There’s a Scientific Reason Why You Feel Grumpier When It’s Insanely Hot Outside—And Also Something You Can Do About It

There’s a common phrase about summertime weather where I live in the Mid-Atlantic: “It’s not the heat that gets you. It’s the humidity.” Whatever it is, when the temperature climbs into the high 80s and beyond, it’s pretty miserable. Being outdoors for mere minutes can leave you dripping with sweat, and wearing even the thinnest of clothing can feel like you’ve donned a wool sweater. And sleeping soundly? Forget about it.

Even the most calm, cheerful and mild-mannered among us might notice their mood worsens on extremely hot days. And they’re right: The heat can make us feel cranky, irritable or downright angry—and there’s a scientific reason for it.

I talked to Brynna Connor, MD, a family medicine physician and health-care ambassador at Northwest Pharmacy, and Rachel Marquez, MD, a family medicine doctor and regional medical director of external affairs at Kaiser Permanente Mid-Atlantic, to find out why the heat affects our mood. I also dug into the latest research about this sweltering phenomenon, so keep reading to learn what you can do to stay cool out there.

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How bad can things get when it’s ridiculously hot out?

Pretty bad, which is especially concerning now, given that we’re experiencing more heat stress days more often—up to 50 more days per year in some places, according to the latest research. Nights are getting hotter and staying hotter too.

A 2026 study published in the Nature Portfolio journal Communications Sustainability found a link between even short-term spikes in temperature and greater incidence of violence, both interpersonal and self-inflicted. Researchers found that as the temperature rose, the number of violence-related hospital visits increased, particularly in the first two days of high heat. Another study discovered that when temperatures exceeded a mild 70 degrees, there were more violent crimes in Los Angeles.

In 2023, researchers in South Korea came to the same conclusion: The risk of deaths by assault increased as temperatures rose, especially among males, teenagers and those with less education. In prisons, which often lack adequate air-conditioning and ventilation, the probability of violence rose when temperatures climbed above 80 degrees.

This phenomenon is called the temperature-aggression or heat-aggression hypothesis, and it can even affect our interpretations of conversations and people’s tone. And researchers have been keying in on this for decades: A 2000 study found that when we’re uncomfortably hot, we perceive other people and other interactions as being more hostile.

What happens to your body in extreme heat?

Extreme heat triggers the body’s stress response as it fights to keep cool. Part of that response is the release of the stress hormones cortisol and adrenaline, which “increase the feeling of restlessness and being on edge,” says Dr. Marquez.

The body has a limited amount of energy available to it at any given time, explains Dr. Connor. On extremely hot days, the body expends a lot of that energy keeping our core body temperature at normal levels (between 97 and 99 degrees). “This leaves less energy available for things like concentration and emotional regulation,” she says.

In order to keep the body cool, Dr. Connor says, the “blood vessels in the skin enlarge to release heat, your heart pumps more rapidly to bring the blood to the skin, and you sweat more to cool yourself through evaporation.”

Hot days can also stress out our brains, which must also stay within an optimal temperature range to function properly. “When body temperature rises, your attention span decreases, reaction time slows and decision-making becomes more difficult,” Dr. Connor says.

Why does this make us so grumpy—or even outright angry?

The body perceives extreme heat as more than just discomfort. “The reason we get more irritable and grumpy when the weather is really hot is that our bodies are experiencing real physiological stress, which changes how both the brain and body function,” Dr. Connor says. The brain’s prefrontal cortex, which is responsible for impulse control, judgment and emotional regulation, doesn’t work as efficiently and effectively in extreme heat. But the emotional centers of our brains do stay active. This combination can translate to anger and impulsivity.

“Little triggers can feel larger or more significant, since the body is already under stress,” Dr. Connor says. “Heat can lower the threshold for aggressive or irritable responses as it becomes more difficult for the brain to regulate emotions.”

Because we’re sweating more to cool down, it’s easier to become dehydrated. “Sweating causes you to lose both water and electrolytes, such as sodium and potassium,” Dr. Connor says. “Even mild dehydration can result in symptoms like headache, fatigue, difficulty concentrating, irritability and slower cognitive processing.”

Heat also makes sleeping practically impossible—and we all know we’re not our best selves after a night of bad sleep. “Sleep is one of the best tools we have for keeping our emotions balanced,” Dr. Marquez says. Our core body temperature has to drop to fall and stay asleep, and that is really tricky in sweltering heat.

Does grumpiness or anger in extreme heat signal a more serious health issue?

Irritability is a normal response to the heat, Dr. Marquez says, but it’s also one of the recognized symptoms of heat exhaustion, along with headache, nausea, dizziness and cold, clammy skin.

“Watch for the change from irritable to confused or agitated, since that can mean that heat exhaustion could be progressing toward heatstroke, which is a medical emergency,” Dr. Marquez says. “If you or someone with you is experiencing confusion, a seizure, hot, dry skin or loss of consciousness, call 911 right away. Grumpy is normal. Confused is not.”

High temperatures can pose serious—and potentially deadly—health risks. “Extreme heat is a community-wide health concern,” Dr. Marquez says. “Check in on the people around you, especially those who live alone. Older adults, young children and people managing chronic health conditions can be particularly vulnerable to heat-related illness.”

How can we keep our cool in the heat?

If the heat is starting to make your blood boil, here are some tips for managing your mood and cooling off.

Stay hydrated

If you’re feeling grumpy, foggy or generally out of sorts, drink a glass of water (or two). More heat means more sweating, which means faster dehydration. Even slight dehydration can cause headaches and irritability.

“Drink water throughout the day instead of waiting until you’re thirsty,” Dr. Connor says. “If you’ve been sweating heavily for several hours, you may also need drinks with electrolytes to replace what’s been lost.”

Shift your outdoor routines

Physical activity and spending time outdoors are normally two of the best ways to relieve stress and boost your mood, but doing those things when it’s really hot isn’t the best idea. Tweak your routine a bit.

“If your routine typically includes outdoor exercise, yard work or other time outside, consider moving those activities indoors, rescheduling them for cooler parts of the day or taking more frequent breaks from the heat,” Dr. Marquez says.

Try running on the treadmill at the gym instead of outside. Move your usual post-lunch walk to early morning or evening to avoid the midday sun. Even light stretching or yoga can help you feel better.

Socialize with others

When it’s really hot, we might want to hunker down inside with the AC. But getting out and spending time with friends or family can improve your mood. Catch up with a friend over an iced coffee or chilled cocktail (though don’t overdo it, as coffee and alcohol can increase dehydration). Take it from kids: Water can cheer most anyone up, so gather some people to hang out at a local pool, lake or stream.

Make sure you’re eating enough

We often don’t feel like eating much when it’s extremely hot, but a grumbling stomach can quickly turn into “hanger.” Plus, the body is working overtime to regulate our body temperatures and needs those calories for fuel.

Dr. Connor recommends keeping meals light. “Eating cold foods, fruits, vegetables, yogurt or salads can help you feel more comfortable on hot days,” she says. “Large or heavy meals can increase heat production due to digestion.”

Dress smart

Some colors and fabrics can trap heat and moisture, making us feel even hotter and more uncomfortable. Skip heavy denim, dark colors, form-fitting outfits and synthetic fabrics. Even your jewelry might need an overhaul. Gold and silver jewelry are conductors and will trap heat close to the body.

“Wear lightweight, loose-fitting fabrics, ideally in light colors, in breathable materials such as cotton, linen or other moisture-wicking fabrics,” Dr. Connor says.

How can you lower your body temperature quickly if there’s no AC in sight?

Even if you live or work somewhere without air-conditioning, there are still steps you can take to cool down. Here’s what the experts suggest:

• Keep window blinds, shades or curtains closed during the hottest hours of the day, typically between 3 and 6 p.m. Open them back up at night, when the temperature cools down.
• Apply a cool, damp towel or splash cold water on parts of the body where large blood vessels are close to the skin: neck, wrists, forearms and behind the knees. Immersing your hands in cold water for a few minutes will also bring your temperature down.
• Take a cool shower, drench your shirt in water or mist yourself with a cooling spray or cold water.
• Try to find some AC. If you can get access to any air-conditioning, like a single window unit in a bedroom or at a public place like a library, sit in that space long enough for your core temperature to come down, not just your skin, Dr. Connor says. “Typically this occurs within 30 to 60 minutes, but in instances of heat stress or heat exhaustion, it could take up to 24 to 48 hours, plus fluid replenishment,” she says.

Sources:

• Brynna Connor, MD, family medicine physician and health-care ambassador at Northwest Pharmacy; email interview, July 21, 2026
• Rachel Marquez, MD, family medicine doctor and regional medical director of External Affairs at Kaiser Permanente Mid-Atlantic; email interview, July 22, 2026
• Guardian: “Why does hot weather put me in such a bad mood?”
• Nature Climate Change: “Global heat stress intensification and its expanding footprint on the human population”
• Community Sustainability: “Higher temperatures are associated with increased interpersonal and self-inflicted violence-related Medicaid hospital visits in the United States”
• ScienceNews: “How extreme heat from climate change distorts human behavior”
• Yale Journal of Biology and Medicine: “Positive Association of Aggression with Ambient Temperature”
• Advances in Experimental Social Psychology: “Temperature and aggression”
• Anxiety and Depression Association of America: “Physical Activity: An Evidence-Based Way to Reduce Stress”
• American Heart Association: “Spending Time in Nature to Reduce Stress and Anxiety”

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