Skin Microbiota Diversity Is Associated with Biophysical Properties Across Healthy Human Skin Types

The skin microbiota plays a key role in maintaining cutaneous homeostasis; however, microbial differences among physiological skin types within healthy individuals remain unclear. In this study, we investigated the association between skin microbiota diversity and four skin types (normal, oily, dry, and combination) in healthy young women (n = 43), with samples collected from the nasal region. Skin moisture and sebum levels were quantitatively measured, and microbiota profiles were analyzed using 16S rRNA gene amplicon sequencing targeting the V3-V4 regions. Normal skin exhibited higher alpha diversity, including Chao1 richness and Faith's phylogenetic diversity, compared with other skin types (median Chao1 values were higher in normal skin than in other groups). Correlation analyses showed that skin moisture was positively associated with microbial richness (ρ = 0.397, p = 0.008), whereas sebum levels were negatively associated with phylogenetic diversity (ρ = -0.455, p = 0.002). Beta diversity analysis revealed that normal skin harbored a distinct microbial community structure. In addition, several bacterial genera were enriched in normal skin, whereas Enterobacterales were observed to be more abundant in non-normal skin types. These findings suggest that skin biophysical properties are associated with microbial community structure and diversity within healthy individuals, although the functional implications of these differences remain to be elucidated.