Investigating human heat stress: A systematic review of research approaches and methodologies

Heat stress is a complex, multifaceted phenomenon shaped by human physiology, socio-economic conditions, and climatic factors, with far-reaching implications for communities and economic productivity. Despite extensive research across disciplines, the field remains fragmented, with approaches often applied in isolation, resulting in partial and non-comparable understandings. This fragmentation has reinforced the assumption that heat stress can be adequately characterised using a single dominant method, most commonly heat stress indices, with limited guidance on how to select appropriate methods for different research purposes, despite their direct influence on risk assessment and policy relevance. This systematic literature review examines four key approaches namely, heat stress indices, temperature-only, subjective, and mixed methods, by identifying their characteristics, strengths, and limitations. Following PRISMA guidelines, 74 studies were reviewed and comparatively assessed using the IPCC disaster risk framework to evaluate how each approach represents hazard, exposure, and vulnerability. The findings highlight that methodological choices must align with study objectives, data availability, and intended policy outcomes. This review provides a foundation for more coherent and comparable assessments and offers a structured guide for method selection in heat stress research and risk reduction policy while also highlighting pathways for advancing interdisciplinary integration. • There are four main approaches for assessing heat stress among people. • Heat Stress Indices dominate research, followed by mixed-method approaches. • No single approach is universally optimal; each serves distinct research purposes. • The review advocates for context-sensitive and purpose-driven approaches for heat stress assessment.