Aung H.W.Kliengchuay W.Niampradit S.Aendo P.Aye T.S.Intrakun S.Arthan D.Koompapong K.Lin T.H.Vardoulakis S.Lung S.C.C.Tantrakarnapa K.Mahidol University2026-04-292026-04-292026-06-01Environmental and Sustainability Indicators Vol.30 (2026)https://repository.li.mahidol.ac.th/handle/123456789/116379Approximately 670 million residents in the ASEAN region face heat-related health risks including synergistic effects with air pollution. Despite health impacts of heat studies existed in individual countries, a regionwide analysis is required for better understanding of the situation and gaps. This scoping review explored the heat related mortality, morbidity and effect modifications with air pollution in Southeast Asian countries. Studies published from 2000 onwards were searched in PubMed, SCOPUS, Wiley Library, and through manual search for relevant studies. A total of 851 studies were screened, and 76 studies included in the review, whereas 28, 38 and 10 studies respectively for mortality, morbidity and effect modification respectively. Regionwide, minimum temperatures observed as 24·32 °C to 30 °C for mortality, and 23·4 °C to 37 °C for morbidity risks. Relative risks ranging from 1·02 for all-causes admissions in Vietnam to 4·21 for dengue incidence in Laos, but variation existed by the area and outcomes. Non-linear relationships, J-shaped and U-shaped for NCDs and intestinal infections, inverse-S shaped and negative association for dengue and Covid-19 observed respectively. Effect modification with air pollution existed but substantial and few studies opposed the findings. Immediate effects were stronger than lagged impacts, particularly for NCDs although delayed effects observed up to 9-10 months for dengue. Extreme ages, people with preexisting diseases especially respiratory disease, outdoor laborers, people from high air polluted and crowded, and rural residents identified as most vulnerable. The review underscores the needs for standardizing heatwaves definitions and extending geographical coverage to formulate the collaborative adaptation strategies.Environmental ScienceAgricultural and Biological SciencesReviewSCOPUS10.1016/j.indic.2026.1012722-s2.0-10503641347926659727