As Europe endures another summer of record-breaking temperatures, a new study reveals that the health toll of extreme heat extends far beyond the well-known risks of heatstroke and dehydration. Researchers have identified 33 distinct conditions—ranging from skin eruptions to violent trauma—that surge during heatwaves, many of which are routinely overlooked in emergency care.
The study, published in Science Advances, analyzed nearly one million emergency department and urgent care visits in Chicago between May and September over a 12-year period. The authors found significant increases in diagnoses such as acute kidney failure, multiple sclerosis flare-ups, mental and behavioral disorders, and even insect bites and stings during periods of intense heat.
“It is a public health obligation to protect the individuals and communities most vulnerable to the harmful effects of climate change,” said lead author Hyojung Jang from Northwestern University. “If we’re only tracking the more commonly known heat-related illnesses, we’ll underestimate the true heat-related health burden, which could result in vulnerable people and communities being overlooked.”
Beyond the usual suspects
The study’s findings challenge the narrow focus on heat exhaustion and heatstroke that dominates public health messaging. Among the 33 conditions flagged were skin rashes and swelling, fluid and electrolyte imbalances, and renal complications that often manifest days after the initial heat exposure. The authors stress that emergency departments and urgent care centers should update their clinical alerts to include these broader diagnostic categories.
“Previous research has shown that when people are exposed to extreme heat, they often act more aggressively, so that may be playing a factor here,” said co-author Daniel Horton, also from Northwestern. “When it’s hot out, your body is stressed, and your mind is stressed, so that may be distracting or aggravating, and it could lead to more accidents.” Indeed, the study identified 23 specific injury, poisoning, or external-cause diagnoses—including assaults and firearm-related incidents—that met the criteria for being heat-related.
The implications for Europe are significant. From the extreme weather events battering the continent to the strain on healthcare systems in cities like Paris, Madrid, and Berlin, understanding the full spectrum of heat-related illness is critical. Urban environments face additional risks due to the “urban heat island effect,” which can raise local temperatures by several degrees and prolong heat events.
“The findings could help improve preparedness for future heat-intense periods,” the researchers note. This includes anticipating surges in demand for dehydration- and renal-related care during and immediately after heatwaves, as well as planning for the psychological and social impacts of extreme temperatures.
As Europe’s climate continues to warm, the study serves as a reminder that the health burden of extreme heat is far more complex than previously thought. For policymakers and public health officials across the EU, the message is clear: broaden the definition of heat-related illness, and invest in resilience measures that protect the most vulnerable.
