Skin bacterial community dynamics of hands and forearms before and after military field exercise
The human skin microbiome is crucial for skin health and immunity, especially in the context of extreme conditions faced by military personnel. Soldiers encounter unique stressors and hygienic challenges that can impact the microbial composition of their skin during field exercises and in regular occupational settings. In this study, we aimed to investigate the impact of a military field exercise on the diversity and composition of the skin bacterial microbiota using 16S rRNA sequencing. We conducted a longitudinal study during the NATO exercise Cold Response 2022, involving Norwegian soldiers (n = 19) engaged in outdoor training operations. Skin swabs were taken from soldiers hands and forearms directly before and after the 10-day winter field exercise, and following a 3-week post-exercise leave. Our results reveal hand and forearm-specific shifts in bacterial populations associated with the exercise, likely influenced by environmental exposure, reduced hygiene, and heightened social contact. Alpha diversity increased on forearms while remaining stable on hands, which appeared more resilient to perturbations. Both sites exhibited temporal changes in composition, with soil- and water-associated bacteria enriched post-exercise; most being transient on hands but more sustained on forearms. The soldiers microbiomes became more similar during the exercise, followed by divergence in the leave period. Neither skin site returned to original composition at follow-up, indicating that field exercises may have lasting effects on the microbiome. Our findings highlight the impact of outdoor exposure on microbial communities and suggest that resilience and stability differ between skin sites. ImportanceOptimizing soldier health and resilience is critical for maintaining military readiness and operational effectiveness. The skin, as the bodys first line of defense, is subjected to numerous challenges in military environments. Unique environmental and hygiene challenges can disrupt the skin microbiome and increase susceptibility to skin and soft tissue infections. This longitudinal research provides valuable insights into the effects of military service on the bacterial dynamics of the skin microbiome, but can also inform hygiene management and disease prevention in comparable situations.