(Scientific Insights from Carla’s Love School)
Note: This post explains research about how natural environmental exposure (including soil microbes and green play) may support your child’s developing immune system and gut health. It is not an encouragement to feed children large amounts of dirt, but rather to thoughtfully embrace safe, supervised outdoor play and garden experiences.
Your child’s gut microbiome — the community of bacteria and other microbes living in the digestive tract — plays a crucial role in digestion, immune development, metabolism, and even neurodevelopment through the gut-brain axis (Robertson et al., 2019).
During the first 1000 days of life, the microbiome develops rapidly, and early environmental exposures shape long-term immune and metabolic outcomes (Milani et al., 2017; Tamburini et al., 2016).
Disruptions in early microbiome development have been associated with increased risk of asthma, allergies, inflammatory disorders, and metabolic disease (Stiemsma & Michels, 2018). This suggests that microbial diversity in early life supports healthy immune calibration.
Emerging research shows that exposure to biodiverse outdoor environments — including soil, plants, grass, and natural play spaces — can positively influence children’s microbial communities.
A randomized controlled trial in Finnish daycare centers demonstrated that adding forest floor and natural materials to play areas increased children’s skin and gut microbial diversity and improved immune regulatory markers (Roslund et al., 2020).
Similarly, exposure to green space has been associated with differences in gut microbiota composition in children, suggesting that environmental biodiversity may shape internal microbial ecosystems (Selway et al., 2020).
Short-term contact with soil microbes can transfer environmental bacteria to hands and potentially into the oral and gut microbiome through normal exploratory behavior (Robinson et al., 2020).
The “Old Friends” hypothesis proposes that humans evolved alongside a wide range of environmental microbes — particularly soil and plant organisms — that play a role in immune system training (Rook, 2013; updated discussions in Rook et al., 2017).
Reduced exposure to environmental biodiversity in modern urban settings may contribute to rising rates of allergic and autoimmune conditions (Rook et al., 2017).
Recent research supports the “biodiversity hypothesis,” showing that children living in greener environments have lower rates of allergic sensitization and immune dysregulation (Hanski et al., 2012; Roslund et al., 2020; Stein et al., 2016).
In other words, early microbial exposures help the immune system learn tolerance — distinguishing harmless substances from true threats.
Young children explore through touch and mouthing behaviors — this is developmentally normal.
While intentional or excessive geophagy (soil ingestion) is not recommended due to potential contaminants, supervised contact with clean, chemical-free soil in natural environments differs significantly from contaminated urban soil exposure (Robinson et al., 2020).
Studies of farm-raised children consistently show lower rates of asthma and allergies, likely due to higher environmental microbial exposure during early development (Stein et al., 2016).
Moderate, safe interaction with soil and garden ecosystems may therefore contribute to microbial exchange that supports immune resilience.
Safety remains essential:
This is about exposure, not consumption.
Beyond microbiome effects, green outdoor exposure has broader health benefits.
Green space exposure is associated with lower stress markers, improved emotional wellbeing, and reduced behavioral difficulties in children (Engemann et al., 2019; Jimenez et al., 2021).
Outdoor activity also increases physical movement, which independently influences gut microbiota diversity and metabolic health (Estaki et al., 2016).
Sunlight exposure supports vitamin D production, which interacts with immune regulation and gut barrier function (Misra et al., 2021).
Nature exposure, movement, and microbial diversity work synergistically.
Current research suggests that safe, natural outdoor exposure may:
This does not mean encouraging children to eat soil deliberately.
It means embracing safe, biodiverse outdoor play as part of healthy development.
As both a nurse and child development practitioner, I view safe outdoor exposure as:
Sometimes the simplest interventions — grass, soil, sunshine, slow play — are biologically profound.
References
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