Double exposure portrait of young fitness Woman hand wiping sweat and summer heat wave concept; city skyscrapers in background

Extreme Heat is Bad for Your Health

We love a sunny, hot day but too much heat can cause many health problems. Some are mild, like swelling in the hands or feet. Others are more dangerous, like confusion, seizures, or passing out. Heat is the greatest weather-related killer in the United States.   

Emergency medicine physician Christopher Tedeschi

Christopher Tedeschi

High temperatures are not a promise you’ll get sick, but the more you’re exposed to hot environments, the higher your risk. So we asked an emergency medicine doctor how to beat the summer heat. And why.  

“Extreme heat can affect virtually all our body systems and can progress to life-threatening illnesses like heat stroke,” says Christopher Tedeschi, MD. People of all ages are susceptible. Heat illness happens when your body cannot cool down.

Heat illness isn’t simply about being uncomfortable. When the weather is hot, doctors and nurses in the emergency department see everything from heat rash to loss of consciousness. Tedeschi is director of emergency preparedness for the Department of Emergency Medicine at Columbia UniversityVagelos College of Physicians and Surgeons. Summer in New York City is prime time for heat illness emergencies.  

“Elevated temperatures stress our cardiovascular systems, cause damage to kidneys and liver, and can lead to confusion, delirium, and seizures,” says Tedeschi. Damage can be permanent or lead to greater, life-threatening medical complications. 

The best way to reduce body heat and avoid heat illness is to pay attention to your body and cool off when you’re feeling hot. 

Who gets heat illness? 

Anyone exposed to extreme heat can get a heat illness. Some are more susceptible than others: people who are sick or immunocompromised, taking certain medications, working outdoors, over age 60, and athletes of all ages.  

“As we get older our bodies have a more difficult time regulating temperature, and we see several cases of heat stroke in older patients each summer,” says Tedeschi. Also seen: young children left in parked cars. 

Certain medications (anticholinergics) reduce the body’s ability to dissipate heat. These include antihistamines, some antidepressants, and diuretics (often taken for high blood pressure or cardiac problems). 

Symptoms of heat exhaustion, heat illness, and heat stroke  

Your body temperature does not need to rise to experience heat illness. Common signs of heat illness:  

  • Dizziness 
  • Nausea and vomiting 
  • Headache 
  • Lethargy 

Heat illness can be hard to identify because the symptoms can be caused by other medical conditions, and people with heat illness often have normal body temperatures (97° - 99°F). To differentiate, think about the world around you. If it’s a hot day indoors or out, and you or anyone around you has any of these symptoms, stop whatever you’re doing immediately. Then rest, hydrate, and get to a cool place. Why? Heat exhaustion can lead to collapse, a complete breakdown of your body known as heat stroke.  

Heat exhaustion versus heat stroke  

Heat exhaustion describes abnormal symptoms experienced after exposure to high heat or strenuous exercise. Body temperature can be normal (97° - 99°F) or slightly elevated. Heat exhaustion can progress to heat stroke.  

Heat stroke is when body temperature is over 104°F and your body is out of whack: loss of consciousness, seizure, altered mental status, or other nervous system abnormality. Heat stroke can follow heat exhaustion or happen on its own.  

Heat and hydration 

Heat can cause some degree of dehydration by causing us to sweat more and our blood vessels to dilate, but you don’t need to be dehydrated to be ill from heat. If your body generates more heat than it can shed, no matter how hydrated you are, you can experience heat illness, especially heat stroke.  

How to reduce body heat in summer 

Our bodies naturally offload heat by sweating. But sweat needs to go somewhere. In dry weather, sweat is absorbed by the air through evaporation. In wet and humid weather, it’s harder for the air to absorb sweat. Think of how much hotter you are on a humid day.  

The best way to stay cool in hot and humid weather: 

  • Avoid excess heat exposure 
  • Take frequent breaks from strenuous activity 
  • Plan activities for cooler times of day 
  • Stay well hydrated  
  • Wear light, loose-fitting clothes 
  • Wear head coverings, like hats with brims  
  • Rest and hydrate frequently, especially important for kids 

“If it’s super hot, I like to dip a bandana in cold water and tie it around my neck,” says Tedeschi.  

When summer heat waves strike (or if you’re traveling from a cooler location to a hot one), take it slow, gradually increasing your exposure to heat and activity. You can become "heat acclimated" by gradually increasing exposure to heat and activity in hot weather.

The most important thing to know about heat illness is it’s preventable. Use common sense to avoid excess heat exposure. Do what you can to stay cool so you can stay out of the emergency room.    


Christopher Tedeschi, MD, is associate professor of emergency medicine at Columbia University Vagelos College of Physicians and Surgeons and director of emergency preparedness for the Department of Emergency Medicine at Columbia University Irving Medical Center.