2026 / Forest, Health and well-being, Olfaction, Urban

Associations of Forest vs. Urban Environmental Exposure With Well-Being and Nasal Microbiome Composition: An Exploratory Pilot Study

Citation

Lashus, D. C., Gomez, A., Hummel, T., Jacobs, L. F., Majid, A., Raju, R. M., … & Bratman, G. N. (2025). Associations of forest vs. urban environmental exposure with well-being and nasal microbiome composition: An exploratory pilot study. Environmental Research, 123582. doi.org/10.1016/j.envres.2025.123582

Link to file

A young adult walking in the forest with a walking stickThis study explored how spending time in nature might affect the bacteria in our noses and our well-being. In 2024, researchers studied 13 University of Washington students over 8 weeks. After spending the academic year in Seattle, one group moved to a remote forest in Washington, while the other stayed in the city. Researchers looked at changes in mood, stress, and overall mental health by having participants fill out surveys before and after the exposure. They also collected nasal bacteria samples.

The results showed that the students who spent time in the forest had a bigger improvement in mood, with more positive feelings and less stress compared to those who stayed in the city. When examining the nasal bacteria, researchers found that the forest group showed more diversity in their nasal microbiome after spending time in nature. This included an increase in certain types of bacteria that are linked to better well-being, like Bifidobacterium and Akkermansia.

The study suggests that spending time in nature could help improve mental health by changing the bacteria in our noses. More research is needed to understand exactly how this works.

Abstract

Highlights

  • An 8-week forest vs. urban exposure was associated with affective improvements.
  • Greater post-exposure richness in forest vs. urban group’s nasal microbiomes.
  • Forest group’s nasal microbiome enriched with well-being-associated bacteria.
  • Increased nasal bacterial richness correlated with affective improvements.
  • Bifidobacterium and Akkermansia abundance correlated with affective improvements.

The benefits of nature exposure for human well-being are well-recognized, yet much remains to be understood about the underlying causal mechanisms. This exploratory, hypothesis-generating pilot study used a natural experimental design with University of Washington students (Seattle, WA, USA; 2024) to investigate links between the nasal microbiome and well-being over an 8-week forest vs. urban environment exposure. After an academic year (September-May) during which all participants (N = 13) were full-time students in Seattle, one group relocated to remote forest sites in western Washington (n = 5; forest condition), while another group remained in urban Seattle (n = 8; urban condition). Self-reported affect, rumination, and mental well-being were assessed pre- and post-exposure using validated surveys, and nasal swabs were collected pre- and post-exposure for nasal microbiome profiling via 16S rRNA gene sequencing. Compared to the urban group, the forest group exhibited significantly greater increases in positive affect and decreases in negative affect and rumination. While no between-group differences in overall nasal bacterial community composition were detected pre-exposure, significant differences emerged post-exposure. Moreover, the forest group exhibited greater post-exposure taxonomic richness at a marginally statistically significant level and significant enrichment of taxa previously associated with well-being (e.g., Bifidobacterium, Akkermansia), changes not observed in the urban group. Increases in taxonomic richness and the relative abundance of these key taxa were significantly associated with affective improvements. These preliminary results suggest that nasal microbiome-mediated pathways linking nature exposure with well-being merit further investigation.