Human health is increasingly shaped by the environments in which people live, work, learn, receive care and age

Indoor environments are increasingly recognized as key determinants of human microbial exposure and skin health. Microbiome-aware interventions, including probiotic and prebiotic formulations, have been proposed to complement conventional environmental hygiene. However, quantitative data on the spatial distribution of nebulized prebiotic/postbiotic mixtures in enclosed spaces are lacking. The aim of this exploratory study was to characterize the aerosolization efficiency and spatial deposition of a prebiotic/postbiotic solution nebulized by two different devices in standardized indoor microenvironments. Two nebulizing devices were tested separately in two identical 20′ ISO containers (33.2 m³). A liquid prebiotic/postbiotic mixture at two concentrations (10% and 20% v/v in water) was nebulized for 1 or 2 h. Surface deposition was assessed using passive paper samplers placed at horizontal distances of 0, 25, 50, 100 and 200 cm from the aerosol outlet. A volatile chemical marker contained in the solution was quantified by gas chromatography–mass spectrometry to estimate deposited volume per unit area. Both devices generated detectable marker deposition at all distances, ranging from 0.22 to 14.42 µL·cm⁻² of concentrate equivalent. In a mixed-effects model treating the individual run as the unit of replication, distance was the only factor reaching statistical significance, deposition decreasing approximately twofold per 100 cm (p < 0.001); the apparent effects of device type, concentration and run time did not reach significance. Spatial decay profiles were condition-dependent rather than systematically device-specific. Nebulized prebiotic/postbiotic mixtures can be delivered across meter-scale distances in enclosed indoor settings. Because each condition was tested in a single run, aerosol properties were not characterized and no microbiological or clinical endpoints were assessed; these findings represent a feasibility and exposure-characterization step rather than evidence of biological or health benefit, and they support further investigation of nebulized microbiome-modulating interventions in environmental and occupational medicine.

Indoor Environmental Quality (IEQ) is the standard framework for evaluating how buildings affect occupants, traditionally through air quality, thermal conditions, lighting and acoustics. These domains are indispensable, but large occupant-survey datasets show that measured physical parameters account for only part of the variance in how occupants evaluate and respond to a space, and certified buildings do not consistently outperform conventional ones on occupant-reported outcomes. This Perspective therefore proposes Human Environmental Quality (HEQ): a research framework that retains conventional IEQ as its physical baseline and adds psychological, sensory, restorative, biophilic and social–spatial domains, assessed across five measurement layers ranging from environmental monitoring to population health. HEQ is not a validated index, a certification score or a claim of novelty for “including psychology”—healthy-building frameworks, the salutogenic tradition, evidence-based healthcare design, and the eudaemonic-design and flourishing literatures have argued for human-centred assessment for decades, and we situate HEQ explicitly within that lineage. Its two testable contributions are narrower: the separation of sensory and restorative quality as assessable domains distinct from general satisfaction and from biophilia, and a pre-specified protocol under which each additional domain must demonstrate incremental predictive validity over conventional IEQ before being retained. We give candidate indicators and instruments per domain with an explicit evidence grade, a single-assignment rule with variance-partitioning procedures for overlapping exposures such as daylight, measurement-invariance and pre-registration requirements, and a minimum specification—domains, layers, buildings, design and primary outcome—for a first credible HEQ study. Where a domain cannot meet the incremental-validity standard, the framework should be reduced accordingly.

Building assessment asks what an environment offers its occupants. It rarely asks what the environment requires from them. Yet perceiving, interpreting, navigating and adapting to a space consumes attention, working memory and self-regulatory effort that the occupant’s primary activity also needs. We propose Cognitive Environmental Load (CEL) as the combined perceptual, attentional, spatial–orientational, mnemonic, decisional and social-regulatory demand a setting imposes during use, and Cognitive Environmental Load Design (CELD) as the design position that follows: calibrating that demand against task requirements, available resources, perceived control and opportunities for recovery. CEL is relational rather than a fixed property of space—it emerges from environment, task, person and time together—and CELD is therefore not an argument for minimum stimulation. Complexity that carries information, supports orientation or invites engagement is not a cost. We set out a provisional six-domain taxonomy, candidate design principles, and a measurement agenda that deliberately postpones any composite index until content, construct and discriminant validity have been established. We state what would falsify the construct. CELD is offered as a hypothesis-generating framework requiring empirical validation, not as a metric, rating or design standard.