1, the importance of maintenance treatment: After the end of a course of systemic application of isotretinoin and antibiotics, in the case of improvement of acne symptoms in the acute phase (improvement rate > 90%), maintenance treatment should be considered as much as possible to prevent relapse, because all current treatments for acne only inhibit its pathogenesis, rather than cure acne. Therefore, it is necessary to administer maintenance therapy after treatment. After the initial systemic treatment is completed, topical retinoic acid is the main method of maintenance therapy, and when there is inflammatory damage, a combination of peroxynivalenol may be considered. 2. The need for maintenance therapy: ① Microcomedones are the early pathological process of all acne damage; ② The process of microcomedone formation remains permanent and persistent after acne clearance; ③ Avoiding the formation of microcomedones has an acne prevention effect; ④ The main mechanism of action of retinoic acid is to interfere with the pathological process of microcomedones. 3 .Maintenance regimen: ① Topical topical retinoic acid: Topical topical retinoic acid is the main choice for maintenance treatment; ② Duration of maintenance treatment:6-12 months; ③ Peroxymethylphenidate: Combined with topical retinoic acid can reduce resistance after antibiotic treatment; ④ Choice of 2nd line treatment drugs: azelaic acid and salicylic acid.