The disordered skin microbiome has been reported to contribute to the pathogenesis of acne vulgaris, for which benzoyl peroxide (BPO) has long been recommended as the first-line therapy. However, there are no data regarding the effect of BPO treatment on skin microbiota and the epidermal barrier in young adults with acne vulgaris.Thirty-three patients with acne vulgaris and 19 healthy controls were enrolled in the study. All patients received topical treatment with BPO 5% gel for 12 weeks. The epidermal barrier was analyzed at baseline and after treatment. Microbial diversity was analyzed using a high-throughput sequencing approach targeting the V3-V4 region of 16S rRNA genes. After receiving treatment with BPO, patients had significant improvement in their Global Acne Grading System (GAGS) score, porphyrin, and red areas (p < 0.05), and the presence of sebum, stratum corneum hydration (SCH), and transepidermal water loss (TEWL) increased (p < 0.05). When compared with baseline, microbial diversity was significantly reduced after treatment, as calculated by the goods coverage (p = 0.0017), Shannon (p = 0.0094), and Simpson (p = 0.0017) diversity indices. The prevalence of the genus Cutibacterium (before treatment: 5.64 [3.50, 7.78] vs. after treatment: 2.43 [1.81, 3.05], p = 0.011) was significantly reduced after treatment while Staphylococcus (before treatment: 43.80 [36.62, 50.98] vs. after treatment: 53.38 [44.88, 61.87], p = 0.075) tended to increase. The abundance of Staphylococcus was negatively associated with SCH (p = 0.008, r = À0.286). Despite its contribution to an improved GAGS score, BPO treatment for acne vulgaris may reduce microbial diversity and damage the epidermal barrier. K E Y W O R D S acne vulgaris, benzoyl peroxide, epidermal barrier | INTRODUCTIONAcne vulgaris is a highly prevalent chronic inflammatory skin disease involving sebaceous glands, where the altered skin microbiome is thought to play an important role. 1 As a common economically burdensome condition, it affects 44%-95% of adolescents and young adults around the world, of which 80%-85% cases are mild to moderate. 2,3 Benzoyl peroxide (BPO) has long been thought to be a common and effective topical therapy for mild to moderate acne and is highly recommended as a first-line treatment. 4,5 Besides its primary bactericidal effect on Cutibacterium acnes, BPO has mild anti-inflammatory and comedolytic properties. 6,7 Recently, the influence of BPO treatment on the balance of the skin microbiota in preadolescent acne has Xia Xiong and Yongqiong Deng contributed equally to this work.

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