Asia's Silent Killer: Extreme Heat Emerges as Underestimated Health Crisis

Romuel Delos Santos works in the brutal heat of Metro Manila's construction sites, bending and installing steel bars under the Philippine sun. At 27, he has spent the past year doing this work, building on four years of prior experience in the sector. Last year, after prolonged exposure to extreme temperatures, he developed heat rashes and persistent headaches—symptoms that have become harder to manage as the years pass. He now drinks more water and seeks shade whenever possible, but even these precautions feel increasingly inadequate. "I used to be able to endure the hot weather by wearing long-sleeved shirts, but now the heat just seeps through my clothing," he said. "The heat has gotten so much worse over the years. We can really feel the changes in the weather."

Delos Santos is one of millions across Asia confronting a crisis that remains largely invisible in official statistics. While climate change dominates headlines through images of floods, typhoons, and rising seas, extreme heat is quietly becoming one of the region's most dangerous health threats—and one of its most systematically undercounted. Last year, Asia experienced one of its warmest years on record, with ocean temperatures reaching unprecedented levels. The World Meteorological Organization warned that heat is now intensifying multi-hazard risks across the region, placing new pressures on health systems, food production, and livelihoods.

The 2024 heatwave across Southeast Asia made the danger concrete. Thailand confirmed at least 30 deaths directly attributable to heat-related causes. The Philippines recorded 77 cases of heat-related illness, including fatalities. Vietnam declared a state of emergency as abnormally high temperatures triggered severe drought that disrupted agriculture across key producing regions, including parts of the Mekong Delta. Schools and workplaces closed. Power grids strained under demand for cooling. Crops withered. Yet these numbers, alarming as they are, capture only a fraction of heat's true toll.

The reason lies in how deaths are counted. Unlike drowning in a flood or injury from a typhoon, heat-related mortality leaves no visible wound. When someone dies during extreme heat, the immediate cause recorded in hospital systems is often a heart attack, stroke, kidney failure, or respiratory collapse—not heat itself. Juthamard Surapongchai, a researcher at Mahidol University's Gatorade Sports Science Institute in Thailand, explained the consequence: "These deaths are typically recorded within healthcare systems under medical causes such as heart attack or stroke, rather than being classified as disaster-related deaths. As a result, the true mortality burden of heat is substantially underestimated in disaster statistics." Heat exacerbates underlying cardiovascular, renal, and respiratory conditions, killing indirectly. Disaster databases, designed to capture acute trauma from sudden events, miss these slow-motion fatalities entirely. Jemilah Mahmood, executive director of the Sunway Centre for Planetary Health at Sunway University Malaysia, put it plainly: extreme heat is "very likely to rival or even exceed the death toll from typhoons, but it remains largely invisible in the statistics."

The human cost falls hardest on those with the least protection. Delos Santos cannot afford to skip work when heat symptoms persist. A doctor's visit costs him a full day's wages plus out-of-pocket fees—a burden he cannot absorb, since his employer does not provide health insurance. His situation reflects a wider regional crisis. Across Asia, populations are aging, healthcare needs are growing, and climate-related health risks are intensifying. Vulnerable populations—outdoor workers, older adults, people with chronic conditions—face escalating danger as temperatures rise.

This emerging reality is beginning to register with life and health insurers, who recognize that climate-related health risks now pose a structural threat to their business models and to the populations they serve. A forthcoming report from Forum for the Future, sponsored by AIA, examines how climate-related health risks are evolving across Asia and identifies opportunities for governments, healthcare providers, and insurers to build resilience. Amita Chaudhury, group head of sustainability at AIA, emphasized that heat is no longer a comfort issue but a health issue requiring urgent attention. "As climate-related risks evolve, there is a growing need to place greater emphasis on prevention, health engagement and helping people stay healthier for longer," she said. The report suggests that insurers can support climate-health resilience through better health awareness, preventive engagement, improved access to care, and collaboration with healthcare providers to strengthen system-wide capacity.

Yet significant gaps remain. While there is growing recognition that extreme heat affects health outcomes, far less is understood about how these impacts vary across different populations, geographies, and healthcare systems, or how prolonged heat exposure compounds chronic illness beyond acute heat stroke. The field of climate health in Asia remains evolving, fragmented, and underfunded. The challenge now is to move from recognition to action—to build data systems that capture heat's true mortality burden, to protect outdoor workers like Delos Santos through better workplace standards and accessible healthcare, and to strengthen health systems before the next record-breaking summer arrives.