As global temperatures climb, scientists warn that extreme heat is no longer just a threat to the planet. It is increasingly shaping how our brains function, how we think, remember, feel, and, for many, how they survive.
As heat waves grow more intense and frequent under the pressure of climate change, researchers around the world are turning their attention to a question that was once rarely asked: what does extreme heat do to the human brain?
For Stephanie Smith, this question became painfully real when her son Jake was just five months old. On a sweltering summer day, Jake’s body suddenly stiffened before jerking uncontrollably in a tonic clonic seizure. “It was unbearably hot,” Smith recalls. “We thought we were witnessing the most terrifying moment of our lives. Sadly, it was only the beginning.”
As the years passed, the pattern became clear. Hot, humid days brought more seizures. Summer became a season of anxiety rather than freedom. The family turned to every cooling strategy they could manage, knowing that rising temperatures could mean medical emergencies.
At 18 months, Jake was diagnosed with Dravet syndrome, a rare neurological disorder affecting roughly one in 15,000 children. The condition includes severe epilepsy and is often accompanied by intellectual disabilities, autism, ADHD, speech and movement difficulties, and disrupted sleep. For children like Jake, heat is not just uncomfortable. It is dangerous.
Now 13 years old, Jake continues to experience seizures triggered by temperature shifts. “The hotter summers and longer heat waves are adding a heavy burden to an already devastating condition,” Smith says.
Jake’s story is deeply personal, but it reflects a much wider and growing public health concern.
Neurological conditions under thermal stress
Dravet syndrome is just one of many neurological disorders worsened by rising temperatures. According to Professor Sanjay Sisodia of University College London, a neurologist and leading researcher in climate change and brain health, heat acts as an amplifier for existing neurological vulnerability.
Sisodia, who specializes in epilepsy, says he regularly hears from families reporting that symptoms worsen during extreme heat. “That made me ask a simple question,” he explains. “Why wouldn’t climate change affect the brain? After all, many of the brain’s core processes are tied to how the body handles heat.”
When Sisodia reviewed global research, the evidence was striking. Elevated temperature and humidity were linked to worsening outcomes in epilepsy, stroke, encephalitis, multiple sclerosis, migraines, Parkinson’s disease, and several neurodegenerative and psychiatric conditions.
Historical data offers sobering confirmation. During the 2003 European heatwave, roughly seven percent of excess deaths were directly linked to neurological causes. Similar patterns emerged during the United Kingdom’s 2022 heatwave.
Heat also affects mental health more broadly. Research shows it increases irritability, aggression, anxiety, depression, and emotional instability. Decision making becomes impaired. Risk taking rises. Cognitive clarity declines.
Why heat disrupts the brain
The human brain is uniquely vulnerable to temperature changes. Under normal conditions, it operates within a narrow thermal range, rarely rising more than one degree Celsius above core body temperature. Yet the brain consumes more energy than any other organ, generating significant internal heat as it thinks, remembers, and responds.
To keep brain temperature stable, the body relies on blood circulation to carry excess heat away. When environmental temperatures rise, this cooling system is pushed to its limits.
Brain cells are exceptionally sensitive to thermal stress. Even slight deviations can disrupt the molecules that transmit signals between neurons. “Think of it like a finely tuned clock,” Sisodia explains. “When temperature interferes, the gears stop working in harmony.”
Excessive heat can impair attention, memory, reaction time, and judgment even in healthy individuals. For those with neurological conditions, the effects are far more severe.
In some disorders, sweating and thermoregulation are already compromised. Certain regions of the brain that regulate body temperature may not function properly. In multiple sclerosis, for example, even small increases in body temperature can worsen symptoms dramatically.
Medications also play a role. Drugs used to treat epilepsy, schizophrenia, depression, and other neurological or psychiatric conditions can interfere with temperature regulation, increasing the risk of hyperthermia and heat related death.
Sleep disruption and seizure risk
Heat waves, particularly high nighttime temperatures, disrupt sleep patterns. Poor sleep affects mood, concentration, and emotional regulation. For people with epilepsy, sleep deprivation significantly increases seizure risk.
“For many epilepsy patients, sleep is protective,” Sisodia notes. “When heat robs them of rest, the brain becomes more unstable.”
This creates a dangerous cycle: heat disrupts sleep, poor sleep worsens neurological symptoms, and those symptoms further impair the body’s ability to cope with heat.
Dementia, heat, and hidden danger
Older adults with dementia face heightened risks during extreme heat. Studies show increased hospitalization and mortality among dementia patients during heat waves.
Several factors contribute. Aging bodies regulate temperature less efficiently. Cognitive impairment makes it harder to recognize danger, stay hydrated, or respond appropriately to rising temperatures. Patients may forget to drink water, close windows, or avoid going outside in intense heat.
As global temperatures rise, dementia related heat mortality is expected to increase, particularly in regions with limited access to cooling infrastructure.
Heat and stroke risk
Rising temperatures are also linked to higher rates of stroke and stroke related deaths. A large study analyzing stroke mortality across 25 countries found that for every 1,000 ischemic stroke deaths, hot days contributed to two additional fatalities.
“That may sound small,” says Dr Bethan Davies of Sussex University Hospital. “But when you consider that around seven million people die from stroke worldwide each year, heat could be responsible for more than 10,000 additional deaths annually.”
The burden is expected to fall disproportionately on middle and low income countries, which already experience higher stroke rates and are more exposed to climate extremes.
“Rising temperatures will deepen health inequalities,” Davies warns. “Both between countries and within societies.”
Heat and the developing brain
Climate change is not only affecting aging brains. It is also influencing early neurodevelopment.
Extreme heat has been linked to adverse pregnancy outcomes, including preterm birth. According to Professor Jane Hirst of Imperial College London, a systematic review of studies found that heat waves are associated with a 26 percent increase in premature births.
Premature birth significantly raises the risk of neurodevelopmental delays, learning difficulties, and long term cognitive impairment.
“There is still much we don’t understand,” Hirst says. “Millions of women give birth each year in hot climates without complications. So we need to identify who is most at risk and why.”
A weakened brain under climate pressure
Extreme heat places additional stress on the brain, increasing vulnerability to injury and long term damage. It can weaken the blood brain barrier, the protective shield that prevents toxins, bacteria, and viruses from entering brain tissue.
As temperatures rise, infectious risks also grow. Warmer climates extend mosquito breeding seasons, increasing the spread of viruses such as Zika, Dengue, and Chikungunya. Many of these infections have serious neurological consequences.
“The Zika virus directly affects fetal brain development,” explains Tobias Sutter of the Swiss Institute of Tropical and Public Health. “As temperatures rise, mosquito activity starts earlier and lasts longer.”
Heat also alters how nerve cells communicate, affects the stability of neurological medications, increases suicide risk, and intensifies climate related anxiety and distress.
Why some brains suffer more than others
One of the most pressing questions facing scientists is why people respond differently to heat. Some tolerate extreme temperatures relatively well. Others deteriorate rapidly.
Genetics may play a role. Certain genetic variants affect protein structure, potentially making some individuals more sensitive to heat induced neurological stress.
“Some vulnerabilities only become visible when environmental pressure crosses a certain threshold,” Sisodia explains. “What we see today in people with neurological disorders may extend to the wider population as climate change accelerates.”
Preparing for a hotter cognitive future
Many questions remain unanswered. Researchers are still determining whether peak temperatures, duration of heat waves, or elevated nighttime heat causes the greatest neurological harm. The effects likely vary between individuals and conditions.
Protecting vulnerable populations will require targeted strategies. Early warning systems, heat adaptive urban design, access to cooling, medical guidance during heat events, and financial protections for workers exposed to extreme heat will all be critical.
As United Nations Secretary General António Guterres warned after July 2023 became the hottest month on record, “The era of global warming is over. The era of global boiling has arrived.”
Climate change is no longer a distant environmental issue. It is reshaping human health in real time. The age of hot brains has already begun.
