Europe is in the grip of yet another deadly heatwave. Over 10,000 excess deaths were recorded during late-June 2026 alone – and the toll keeps climbing.

With the acceleration of the climate crisis, heatstroke is predicted to become more prevalent. Understanding why it is so often fatal is now an urgent question.

Heatstroke happens when the body’s core temperature climbs above 40°C. This can cause the brain to malfunction, resulting in confusion and seizures. It can also cause muscles to break down and flood the bloodstream with damaging cellular waste.

All of this is dangerous on its own. But direct heat damage doesn’t fully explain why patients can die hours or days after their temperature has returned to normal. The answer lies in the immune system’s response.

Heatstroke tricks the body into launching the kind of all-out inflammatory attack it normally saves for life-threatening infections. Except there is no infection: the immune response is activated with no clear target, and it stays hyperactive long after the body........

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