I. What are the commonly used topical retinoids? The commonly used topical retinoids include all-trans retinoic acid, isotretinoin, tazarotene and adapalene. Mechanism of action: Topical retinoids can significantly inhibit and reduce the number of acne, promote normal keratinization of follicular epithelium and reduce inflammation of hair follicles, and also enhance the permeability of other drugs, which is the basic means of acne maintenance treatment. The following are the precautions for the topical use of retinoic acid 1. These drugs are photosensitive and should be kept in a cool place under shade and sealed. Avoid excessive sunlight during treatment. Also try to avoid taking photosensitive drugs, such as tetracycline, quinolones, sulfonamides and phenothiazines. 2, such drugs also have a certain degree of irritation to normal skin, when using try to avoid contact with eyes, mouth and other mucous membrane parts; with facial dermatitis or rosacea and other skin diseases patients need to be used with caution. Facial skin should not be treated with the seal pack. 3, before applying the drug need to wash the face with warm water, wash off the skin surface oil and cosmetics, so as not to reduce the effectiveness of the drug. 4, at the beginning of the external use of vitamin A acid drugs, sometimes there will be aggravation of the phenomenon of skin lesions, you can consider the gradual method. That is, the beginning of every 2 days with 1, each time after 1 to 2 hours of drug application, and then wash off with water; then every other day 1, until 1 every night; can also choose a small part of the use of retinoic acid drugs, other parts with antibiotics, etc., and later increase the area of drug application every day, so that the patient’s skin gradually adapt to gradually tolerated. 5, in order to alleviate the symptoms of dry skin mucosa, itching discomfort caused by retinoic acid drugs, it is recommended to use retinoic acid cream at night, and use moisturizing emollients or lipid cream cosmetics in the morning. Minimize the number of face washes with soap, also intermittent and alternating medication, and also try to choose low concentration of retinoic acid ointment (e.g. 0.025%). It is recommended not to use drugs and cosmetics with astringent and drying effects at the same time, such as boric acid solution, foundation, shrinkage water, etc. 6.The combined use of retinoic acid drugs and antibiotic creams can improve the efficacy and accelerate the time to improve symptoms. 7.In general, maintenance treatment is needed after acne symptoms have improved for about 6 to 12 months. 8. There is no evidence that topical retinoic acid can be teratogenic after transdermal absorption, but from a safety point of view, most doctors recommend that it should be used with caution in pregnant, lactating, and childbearing women. 9. Topical retinoids can not only treat acne, but also remove pigmentation, prevent scar formation, and prevent photoaging, but they must be combined with emollients, shading agents, depigmentants, and other drugs.