Heat Exhaustion vs. Heat Stroke: Why You Can’t Afford to Miss the Difference

When you’re outdoors in the hot summer months, it’s common to feel a little overheated. Most of the time you’ll feel better when you find some shade, drink something cool, and rest for 10 to 15 minutes. 

Your body has systems in place to regulate your temperature and keep you safe. But those systems can be overwhelmed when you can’t get out of the heat. As the thermometer rises, heat exhaustion and heat stroke are more likely. In this article we’ll discuss these serious and potentially life-threatening conditions. And we’ll go over what you can do if heat-related illness affects you or someone else.

Which is more serious: Heat stroke or heat exhaustion?

Heat stroke and heat exhaustion are both heat-related illnesses, but they are at different points on the spectrum. Heat exhaustion is easier to treat and may not always need professional medical care. Most people will make a quick recovery by simply getting into a cooler environment and hydrating. 

Heat exhaustion can progress to heat stroke. So heat stroke is more serious. It’s a life-threatening condition that needs immediate medical attention. It can result in serious injury to vital organs — like the brain, heart, liver, and kidneys. And without treatment, heat stroke can lead to death for more than half of the people who develop it.  

What causes heat stroke and heat exhaustion?

Even though heat exhaustion and heat stroke are different conditions, the factors that cause them are the same. We’ll review the common causes of heat-related illness here.

Physical exertion in the heat 

High demands on your body in hot environments can lead to both heat exhaustion and heat stroke. Activities that may put you at risk include:

• Sports

• Hiking

• Construction work

• Agricultural work

• Yard work

• Military exercises

• Indoor work in hot environments

Prolonged heat exposure

Whether inside or outside, certain groups of people have a higher risk for heat-related illness. These risk factors include:

• Very young age, especially babies

• Older age (over 65)

• Higher amount of body fat

• Overactive thyroid

• Heart disease

• Diabetes

• Sickle cell disease

Medications and substances

People who take certain medications or substances are at increased risk for heat illness. Examples include:

• Beta blockers

• Diuretics (“water pills”)

• Some antidepressants, especially ones in the tricyclic family

• Certain medications for schizophrenia, including olanzapine and chlorpromazine

• Allergy and sleep medications that have diphenhydramine (Benadryl)

• Amphetamines (including medications for attention-deficit disorder)

• Cocaine

• Alcohol (when you drink alcohol and are exposed to heat)

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Regardless of your health conditions or fitness level, you’re at higher risk for heat-related illness if:

• The environment is both hot and humid

• You’re not acclimated to the heat for at least 1 week before heavy outdoor activity

• You’re dehydrated

So how hot does it need to be for heat exhaustion and heat stroke to happen? That depends on two things: 

1. How well you’re acclimated: If you live in a hot environment, after a few days your body may be able to adjust to higher temperatures. 

2. Humidity: Even temperatures around 80°F can be risky if the humidity levels are very high. 

But regardless of humidity, any time the thermometer reaches 100°F or higher, the risk rises for all of us.

Symptoms of heat stroke vs. heat exhaustion

In the summer months, most people feel overheated from time to time. But how do you know when it’s more than simply feeling hot? 

Signs of heat exhaustion

If you’re wondering whether you or someone near you is experiencing heat exhaustion, here are a few things to look for:

• Heavy sweating 

• Weakness and feeling tired

• Achy muscles

• Fast or weak pulse

• Dizziness

• Headache

• Nausea

• Fainting or feeling like you might pass out

Feeling dizzy or lightheaded is common with heat exhaustion. But if someone starts to act confused or disoriented, that is the telltale sign of heat stroke.

Signs of heat stroke

The signs of heat stroke can be a lot like heat exhaustion. But you only need one of these extra signs to meet the definition of heat stroke:  

• Confusion

• Body temperature over 104°F

• Seizures

• Hot, red skin (may be dry or damp)

Although it’s a common belief that if you’re sweating you don’t have heat stroke — this is not true. Some people with heat stroke continue to sweat. 

When should you go to the hospital for heat exhaustion?

You can often treat mild heat exhaustion outside of a hospital. But heat stroke is a medical emergency that needs urgent care. If there are any signs of confusion or loss of consciousness, the best course of action is to call 911. 

Treatment for heat exhaustion

If someone is feeling overheated but they’re alert and making sense, the following steps will help them recover from their heat exhaustion:

• Get out of the heat and into a cooler environment. 

• Hydrate with cool fluids. 

• Apply ice packs or cold towels on the neck, groin, underarms, and scalp (this may help speed up recovery).

Seek immediate medical attention if they:

• Have symptoms that get worse 

• Develop vomiting, extreme drowsiness, or confusion

• Do not feel better within 1 hour

• Have a temperature over 104°F

Treatment for heat stroke

Heat stroke has a death rate of over 50% without prompt treatment. So if you’re concerned about someone, the first step is to call 911. And if you’re not sure whether you’re dealing with heat exhaustion or heat stroke, it is best to err on the side of safety and get urgent medical attention.

While waiting for the ambulance to arrive, there are things you can do to help cool them down:

• Remove the person’s outer layers of clothing.

• Spray them down with a cool liquid (if available).

• Apply ice packs to the neck, underarms, groin, and scalp.

• Do not give them anything to drink. They’re likely too weak to swallow properly, and the fluid could go into their lungs and affect their breathing.

• Do not give them aspirin or other medications. Heat stroke can affect blood clotting, and medications like aspirin may make that worse.

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Written by:

Sarah A. Samaan, MD

Sarah Samaan, MD, FACC, FACP, FASE is a board-certified cardiologist who practiced clinical cardiology for nearly 30 years. She is a member of the American College of Cardiology and the American College of Physicians, among others.

Edited by:

Katie E. Golden, MD

Katie E. Golden, MD, is a board-certified emergency medicine physician and a medical editor at GoodRx.

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