This summer, Europe has faced some of its most extreme temperatures, with thermometers reaching record high temperatures over several consecutive heatwaves. The scorching weather has caused thousands of excess deaths, strained healthcare facilities and highlighted the need for better preparedness going forward. Extreme temperatures can have dangerous health consequences, with heat exhaustion, heatstroke and dehydration being among the most common. However, researchers have identified more than 30 diagnoses associated with high temperatures, ones that show a significant increase during periods of intense heat.The research, published in the journal Science Advances, found strong links to under-recognised problems such as multiple sclerosis flare-ups, skin eruptions and various physical injuries.“It is a public health obligation to protect the individuals and communities most vulnerable to the harmful effects of climate change,” said the study’s author Hyojung Jang, from Northwestern University in the United States. “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.” This study examined 1,803 diagnoses recorded across almost one million emergency department and urgent care visits in Chicago between May and September between 2011 and 2023. 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. The authors noted that urban environments face additional risks because of the so-called “ urban heat island effect,” which can raise local temperatures by several degrees and extend the length of such events. The findings also suggest that extreme heat may be linked to a rise in accidental and violent trauma, including assaults and firearm-related incidents. The researchers identified 23 specific injury, poisoning or external-cause diagnoses that met their criteria for being heat-related.“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 preparednessAccording to the researchers, the findings could help improve preparedness for future heat-intense periods. This includes updating clinical alerts for a broader range of conditions, specifically renal and fluid-balance complications, which often manifest several days after the actual heat exposure.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 noted the findings are currently limited to the Chicago study and should be replicated in other populations, climates and health care systems.