Extreme heat does more than cause heatstroke and dehydration. A study published in Science Advances and reported by Euronews Business shows that, during the summer months of May through September from 2011 to 2023, Chicago’s emergency‑department and urgent‑care facilities recorded statistically significant increases in 33 separate diagnoses on extreme‑temperature days.
How the study was built
The researchers assembled a data set of almost 1,000,000 visits to Chicago emergency departments and urgent‑care centres over the 12‑year summer period. Within that pool they examined 1,803 distinct diagnostic codes, covering everything from common infections to rare neurological events. The full scope of the data set – “almost one million emergency‑department and urgent‑care visits in Chicago” – is documented by Euronews Business, which cites the original Science Advances paper.
By matching daily temperature records to the dates of each visit, the team identified which diagnoses rose on days classified as “extreme‑heat”. The statistical threshold required a diagnosis to show a clear, repeatable uptick on those hot days compared with typical summer days.
Key findings: more than 30 diagnoses rise with heat
Across the 33 heat‑related diagnoses, the study highlights several groups that have previously been ignored in public‑health monitoring:
- Kidney problems – acute kidney failure showed a measurable increase on hot days.
- Neurological flare‑ups – multiple sclerosis episodes were more common when temperatures spiked.
- Skin reactions – rashes and swelling rose significantly, as did insect bites and stings.
- Mental and behavioural disorders – the data captured a rise in presentations for anxiety, depression and other behavioural conditions.
- Injuries – 23 specific injury, poisoning or external‑cause diagnoses met the study’s heat‑related criteria, indicating more accidental and violent trauma during heat spikes.
“The researchers identified diagnoses such as skin rashes and swelling, acute kidney failure, multiple sclerosis, mental and behavioural disorders and insect bites and stings, which were associated with heat and are often overlooked in emergency settings,” Euronews Business reported.
Overall, the study found “more than 30 diagnoses associated with high temperatures, ones that show a significant increase during periods” of extreme heat, confirming the central claim that the health impact of heat extends far beyond the classic heatstroke and dehydration metrics.
Why the findings matter for health systems
European cities are currently grappling with record‑breaking heatwaves, and policymakers are looking for evidence‑based ways to protect hospitals and clinics. The Chicago analysis provides a concrete benchmark: if a city experiences a similar number of extreme‑heat days, health services should anticipate not only classic heat illnesses but also a surge in kidney emergencies, neurological flare‑ups, skin conditions and injury‑related visits.
Public‑health planners can use the 33‑diagnosis list to broaden heat‑alert protocols. For example, emergency‑department triage tools could flag patients presenting with acute kidney injury or multiple‑sclerosis symptoms on hot days for closer monitoring. Likewise, mental‑health services might prepare for higher demand during heat spikes, a point underscored by the study’s identification of mental and behavioural disorders as heat‑sensitive.
Injury‑related spikes are especially noteworthy. The 23 injury diagnoses include assaults, firearm injuries and other violent trauma, suggesting that extreme heat may exacerbate aggression or risky behaviour. While the packet notes that “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,” the Chicago data give the first large‑scale empirical backing for that hypothesis.
Table: Heat‑related diagnoses identified in the Chicago emergency‑department study (2011‑2023)
| Diagnosis Category | Heat‑related? (Yes/No) |
|---|---|
| Acute kidney failure | Yes |
| Multiple sclerosis flare‑up | Yes |
| Skin rashes / swelling | Yes |
| Mental & behavioural disorders | Yes |
| Insect bites & stings | Yes |
| Assault / firearm injuries | Yes |
| Other injuries (23 total) | Yes |
| Source: Euronews Business – Science Advances study | |
Context and timeline
The data collection spanned every summer month (May‑September) from 2011 through 2023, giving a 12‑year window that captures a range of temperature extremes. The Euronews Business article summarising the study was published on 27 August 2026, bringing the findings to a broader audience just as Europe confronts a new wave of heat events.
Because the study looks at a long historical period, it can serve as a baseline for future monitoring. Health authorities can compare the frequency of extreme‑heat days in upcoming summers with the 2011‑2023 record to gauge whether the burden on emergency services is likely to grow.
What remains unknown
The packet notes that the original Science Advances paper is the primary source, but the Euronews summary does not provide detailed effect sizes for each diagnosis. Consequently, the exact magnitude of increase—for example, whether acute kidney failure visits double on a 40 °C day or rise by a smaller percentage—cannot be stated without further data.
Moreover, the study focuses on Chicago, a large U.S. city with a specific climate, healthcare infrastructure and demographic profile. Whether the same 33 diagnoses will show similar heat‑sensitivity in European or Canadian cities remains an open question that local researchers will need to explore.
Looking ahead
For policymakers, the takeaway is clear: heat‑related health alerts should be broadened beyond the classic triad of heatstroke, dehydration and electrolyte imbalance. By incorporating the 33 diagnoses highlighted by the Chicago analysis, emergency departments can better allocate resources, clinicians can anticipate atypical presentations, and public‑health campaigns can warn vulnerable populations about a wider set of risks.
As Europe endures increasingly severe heatwaves, the Chicago evidence offers a data‑driven roadmap for expanding clinical alerts and preparing health systems for the full spectrum of heat‑induced morbidity.