The relationship between outdoor thermal environment, individual thermal exposure, and chest skin temperature: A field study in real-life conditions

Environmental epidemiology traditionally relies on outdoor parameters to assess individual thermal exposure, despite individuals spending most of their time indoors. To quantitatively analyze the relationships among outdoor thermal environments, individual thermal exposure and chest skin temperature, we conducted a field study (n = 99), combining individual thermal monitoring with ERA5-Land reanalysis data. Linear regression and mixed-effects models were used to evaluate the environmental and human factors influencing thermal exposure and physiological responses. Participants (average age 53.1 years) spent over 80 % of their time indoors. Outdoor temperature and relative humidity (RH) were positively correlated with individual exposure parameters (r = 0.84 and r = 0.64 for temperature and RH, p < 0.01), but had limited explanatory power, especially in summer. Significant inter-individual differences existed in individual exposure temperature and RH. Age was significantly positively correlated with individual exposure temperature (p = 0.024), and sex had a significant influence on individual exposure RH (p < 0.01). Chest skin temperature also showed high variability relative to outdoor and personal exposure temperatures. These results indicate that relying solely on outdoor thermal environment parameters to characterize individual thermal exposure has limited validity and is insufficient. To enhance the accuracy of thermal exposure assessments, there is a need to integrate individual-level monitoring data and individual-specific characteristics into evaluation frameworks. This study contributes to advancing the understanding of thermal exposure dynamics in the Chinese population, expanding existing datasets, and highlights the indispensable role of indoor thermal environments in environmental health related studies and policy-making aimed at improving residents’ well-being.