The human skin microbiome has shown promise for forensic geolocation, yet the environmental factors driving this geographic variation remains poorly understood. Here, we investigated whether local aeromicrobiome contribute to shaping human skin microbiota across diverse urban settings and environmental conditions. By clarifying the ecological basis of geographic variation in skin microbes, this work aims to provide a biological foundation to improve the accuracy and generalizability of future geolocation models. 

We conducted a multi-center study across five Chinese cities and four typical micro-environments, collecting 494 human forehead skin samples for metagenomic sequencing and 22 air samples for absolute and relative quantification of 16S rRNA and ITS. Multi-omics data were integrated with host lifestyle questionnairs and environmental metadata, including meteorological variables and air pollution indics. 

Variance partitioning analysis showed that geographic location explained more variation in skin community structure and antibiotic resistance genes (ARGs) than  host lifestyle factors such as skincare practices and exercise. Across all locations, skin microbiota could be categorized into two baseline ecotypes, termed "nutrient-rich" and "environmental stress". Air sampling further revealed highly localized aeromicrobiomes. Relative quantification captured inter-city taxonomic variations more clearly than absolute quantification, likedly because it reduced interference from unstable atmospheric biomass. Fungal communities showed stronger geographic resolution than bacterial communities, consistent with more localized deposition of larger fungal particles. Environmental association analyses indicated that bacterial variations was primarily linked to air pollution metrics such as O3, PM2.5, PM10, and AQI, while fungal variation was more strongly associated with macro-climate factors such as latitude, humidity, and temperature. Crucially, city-specific skin microbial signatures were strongly correlated with corresponding  city-specific atmospheric microbiota. 

Together, these findings suggest that geographic variation in the skin microbiome is shaped more strongly by local environmental exposure than by individual lifestyle, and that aeromicrobiomes are important contributors to this spatial structuring. This environmentally grounded interpretation provides a stronger biological basis for developing and optimizing forensic geolocation models based on human skin microbiota.

Keywords

Skin microbiome, Aeromicrobiome, Forensic geolocation.

Authors

• Lihuan Zhu (Hebei Medical University, China)
• Guangping Fu (Hebei Medical University, China)
• Jing Han (Hebei Medical University, China)
• Yinxue Liu (Hebei Medical University, China)
• Shuhuan Wang (Hebei Medical University, China)
• Yusi Zhu (Hebei Medical University, China)
• Guanju Ma (Hebei Medical University, China)
• Shujin Li (Hebei Medical University, China)