Designing for Microbial Equity: Reframing "Green" as Opportunity for Beneficial Microbial Exposure

Urban greenspace promotes health, yet a critical mediator-exposure to environmental microbes-is rarely centered in policy or design. This Perspective synthesizes three strands of evidence: (i) contact with nature can modulate the human microbiome and immune markers; (ii) inequities in access to quality, safe, culturally acceptable greenspace are widespread; and (iii) socioeconomic status (SES) is associated with differences in the human microbiome. Together, these strands outline microbial inequality: unequal opportunity to encounter beneficial environmental microbes. Rather than proposing a new index or blueprint, the focus is shifted toward a concise reframing in urban health-from the amount of green to the opportunity for microbial contact, including indoor environments. Near-term research priorities that are feasible without elaborate metrics are also highlighted. This Perspective aims to provide a practical, microbiome-aware basis for design and policy conversations on equity.