Mud, moss and learning: Finland's biodiverse playgrounds boost children's immune development

Finland's two-year study across 43 daycare centers swapped artificial surfaces for natural materials (soil, sand, moss, forest floor) in about 75 children, finding fewer disease-associated skin bacteria like Streptococcus, gut microbiome shifts linked to reduced inflammation, and increased immune-regulating T cells—suggesting daily exposure to environmental microbes may strengthen early immune development.