Taxonomic and Functional Skin Microbiome Profiles in Nummular Eczema, Atopic Dermatitis, and Mixed Phenotypes: An Exploratory Shotgun Metagenomic Pilot Study

Nummular eczema (NE) and atopic dermatitis (AD) share clinical features, yet their skin microbiomes remain insufficiently characterized. This exploratory pilot study evaluated the taxonomic composition and functional potential of the skin microbiome across NE, a mixed NE/AD phenotype (Mixed NE_AD), and AD using shotgun metagenomics. Lesional swabs from Korean patients with NE (n = 8), Mixed NE_AD (n = 6), and AD (n = 5) were sequenced to assess microbial diversity, taxonomy, and functional pathways. Staphylococcus aureus predominated across all groups. NE samples were characterized by the higher relative abundance of environmental taxa, wherein Delftia acidovorans was observed only in NE samples in this cohort, and Kocuria palustris diminished sequentially across the Mixed NE_AD and AD phenotypes. Mixed NE_AD exhibited greater intra-genus Staphylococcus diversity. Despite non-significant overall diversity differences, partial ecological separation was noted. Functionally, descriptive differences in metabolic potential were observed, with NE showing trends toward biosynthetic and oxidative stress-associated pathways and AD showing trends toward degradation-related pathways. Mixed NE_AD showed intermediate characteristics. Although these differences did not reach statistical significance after correction for multiple testing, these findings provide preliminary evidence for microbiome-based stratification of eczematous disorders, warranting larger cohort validation.