Thermal Sensitivity and Biomarkers as Predictors of Individual Heat-Stress Vulnerability in Indoor Environments

Department of Architectural Engineering, Penn State University, University Park, PA, 16802, USA

^* Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Abstract

Heat-related illness remains a critical public health concern, yet individual vulnerability to heat stress in everyday indoor environments is not well characterized. While prior research has identified physiological thresholds of heat strain and data-driven models have improved prediction of thermal sensation, these approaches often fail to capture heat vulnerability because subjective comfort metrics and physiological responses are rarely integrated. This study investigates thermal tolerance as a physiologically grounded indicator of individual heat-stress vulnerability during sedentary indoor work. Experiments are conducted in a controlled indoor environment with gradually increasing thermal exposure. Subjective thermal tolerance is assessed alongside continuous physiological monitoring, including core and skin temperature, heart rate variability, and electrodermal activity. Results show that thermal tolerance is strongly associated with both environmental heat metrics and physiological regulation. Higher tolerance is associated with greater parasympathetic activity and smaller changes in core and skin temperature, whereas lower tolerance is associated with elevated environmental heat stress and autonomic imbalance. Clear physiological differentiation is observed between bearable and unbearable tolerance states. These findings demonstrate that thermal tolerance integrates subjective perception with physiological heat strain, providing a meaningful indicator of individual heat vulnerability in indoor environments. Combining tolerance-based assessment with wearable physiological sensing supports more reliable monitoring of heat stress and enables adaptive, personalized indoor climate control strategies that improve both comfort and safety.