Beyond Heatstroke: Study Links Extreme Heat to 33 Unexpected Health Conditions

Europe this summer has faced some of its most extreme temperatures, with record highs during several consecutive heatwaves. The scorching weather has caused thousands of excess deaths, strained healthcare facilities and highlighted the need for better preparedness.

Extreme temperatures are known to cause illnesses such as heat exhaustion, heatstroke and dehydration. However, researchers have identified more than 30 additional diagnoses that become significantly more common during intense heat, many of which are under‑recognised in emergency settings.

The study, published in Science Advances, analysed 1 803 diagnoses recorded across nearly one million emergency‑department and urgent‑care visits in Chicago between May and September from 2011 to 2023. It found strong links between high temperatures and conditions ranging from skin rashes and swelling to acute kidney failure, multiple‑sclerosis flare‑ups, mental‑behavioural disorders, insect bites and stings, and even injuries related to violence or accidents.

“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 of 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.”

Urban environments add another layer of risk because of the “urban heat‑island effect,” which can raise local temperatures by several degrees and extend the duration of heat events. The researchers also noted that extreme heat may increase aggression and accidental trauma, identifying 23 specific injury, poisoning or external‑cause diagnoses that met their criteria for heat‑related outcomes.

“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, associate professor at 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.”

Improving preparedness

The findings could help improve preparedness for future heat‑intense periods. This includes updating clinical alerts for a broader range of conditions, especially renal and fluid‑balance complications that often manifest several days after heat exposure.

By considering these possible diagnoses, emergency departments and urgent‑care settings can better anticipate and prepare for surges in demand for dehydration‑ and renal‑related care during and immediately after extreme heat events.

The authors caution that the results are currently limited to the Chicago study and should be replicated in other populations, climates and health‑care systems before broader applications can be made.

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