Imbalances in gut microbiota reportedly contribute to the development of autoimmune diseases, but the association between the etiopathogenesis of alopecia areata (AA) and gut microbial dysbiosis remains unclear. This cross-sectional study was conducted to identify and compare the composition of the gut microbiome in patients affected by AA and those in a healthy control (HC) group, and to investigate possible bacterial biomarkers for the disease. Fecal samples were collected from 19 AA patients and 20 HCs to analyze the relationship with fecal bacteria. The three major genera constituting the gut microbiome of AA patients were Bacteroides, Blautia, and Faecalibacterium. The alpha diversity of the AA group was not statistically significant different from that of the HC group. However, bacterial community composition in the AA group was significantly different from that of HC group according to Jensen–Shannon dissimilarities. In patients with AA, we found an enriched presence of the genera Blautia and Eubacterium_g5 compared to the HC group (p < 0.05), whereas Bacteroides were less prevalent (p < 0.05). The gut microbiota of AA patients was distinct from those of the HC group. Our findings suggest a possible involvement of gut microbiota in in the as-yet-undefined pathogenesis of AA.

Vitiligo is an autoimmune skin disease with a significant psychological burden and complex pathogenesis. While genetic factors contribute approximately 30% to its development, recent evidence suggests a crucial role of the gut microbiome in autoimmune diseases. This study investigated differences in gut microbiome composition and metabolic pathways between active spreading vitiligo patients and healthy controls using shotgun whole-genome sequencing in a Korean cohort. Taxonomic profiling reveals distinct characteristics in microbial community structure, with vitiligo patients showing an imbalanced proportion dominated by Actinomycetota and Bacteroidota. The vitiligo group exhibited significantly reduced abundance of specific species including Faecalibacterium prausnitzii, Faecalibacteriumduncaniae, and Meamonas funiformis, and increased Bifidobacterium bifidum compared to healthy controls. Metabolic pathway analysis identified significant enrichment in O-glycan biosynthesis pathways in vitiligo patients, while healthy controls showed enrichment in riboflavin metabolism and bacterial chemotaxis pathways. These findings provide new insights into the gut–skin axis in vitiligo pathogenesis and suggest potential therapeutic targets through microbiota modulation.