In modern cities, our homes are sealed boxes, climate-controlled, scrubbed clean, and largely isolated from the microbial richness of the natural world. Though this cleanliness may seem safe, scientists are becoming more concerned that lower exposure to environmental microbes is weakening our immune systems. This could raise the risk of asthma, allergies, and inflammatory diseases.
Researchers led by the Finnish Institute for Health and Welfare and the University of Eastern Finland decided to try a simple but radical idea: what if we bring forest microbes back into urban homes?
When Finnish homes had forest soil on their floors, they developed an indoor microbiome more like outdoor microbes and less like human-associated microbes. The findings, the study suggests, mean that simple, even accidental, interventions could, in the future, help rebalance home microbiomes and improve overall health. This is especially true in urban areas where people are less exposed to microbes found in nature.
Lead author, Chief Researcher Martin Täubel said, “Applying forest soil onto a rug led to a clear rise in forest soil‑associated bacteria in the air. The effect was most pronounced at infant breathing height for the first two weeks after application, and the signal was also detectable in other areas of the home.”
Because infants and toddlers spend most of their time indoors, microbes in the home environment are a major source of exposure that helps train their immune systems and can thus impact long-term health. In cities, lower exposure to environmental microbes has been suggested as a risk factor for asthma, allergies, and other inflammatory diseases. There is a growing interest in ways to improve indoor microbial exposure in the quest for healthier interactions.
In this study, the researchers investigated one such tactic: a simple intervention that involved putting forest earth on carpets in the doorsteps of Finnish homes to migrate environmental microbiota inside. The participants were six households from Finland that took part in a 20-week study.
Researchers took dust samples from infant breathing zones (IBZs), adult breathing zones (ABZs), and floors in the homes. They followed bacterial and fungal communities over time using advanced genetic tools (qPCR & amplicon sequencing).
The intervention was remarkably simple: forest soil was repeatedly sown onto rugs in the entryway. These rugs acted like microbial “gateways,” circulating soil-associated bacteria indoors.
The relative abundance of soil bacteria in house dust increased significantly after each seeding. The greatest impact was noted in airborne dust in rug-soil zones and in infants’ breathing zones within two weeks of the interventions.
Bacterial diversity rose, as did an “asthma-protective microbiota index.” At the same time, the fraction of human-source bacteria decreased. The largest microbial change came from a home with no pets, little occupancy, and mechanical ventilation, so conditions that would bring very little natural influx of microbes.
University Researcher Pirkka Kirjavainen said, “It was promising to see that microbial exposure signatures associated with a lower asthma risk may be increased in urban homes with such a simple, low‑cost intervention. The next step is to see whether this type of intervention translates into the health benefits we expect.”
This study shows that a simple soil-to-rug intervention can alter the microbial community in urban homes. Researchers hope that flooding indoor air with beneficial environmental bacteria can restore at least some of the immune-regulating exposures lost to modern lifestyles.
This is particularly important for infant children, whose developing immune systems are sensitive to microbial exposures early in life. Health-promoting microbes targeted to infant breathing zones could someday serve as a preventive strategy against asthma and allergies.
While promising, the findings still need further investigation, the researchers warned. However, the appropriate ‘dose’ and composition of microbial additions require further study to ensure consistent health benefits. Still, the idea is revolutionary: rather than just fighting microbes in our homes, we might learn to cultivate them for health.
Journal Reference:
Täubel, M., Hill, M.S., Allard, S. et al. Environmental microbiota transfer from forest soil into urban homes: a proof-of-principle study. Microbiome 14, 95 (2026). DOI: 10.1186/s40168-026-02352-6
