Dynamics of facial skin microbiota in female college students during menstruation: comparative analysis between regular and irregular menstrual cycles with identification of phase-specific microbiota.

Previous studies demonstrate that many women experience menstrual cycle-related skin symptoms during their periods. While the exacerbation of skin conditions during menstruation is well-documented, the underlying biological mechanisms remain incompletely understood. Although an association between skin microbiota and the menstrual cycle have been proposed, to gain clearer insights into this change, we finally enrolled 95 subjects and implemented one-to-one matching in the present study. Facial skin microbial samples were collected from female college students during both menstrual and intermenstrual periods, followed by 16 S rRNA gene sequencing. The facial skin microbiome shifted with menstrual cycle regularity, primarily driven by the irregular menstrual group. Proteobacteria predominated over Firmicutes, Actinobacteria, and Bacteroidetes across all samples. At the genus level, Sphingomonas, Bradyrhizobium, Streptococcus, and Corynebacterium were most abundant. However, Firmicutes and Actinobacteria increased significantly in the irregular menstrual group, with Acinetobacter, Haemophilus, Streptococcus, and Corynebacterium exhibiting peak abundance in this group. Multiclass random forest analysis distinguished irregular menstrual samples from all others, achieving an area under the curve (AUC) of 0.82 using bacterial OTUs; Aeromonas caviae (OTU_423025) and Sphingomonadaceae (OTU_4391560) were identified as the model's most important OTUs. Reduced intra-kingdom interactions were observed in subjects with irregular cycles. Notably, in the irregular menstrual group, three co-occurring OTUs including Streptococcus (OTU_523025), Gemellaceae (OTU_858896), and Staphylococcus (OTU_4345285) were lost. Furthermore, PICRUSt2 analysis predicted upregulation of genes involved in fatty acid, carbohydrate metabolism and signal transduction (e.g., K01462, K01104, K17686) and downregulation of transport (K01991) and antioxidant related genes (K00799) in the irregular menstrual cycle group. The study indicates that irregular menstruation is accompanied by alterations in the structure of the skin microbial community, with such structural changes primarily occurring during the menstrual phase. Additionally, distinctive features of the facial skin microbiota were observed in the Irregular-Menstrual group.