 0.5 cm ++, medium positive, wind mass with obvious redness, diameter O.5-1.0 cm, no pseudopod +++, strong positive, wind mass with significant redness and pseudopod, diameter greater than 1 cm.