How to prevent heat exhaustion: A science-backed guide

From the desk of
Robb Wolf
ScienceHow to prevent heat exhaustion: A science-backed guide

Today I’ll be talking about a form of heat illness called heat exhaustion. Although heat exhaustion isn’t typically life-threatening, it precedes a condition that is life-threatening: heat stroke. 

That’s right, heat illnesses exist on a spectrum, which affords us time to reverse their progression. This means you can stop exercising, get indoors, enjoy a bit of air conditioning, and rehydrate with water and electrolytes. And thankfully, heat exhaustion is also fairly easy to prevent with some simple planning.

This article will cover heat exhaustion prevention and treatment. I’ll also cover causes, symptoms, who’s at risk, and how it differs from heat stroke. Let’s start by adding some color to that last point.

Heat Exhaustion vs. Heat Stroke

Heat stroke is the life-threatening progression of heat exhaustion. When someone sufferers from heat stroke, their core body temperature typically rises above 104℉.

Heat stroke explains why heat is the number one cause of weather-related deaths in the US. There are two types: classic and exertional. Classic heat stroke carries a staggering mortality rate of 10-65%, as it is often suffered by older adults due to impaired sweating. Low blood pressure and significant tachycardia (rapid heart rate) despite low exertion are both indicative of classic heat stroke, and are signs that you should seek medical attention.

Exertional heat stroke, on the other hand, is only fatal 3-5% of the time as it tends to affect people whose bodies are better-equipped to cool down. This overheating is not just due to the climate, but also overexertion and oftentimes inadequate or ineffective hydration methods. With proper cooling techniques, researchers believe exertional heat stroke deaths in young adults may even be 100% preventable.

Unlike heat stroke, heat exhaustion generally resolves without complications. The key is to take action before it escalates to heat stroke. Both conditions share many symptoms, so it’s important to be able to recognize the warning signs.

Next: a rundown on the symptoms of heat exhaustion—your indicators to intervene.

Symptoms of Heat Exhaustion

People may experience heat stress when spending too much time in hot environments or over-exerting themselves. If external factors exceed a person’s ability to dissipate heat, you have a recipe for heat exhaustion.

The symptoms of heat exhaustion include:

  • Nausea
  • Vomiting
  • Dizziness
  • Light-headedness
  • Irritability
  • Headache
  • Tiredness
  • Thirst
  • Weakness
  • Excessive sweating
  • Less pee
  • Muscle cramps

According to survey data, the most common symptoms of heat exhaustion are headache, fatigue, or some combination thereof. In addition, body temperature tends to be elevated—but typically below 104℉. 

Some level of heat stress can actually be beneficial. Regular sauna users, for instance, have been shown to have improved cardiovascular and immune health and lower mortality from heart disease. One explanation? Temporary heat exposure mimics exercise by increasing heart rate and raising core body temperature. But as with exercise, too much heat for too long can be harmful.

Fortunately, the prognosis for heat exhaustion is good. Most people fully recover after escaping the heat, getting some rest, and replacing fluids and electrolytes. But if core body temperature keeps rising, you may enter heat stroke territory.

Heat Exhaustion Risk Factors

Heat exhaustion occurs when the body can’t shed heat to keep core temperature between 97.7 and 99.5℉. A variety of factors contribute to overheating: climate, activity, and a person’s individual characteristics. 

#1: Climate

When the temperature gets into the 100s, self-cooling mechanisms (i.e., sweat) often fail. That’s why you see so many heat-related incidents during heat waves.

Humidity, breeze, and sun exposure also play a role. A humid, breezeless, sunny day will cause more heat stress than a dry, windy, cloudy one. Weather apps often adjust for these elements by offering a “real feel” temperature estimate. When in doubt, plan by whichever figure is higher—that way you’re always prepared.

#2: Activity Level

The more you exert yourself, the hotter your body will get. And you don’t need 100+ temps to feel exertional heat stress. A hard workout in the 80s might do it. How you’re feeling is paramount, so pay attention to your body.

#3: Individual Factors

Finally, don’t forget a person’s individual characteristics. These include:

  • Age. Seniors, children, and infants are at greater risk than most because they often have more difficulty self-cooling. As we grow older, our body’s heat tolerance decreases and we sweat less, so our core body temperature rises more quickly.
  • Medications. Blood pressure medications, anti-inflammatories, beta-blockers, calcium channel blockers, and other drugs can decrease heat tolerance.
  • Sweat volume. This varies by individual. 
  • Clothing. More layers make it harder to stay cool.
  • Diseases or conditions. Diabetes, infections, heart disease, and skin disorders can hamper self-cooling.
  • Alcohol consumption. Heat and alcohol often don’t play well together.
  • Hydration status. Dehydration and electrolyte imbalances don’t cause heat stress per se, but they will worsen matters. 

Staying hydrated is a unique challenge for older folks in particular. There are interesting studies on older generations’ misperceptions of proper hydration, including less awareness of the need for electrolytes and the dangers of overhydration. They may also contend with impaired thirst mechanisms and mobility issues that hinder access to fluids.

Consequently, you should pay special attention to your wiser loved ones during a heat wave. Let’s talk about heat stress prevention now.

How To Prevent Heat Exhaustion

Preventing heat exhaustion is mostly common sense. Stay cool, stay hydrated, and don’t overexert yourself. Let’s double-click on these tactics.

#1: Stay cool

The simplest way to prevent heat exhaustion is to avoid the heat. I know this statement sounds head-slappingly obvious, so I won’t spend too much time on it.

The air conditioner is your friend. Ensure your car and home A/C are functioning and ready to rock. If your A/C breaks in a heat wave, borrow some cool air by visiting a family member or friend, or hit your local mall, gym, or coffee shop.

If you are exercising outside, take regular breaks to rest and cool down with an ice-cold towel, fan, or misting spray.

#2: Be wise with exercise

I’ve never been a big treadmill guy. I prefer exercising outdoors for the mental and physical health benefits, but I do modify my plans in hot weather. I used to live in Texas (yee haw!), and when I saw 110-degree days in the forecast, I moved my training indoors. I still took walks, but I saved the intense stuff for the A/C.

I suggest you do something similar. Can you move your tennis match to a slightly cooler day? Can you jog at 7 AM instead of 3 PM? Can you prioritize indoor training during a heat wave? All of these moves will help prevent heat exhaustion.

#3: Hydrate properly

One sign of heat stress is excessive sweating. Your body pumps out sweat to keep you cool. But heavy sweating, of course, means heavy losses of both fluids and sodium. Both need to be replaced to prevent dehydration and all the symptoms that come along with it.

Here’s the thing. Water and electrolyte losses don’t cause heat stress, but they often accompany and exacerbate it. And like heat stroke, severe dehydration and electrolyte imbalances can land someone in the hospital.

It’s crucial to replace both water AND electrolytes. If you rehydrate with too much plain water (as many people do), you’ll dilute blood sodium levels and cause more problems. That’s why we include 1000 mg of sodium in every stick of LMNT. It’s the only electrolyte drink mix with enough sodium to move the needle, and it tastes fantastic with zero added sugar. Just ask my kids!

#4: Adjust to the heat gradually at first

Heat acclimation is a process of exposing the body to heat over a period of days or weeks. It leads to adaptations such as increased sweating, decreased sweat sodium concentration, improved temperature regulation, better fluid balance, and cardiovascular stability. All of these adjustments mean greater tolerance for the sweltering heat, and therefore better physical performance on hot days.

Heat acclimation protocols typically entail 4–14 consecutive days of running or cycling efforts (between 30 and 90 minutes) in temperatures greater than 86 °F, but passive methods like sauna work too. Nearly complete adaptation can be achieved in 7–10 days, but even 4–6 days can bring significant benefits. If you stop training in a hot environment, the adaptations decay over time. However, re-acclimation can be achieved more rapidly than starting from scratch.

Hydration is crucial during heat acclimation, as increased sweating requires adequate fluid and electrolyte replacement. Take individual factors into account when designing your heat acclimation program – the point is to adapt gradually and stay safe in the heat.

Treating Heat Exhaustion

If you suspect that you’re experiencing heat exhaustion, follow the common-sense measures listed above. Get to a cool place, grab an ice-cold towel for your neck, rest, and rehydrate with fluids and sodium.

Severe cases of heat exhaustion may require medical attention. For instance, if someone is too queasy for oral rehydration, they may need intravenous fluids and electrolytes.

Remember, it’s a short hop from heat exhaustion to heat stroke. Do everything you can to prevent that graduation, and keep an eye on your loved ones.

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