It’s in your head, but in a different way.

You’ve probably noticed it yourself. A stretch of sweltering days rolls in, and before long, you’re snapping at people, forgetting things, and staring at the wall instead of getting anything done. You chalk it up to being tired or uncomfortable. But scientists are now telling us something more worrying is going on. The heat isn’t just making you sweaty and miserable. It’s changing how your brain works.

This isn’t something a glass of lemonade is going to fix. Researchers across the world are scrambling to understand what happens inside our skulls when temperatures spike, and what they’re finding should get all of us paying attention, especially if you have children, or if you or someone you love has any kind of mental health condition.

Your Brain on Heat: What We Know So Far

For a long time, scientists knew that extreme heat killed people. Heart attacks, organ failure, heat stroke. The physical stuff was well documented. But the mental side of the equation got a lot less attention. That’s changing fast.

A large body of research now confirms what many of us have felt in our gut: when the mercury climbs, our moods and our minds go sideways. Studies show that people become more irritable and even more violent as temperatures rise. Cognitive psychologist Catherine Thompson at Liverpool Hope University has been studying this in firefighters, one of the few groups you can actually test in controlled heat conditions. After just 15 minutes of intense heat exposure, her subjects had a much harder time focusing and controlling their attention. It wasn’t permanent, but it was real.

The troubling part is that Thompson’s firefighters recovered after about 20 minutes of cooling down. But they had only been in intense heat for a short time. What happens to people who live through days of scorching temperatures with no relief? Nobody’s quite sure yet. It’s one of the hardest things to study because you’d need to ship testing kits to thousands of people with only a few days’ warning of a heat wave.

What’s Actually Happening Inside Your Brain

Animal studies have started to give us some answers about the biology. When rats and mice are exposed to high temperatures, levels of brain chemicals such as serotonin appear to rise. Serotonin is a chemical messenger that affects your mood, your sleep, and your ability to think clearly. When it gets thrown out of balance, things go wrong. Anxiety, depression, erratic behavior. Sound familiar on a bad heat day?

Beyond that, excessive heat appears to interfere with the way different networks in your brain talk to each other. Think of it like static on a radio signal. Everything works, technically, but the transmission is garbled. Heat may also affect how well oxygen gets to your brain cells. Add it all up and you have a biological mess that researchers are only beginning to map.

Dr. Joshua Wortzel, who runs the Heat-Mind Lab at Hartford HealthCare in Connecticut, puts it plainly: there are so many biological reasons why brains may be negatively affected by heat that the real challenge is figuring out which ones matter most and in what order.

If You Already Have a Mental Health Condition, Pay Attention

For people already living with a mental health condition, heat waves aren’t just uncomfortable. They can be genuinely dangerous. A major review from the University of Oxford found that hospital admissions for people with mental health conditions jumped nearly 10 percent during heat waves.

People with schizophrenia are particularly at risk. During the brutal 2021 heat dome that smothered much of Canada, people with schizophrenia were found to be three times more likely to die than the general population. Part of the reason is that many psychiatric medications affect the body’s ability to regulate temperature. Some suppress sweating. Others change blood flow. When temperatures soar, these drugs can turn a manageable situation into a fatal one.

And it’s not just the direct physical effects. Sleep is disrupted when it’s too hot. Exercise and outdoor socializing drop off. Both of those are critical for mental health. People get more isolated. The combination of all these factors during a heat wave creates a perfect storm.

Children Are in the Most Danger

If there’s one thing the newest research is making crystal clear, it’s this: children bear a disproportionate burden when heat hits. And the damage may not show up for years.

Researchers at the Barcelona Institute for Global Health scanned the brains of over 2,600 children using MRI technology and found that babies and toddlers exposed to heat had measurable changes in the white matter of their brains by the time they reached ages nine to twelve. White matter is essentially the brain’s wiring. It connects different regions and allows them to communicate. When it doesn’t develop properly, thinking, learning, and emotional regulation can all be affected. Children from poorer neighborhoods showed the greatest vulnerability, likely because they have less access to air conditioning and green spaces that help buffer extreme heat.

A separate large study drawing on data from over 100,000 children across hundreds of Chinese cities found that extreme heat during pregnancy and during a child’s first three years of life was linked to a significantly higher risk of suspected developmental delays. The risk from postnatal heat exposure was more than 50 percent higher compared to moderate temperatures.

The connection to suicide in young people is also alarming. Dr. Wortzel and colleagues found nearly a three percent increase in the suicide rate among Americans aged 15 to 24 for every single degree Celsius increase in average monthly temperature. That’s more than double the rate seen in adults over 24, which is already concerning enough.

A 2025 study from North Carolina found that young people with ADHD who experienced heat waves had a 17 percent higher risk of emergency room visits for major depression, and a 30 percent higher risk for combined depression and suicidal behavior. Teenagers aged 12 to 17 showed the steepest increases.

Why This Is About to Get Much Worse

Heat waves aren’t a freak occurrence anymore. In the United States, the frequency of heat waves has risen from about two per year in the 1960s to six per year in recent years, and they’re lasting longer and running hotter. Children born in 2020 are projected to experience roughly seven times the number of heat waves their grandparents did. That’s not a distant future scenario. Those children are in elementary school right now.

Researchers are calling for public health strategies that treat heat as the mental health emergency it is, not just a physical one. That means cooling centers for people with psychiatric conditions. It means rethinking how we prescribe medications that affect heat regulation. It means checking in on neighbors. It means treating a heat wave alert with the same seriousness we give a blizzard warning.

What You Can Actually Do

If you or a family member takes psychiatric medication, talk to your physician before the next heat wave hits. Ask directly whether your medication affects sweating or body temperature regulation. The answer may surprise you.

For children, keep them indoors during peak heat hours, make sure they’re drinking water consistently, and watch for signs of unusual irritability, withdrawal, or mood changes that go beyond simple crankiness. These can be early signals that the heat is affecting more than their comfort.

Sleep matters more than ever in a heat wave. A room that’s even a few degrees cooler can make a significant difference in sleep quality, and poor sleep amplifies every mental health challenge there is.

Check in on elderly neighbors and relatives. Check on people you know who have schizophrenia, bipolar disorder, or depression. They may not recognize that the heat is making things worse, and they may be less able to take action on their own. In fact, some psychotropic medications can inhibit a person’s ability to appropriately monitor their body’s heat. I knew of one case where a young man, playing basketball at an indoor court where the temperature was 95 degrees, dropped dead. He never realized how high his internal body heat was rising until it killed him.

The science here is still developing. Researchers don’t have all the answers yet. But one thing is already clear: the heat is not just a problem for your body. Your brain is in there too, working hard to keep everything running, and it needs you to take this seriously.