Exposure to green space is associated with higher skin microbiota species richness in children

Skin is the exterior interface of the human body with the environment and harbors millions of microorganisms crucial for skin health. Associations between early-life green space exposure and the skin microbiome of children remain unstudied. Skin swabs were collected from 402 children (4-12 years old) enrolled in the ENVIRONAGE birth cohort. Skin alpha diversity indices and the relative abundance at family and species levels were determined using 16S rRNA gene HiFi amplicon sequencing. Total green, high-growing green, and low-growing green were estimated in several radii around their current residential and school address based on high-resolution land cover data. Multiple linear regression models between green-space indices and skin microbiome alpha diversity indices were adjusted for sex, age, frequency of soap use, maternal education, season of skin swab collection, sequencing batch, and storage duration of the skin swab. As interaction terms between green-space indices and season were borderline statistically significant, we also ran the linear regression models stratified by season. Last, we performed a differential relative abundance analysis, accounting for the covariables above. Total green and high-growing green in multiple radii (from 100 to 500 m) were positively associated with observed richness (regression coefficients ranging from 10.06 to 15.31 [P-value ranging from 0.03 to 0.12] per interquartile range increase in green). The associations were only statistically significant when skin swabs were collected in the warm season. The relative abundance of the bacterial families Xanthomonadaceae, Intrasporangiaceae, Pseudomonadaceae, and Caulobacteraceae was statistically significantly positively associated with total and high-growing green within 300 m. Our findings suggest an influential role of early-life green space exposure on skin microbiome composition. Additional research is needed to investigate whether the observed positive relationship between green space and skin bacterial richness has implications for human health.