Heat waves are more dangerous than you think. Here’s why, and how to stay safe

Editor's note: A version of this article was originally published in July 2023. It has been updated with data on the ongiong heat wave and additional questions. 

The numbers are staggering:

In what the National Weather Service has described as a “never-ending heat wave,” records continued to fall across the West this week: 120 degrees Farenheit (49 degrees Celsius) in Las Vegas; a low that never dipped below 92 F in Phoenix; Five straight 100-plus F days in Oregon.  In Death Valley it was so hot (128 F) that helicopters couldn’t fly to the rescue when the heat sickened motorcyclists. One died and another was hospitalized.

“More people die of heat than any other weather-related event, but it is just not publicized in the same way. We don’t name heat waves like we do with hurricanes, and when you look outside there’s nothing to really see so people tend not to consider heat dangerous,” says Colleen Reid, an assistant professor of geography at CU Boulder who studies the health impacts of extreme heat. “But it is.”

With forecasters predicting triple-digit temperatures for three days this weekend on Colorado’s Front Range, and climate change predicted to lead to hotter, longer and more frequent heat waves in the future, CU Boulder Today got Reid’s take on their health impacts, who is the most vulnerable, and what people can do.

What goes on inside your body when exposed to extreme heat? 

Your body tries to cool off as best as it can, so you sweat more. When you sweat, you lose electrolytes, and you need those electrolytes for lots of different bodily functions. You are also losing fluid, so you can get dehydrated, which can cause confusion and inhibit the good judgment it takes to stop and cool off. Sometimes people don’t know the heat is impacting them until it’s too late. Or, if they are out hiking or running, they get lost. If you can’t cool off, your insides essentially cook.

We know from research that people are more likely to have heatstroke and show up in the hospital or the emergency department with electrolyte imbalance or kidney problems during a heat wave. About 1,200 people die n the U.S. each year from heat-related illness. (By comparison, about 88 perish in floods and 68 from tornadoes.)

It’s staying hot for days. Is this more dangerous?

The longer the duration of a heat wave, the worse the health outcomes are. If the temperature goes up for a short period of time, we have physiological and behavioral responses that can help us cope. But when it lasts longer it can overwhelm the body’s ability to handle it. Additionally, people are willing to take precautionary measures for a while but after a while they want to get on with things and just go out in the heat anyway.

Are certain populations particularly vulnerable?

People with kidney disease, as kidneys are very affected by the heat. Some prescription medications (including psychotropics, diuretics and medications for Parkinson’s disease) also interfere with body temperature regulation. The elderly, as their bodies have trouble thermoregulating just due to the natural aging process. Similarly, really young children, particularly those too young to be able to use words to explain their discomfort. And, of course, anyone who does not have access to places to cool off. 

Are there socioeconomic factors at play here, too?

Yes. We know from my research and that of others that homes that have air conditioning are more likely to be homes owned by wealthier families. And even when people have an air conditioner but are struggling to pay their electric bill, they don't always turn it on. People with lower economic means also tend to live in communities that have less tree cover and fewer parks, and areas with vegetation are cooler than areas filled with concrete.

It’s also been documented that even when you control for income, predominantly whiter communities have more green space, and Black and brown communities tend to have less green space. There's an environmental injustice there. Cities are getting hotter and hotter, and the most vulnerable individuals—the people least likely to have air conditioning—are also the ones least likely to have a park nearby to cool off in.

How can individuals protect themselves?

Keep an eye on the heat risk in your area and modify what you're doing, or at least when you're doing it, accordingly. If you're going to exercise outdoors, try to do it before the temperature gets too hot. As far as work goes, Colorado has a law to protect agricultural workers by requiring their employers to provide shade and water breaks. But not all outdoor workers—think about construction workers or roofers—have those laws in place.

If you must be out in the heat, drink lots of fluids, including electrolyte drinks. Don't drink alcohol or other things that dehydrate you. Seek shade whenever you can. And after you have been out in the hot sun, go somewhere cool – an air-conditioned restaurant, a friend’s house with air conditioning. Being able to cool your core body temperature after being out in the sun is critically important to prevent heat stroke.

How can society prepare for a hotter future?

We need to be doing everything we can to stop emitting fossil fuels to try and slow down climate change. But that's going to take a long time to have an effect.

Meantime, we need to protect people's health now and be ramping up for the fact that it's going to get worse in the future. We need to create more parks in urban areas. We need to think about shifting when the workday is and when kids practice sports in the hottest times of the year. Already, in Arizona, some construction is done at night. We need to have plans in place to help vulnerable individuals when a heat wave strikes.

How do we help the most vulnerable people?

Cooling centers are great, but you need to get the word out that they exist and you need to provide transportation to them, because a lot of the individuals who need them the most do not have their own vehicles. These centers also need to allow for pets, because people don't want to leave their pet suffering in the heat.

There's a lot of people who just don't want to go to a community cooling center, but if you said they could go to a movie theater or to the library or to the grocery store or a mall and just spend some time to cool their core body temperature down, they might go for that. There are also efforts to create networks where people check on their elderly neighbors who live alone and may be overheating and not realize it.

Most importantly, we need to recognize that extreme heat can kill, and we need to take it seriously.