Contact dermatitis (including irritant dermatitis and allergic contact dermatitis/allergic dermatitis) is a reactive inflammatory skin disease that occurs at the site of contact when the patient’s skin or mucous membranes come into contact with certain external substances, often showing symptoms such as erythema, swelling, intense itching and blistering, and is one of the common diseases in dermatology, accounting for about 10% of all outpatient visits. Dr. Chen Xue, deputy chief physician of the Department of Dermatology and Venereology at Peking University People’s Hospital, pointed out that in addition to treating contact dermatitis with symptomatic medication as soon as possible, finding the cause and identifying the skin allergens is very important to avoid aggravation of the disease and prevent recurrence. Contact dermatitis is caused by a variety of allergens, and many common items can cause skin allergies. Among them, allergies to accessories are easier to identify, such as eyeglass frames, necklaces, watches, rubber products, etc., where the redness and swollen borders are very obvious at the contact location; hair dyes, shampoos, cleansers, various cosmetics and creams are also common allergens, which may cause obvious itchy skin symptoms after use. The most common method for finding contact dermatitis allergens is the patch test, and most hospitals have a primary screening kit. Medical personnel place common contact allergen testing reagents in separate patch test kits and place multiple patch test kits on the patient’s back or upper arm. The formal procedure is to remove the spot test after 48 hours and observe the skin after 30 minutes for itching, erythema, papules, blisters, etc. for the first reading, and then after 24-48 hours for the second reading. This interpretation method requires the patient to be seen a total of 3 times (posting, 48-hour interpretation, and 72-96-hour interpretation). The current clinical practice is that the patient removes the patch after 48 hours, asks a family member to help record the patch after 30 minutes, and then visits the patient after 24 hours to read the skin allergy. It should be noted that some patients develop allergy symptoms much later, so they need to be observed once more after 7 days of patching and ask the doctor to make a judgment if necessary. Dr. Chen added that China’s common patch kit primary screening series includes 20 common contact allergens, while Peking University People’s Hospital can now also test for 40 common allergens on the head and face, which can further prevent the occurrence of contact dermatitis on the head and face. It should be noted that patients in the acute phase of contact dermatitis, such as severe redness and swelling of the skin with blisters and macules, are not suitable for patch testing. If patients are undergoing anti-allergy treatment, they need to be tested after stopping the medication: 2 weeks for patients taking oral glucocorticoids (such as prednisone, methylprednisone, dexamethasone or trenbolone); 3 days for patients taking antihistamines; and 2 weeks for patients taking oral immunosuppressants (including herbal medicines such as tretinoin preparations). For patients treated with physical methods such as phototherapy and radiotherapy, the treatment needs to be stopped for 4 weeks before the patch test. During the patching period, patients should avoid sweating and prevent sun exposure. If the allergic reaction at the patching location is serious, it should be removed promptly and the test should be stopped. In addition to patch test, skin prick test is also a common test method. Medical personnel will be a high concentration of allergen solution drops on the surface of the patient’s skin, with a prick needle lightly stabbed into the skin surface, a few minutes later to observe whether the allergic reaction, this method for the detection of acute urticaria and atopic dermatitis allergens effective. Dr. Chen introduced, there is also a Mora biological testing method, claiming that through two electrodes and patient finger contact, you can immediately get the test results, seemingly convenient and non-invasive, but the credibility is very low. How to take care of contact dermatitis patients in daily life? The patient should first avoid contact with known allergens to prevent recurrence of the disease; secondly, maintain a good skin barrier, bathing should not be too diligent, bath water is too hot, alkaline bathing products or rubbing will destroy the skin barrier, after bathing should immediately apply emollients (hot sweaty season choose moisturizing milk, cold dry season choose moisturizing cream), if soon after applying emollients feel dry and taut skin or white bran-like flaking, indicating that This kind of emollient moisturizing effect is not good, can increase the application frequency or replace the moisturizing ability of better emollient. The majority of contact dermatitis will not recur if you do the above two things.