ObjectiveTo investigate the possible mechanism of Pibai Yucuo Formula （枇柏愈痤方， PYF） in treating acne from the perspective of skin barrier damage. MethodsThirty-two mice were randomly divided into blank group， model group， minocycline group， and PYF group， with 8 mice in each group. Except for the blank group， mice were induced by intradermal injection of Cutibacterium acnes （C.acnes） combined with topical application of artificial sebum to establish acne model. The blank group and model group received intragastric administration of 0.2 ml of distilled water， while the PYF group received intragastric administration of 22.75 g/（kg·d）of PYF， and the minocycline group received 0.013 g/（kg·d）of minocycline suspension， all once daily for 5 consecutive days. On day 0 and day 6 of the experiment， the body weight of mice in each group was recorded， and the absolute value of the body weight difference during the experiment was calculated. Skin conditions were assessed with multifunctional skin imaging system on the 2nd， 4th and 6th day of the experiment. Skin barrier function indicators including transepidermal water loss （TEWL）， and the water content of the stratum corneum and epidermis on day 0， 2， 4 and 6 of the experiment. Optical coherence tomography （OCT） was used to observe stratum corneum and skin thickness on the 1st， 3rd and 5th day of the experiment. Hematoxylin-eosin （HE） staining was performed to observe histopathological changes， while ELISA was used to detect interleukin-17A （IL-17A） levels， and immunofluorescence staining was used to assess skin barrier-related proteins filaggrin （FLG） and loricrin （LOR） levels of skin lesions on day 6 of the experiment. ResultsCompared to the blank group， the model group showed a decrease in body weight on day 6， and an increase in the absolute value of the difference in body weight before and after the experiment （P＜0.05）. On day 4 and 6， TEWL values increased， while water content in the skin stratum corneum and epidermis decreased （P＜0.05）， accompanied by elevated IL-17A level and reduced immunofluorescence intensity of FLG and LOR proteins （P＜0.05）. The model group mice showed papules or pustules at the skin modeling site with progressively worsening desquamation under multifunctional skin imaging system. OCT revealed focal epidermal protrusions， blurred epidermal-dermal boundaries， and disorganized structural layers. HE staining showed significant epidermal hyperkeratosis and incomplete keratinization in the skin， with keratin plug formation in hair follicles and glandular lumens， thickened stratum corneum， hyperplasia of the stratum spinosum， as well as dense dermal inflammatory cell infiltration， and capillary dilation. Compared to the model group， both the minocycline group and the PYF group showed a reduced difference in body weight before and after experiment （P＜0.05）. On day 4 and 6， the TEWL value decreased， and water content of the skin stratum corneum increased （P＜0.05）； on day 6， the IL-17A level in the skin lesions decreased and immunofluorescence intensity of FLG and LOR proteins increased （P＜0.05）. On day 4 and 6， the severity of the skin lesions and range of redness and swelling were lighter than those in the model group， with reverted epidermal thickness， smoother surface and clearer epidermis-dermis boundary. HE staining showed that the degree of skin keratinization was reduced， and the inflammatory infiltration and vascular dilation in the dermis were improved compared to the model group. The PYF group showed better results than the minocycline group in reducing TEWL value on day 4 （P＜0.05）. ConclusionPYF may improve inflammation and skin barrier damage by downregulating IL-17A levels in lesion tissue and increasing skin barrier-related proteins， which could be one of the potential mechanism of action on acne.