As Heatwaves Intensify, Scientists Uncover the Hidden Toll of Rising Temperatures on the Human Brain
With climate change driving more frequent and extreme heatwaves, researchers are racing to understand how excessive heat disrupts brain function. One case that highlights this concern is Jake, who had his first tonic-clonic seizure at just five months old during a period of extreme heat. “He had overheated,” recalls his mother, Stephanie Smith, “and we witnessed what we thought would be the scariest thing we would ever see. Unfortunately, it wasn’t.”
Over the years, Jake’s seizures have been closely linked to high temperatures. Each summer, his family faces a relentless struggle to keep him cool and safe. At 18 months, Jake was diagnosed with Dravet Syndrome — a rare genetic neurological disorder affecting about 1 in 15,000 children. The condition is characterized by severe epilepsy, often coupled with intellectual disability, autism spectrum disorders, ADHD, and challenges with speech, motor function, and sleep. Heat and sudden temperature shifts are major seizure triggers.
#1Now 13, Jake continues to suffer from temperature-induced seizures.
"Rising summer temperatures and prolonged heatwaves are worsening the already devastating burden of this condition," says Smith.
Dravet Syndrome is just one of many neurological disorders exacerbated by heat, according to Dr. Sanjay Sisodiya of University College London, a neurologist and global leader in studying climate change’s impact on brain health. He began to observe a pattern as patients' families increasingly reported worsening symptoms during hot spells. "Of course the brain is affected — it's central to the body’s ability to regulate heat,” he explains.
Sisodiya’s research uncovered a long list of neurological conditions aggravated by heat and humidity, including epilepsy, stroke, encephalitis, multiple sclerosis, and migraines. He also discovered that these effects are not theoretical — they’re already showing up in population data. For example, during the 2003 European heatwave, around 7% of excess deaths were linked to direct neurological complications. Similar patterns were observed during the 2022 UK heatwave.
But heat doesn't just worsen medical conditions — it also changes how our brains behave. Studies show that extreme temperatures may lead to increased aggression, irritability, and even depression.
So, as global temperatures continue to rise, what future challenges will our brains face — and how can we prepare?
#2How Rising Heat Affects Brain Function: What Science Reveals
The human brain typically stays just about 1°C (1.8°F) warmer than the body’s core temperature. Yet, being one of the most energy-demanding organs, it generates significant heat during activities like thinking, remembering, and reacting. To keep brain temperature stable, the body relies on blood circulation, which dissipates this excess heat through an intricate network of blood vessels.
This cooling process is critical because brain cells are highly sensitive to temperature. Even slight changes can disrupt the function of neurotransmitters—the molecules responsible for sending messages between brain cells. When the brain overheats or cools down excessively, these processes may become inefficient.
“We don't yet fully understand how all these complex mechanisms interact,” says Dr. Sanjay Sisodiya, neurologist at University College London. “But you can think of it like a clock whose gears are no longer working in harmony.”
Extreme heat affects everyone’s brain to some degree, often impairing decision-making and increasing risk-taking behavior. However, individuals with neurological disorders are particularly vulnerable. Several factors contribute to this increased sensitivity. For instance, some conditions impair the body's ability to sweat—our natural cooling mechanism.
“Thermoregulation itself is controlled by the brain, and when certain regions are dysfunctional, it can be compromised,” explains Sisodiya. In diseases like multiple sclerosis, body temperature regulation can be significantly altered. Moreover, medications prescribed for neurological and psychiatric conditions—such as those for schizophrenia—can interfere with temperature control, making patients more susceptible to hyperthermia (dangerous overheating) and even heat-related fatalities
#3How Rising Temperatures Are Impacting Brain Health
As the planet heats up, the effects of extreme heat on the human brain are becoming increasingly concerning. Research shows that heatwaves, especially those with high nighttime temperatures, disrupt sleep quality, which in turn can negatively impact mood and intensify symptoms of certain neurological conditions. For instance, people with epilepsy may face a higher risk of seizures due to sleep deprivation caused by hot nights.
Heat and Vulnerable Populations
Elderly individuals and people with dementia are particularly at risk during heatwaves. Cognitive impairments can make it difficult for them to adapt to rising temperatures — they may forget to drink water, close windows, or stay indoors. This can lead to a rise in hospital admissions and mortality rates among this group.
Stroke Risk in a Warming World
Studies have also found a connection between heat exposure and stroke incidence. In an analysis of stroke mortality data from 25 countries, researchers discovered that the hottest days contributed two additional deaths per 1,000 cases of ischemic stroke. While that may seem minimal, it translates to more than 10,000 heat-related stroke deaths annually when scaled globally.
Unfortunately, low- and middle-income countries, which already face high stroke rates and severe climate impacts, bear the brunt of this burden. Rising global temperatures are expected to widen health inequalities across and within nations, especially among the elderly and those of low socioeconomic status.
Heat and Early Brain Development
Extreme heat isn’t just harming the elderly — it's also affecting the youngest. Exposure to high temperatures during pregnancy has been linked to premature births, increasing the risk of neurodevelopmental delays and cognitive impairments. A recent review found that heatwaves can increase preterm births by 26%, but more research is needed to understand which populations are most at risk and why some are more affected than others.
The Brain Under Heat Stress
Excessive heat can compromise the blood-brain barrier, allowing toxins, bacteria, and viruses to enter brain tissue more easily — a risk factor for neurodegenerative diseases. As temperatures rise, the spread of mosquito-borne viruses such as Zika, dengue, and chikungunya is also increasing. These viruses can cause severe neurological damage, especially in unborn children.
Genetic Susceptibility and Climate Change
Not everyone is affected by heat in the same way. Some people are genetically more vulnerable to the effects of heat due to specific genetic variants that influence protein structures or neurological responses. These thermo-latent phenotypes may only become apparent under the intense pressure of climate change, meaning today’s challenges for those with existing neurological disorders could be tomorrow’s problem for the wider population.
Conclusion: A Call for Awareness and Action
As global temperatures continue to rise, it is critical to understand how climate change affects brain health. From sleep disruption and increased seizure risk to stroke, dementia, and developmental issues, heat is influencing neurological health in complex and far-reaching ways. With more research, we can identify those most at risk and take proactive steps to protect vulnerable populations in an increasingly hot world.
#4Unanswered Questions and the Urgency to Act in the Era of Extreme Heat
Despite mounting research, critical questions remain: Is it the peak daytime heat, the duration of heatwaves, or persistently high nighttime temperatures that pose the greatest neurological threat? The answer may vary depending on individual physiology or the specific neurological condition.
Understanding who is most at risk—and why—is essential to creating effective mitigation strategies. These may include early warning systems, heat-resilience infrastructure, or financial safety nets such as insurance for day laborers who lose income due to extreme heat conditions.
As United Nations Secretary-General António Guterres declared in July 2023, "The era of global warming has ended; the era of global boiling has arrived." That month became the hottest ever recorded on Earth. Climate change is no longer a looming threat—it is a present and accelerating crisis. The “hot brain” era has begun, with serious implications for neurological health and global equity.
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