Heat Exhaustion vs. Heatstroke: What’s the Difference?

Both heat exhaustion and heatstroke are serious conditions. They are types of heat illness—medical conditions that result from the body’s inability to control its core body temperature after exposure to high temperatures and dehydration (fluid loss with insufficient replacement).

Heat exhaustion causes general muscle weakness, excessive sweating, nausea, vomiting, and fainting. Heatstroke occurs when the body’s internal temperature reaches over 103 degrees Fahrenheit and a person has changes in consciousness and behavior, sweats excessively, and experiences nausea and/or vomiting.

Symptoms of both heat exhaustion and heatstroke should be taken seriously. It is also important to understand what type of symptoms you are experiencing and how to prevent them. This article will discuss heat exhaustion vs. heatstroke, including symptoms, causes, risk factors, treatment, and prevention.  

Person experiencing heat illness

 Terry Vine / Getty Images

Symptoms of Heat Exhaustion vs. Heatstroke

Some symptoms of heat exhaustion and heatstroke are similar, but these conditions are also very different. It is important to know that while heat exhaustion isn’t as severe as heatstroke, it shouldn’t be taken lightly because it can easily progress to heatstroke.  

Heat Cramps

Heat cramps are the earliest signs of a heat illness. They are painful muscle spasms that occur when someone has become dehydrated and has lost nutrients and minerals (electrolyte loss) from excessive sweating. Heat cramps are commonly felt in the arms, legs, back, and abdomen.  

Heat cramps are caused by heat, illness, and activity. They can come on suddenly or gradually. They often start as muscle twitches and are unnoticeable until they become severe.

Heat Exhaustion Symptoms

Heat exhaustion occurs after a person has been exposed to high temperatures and is experiencing dehydration.  

According to the Centers for Disease Control and Prevention (CDC), the most common signs of heat exhaustion are:

  • Heavy sweating
  • Cold, pale, and clammy skin
  • A fast or weak pulse
  • Nausea and/or vomiting
  • Muscle cramps
  • Weakness or fatigue
  • Dizziness
  • Headache
  • Fainting or near fainting

Additional symptoms might include dark yellow urine (a result of dehydration) and confusion. 

Heatstroke Symptoms 

Heatstroke is the most serious form of heat illness and is considered a medical emergency. It often occurs after milder heat illnesses, including heat cramps, heat syncope (fainting), and heat exhaustion. It can also occur in people who have no previous signs of heat illness.  

Heatstroke results when there is prolonged exposure to high temperatures in combination with dehydration. This leads to a failure in the body’s internal temperature control. Heatstroke occurs when the body’s temperature reaches 104 degrees.

Having that high core body temperature affects the central nervous system, causing the following symptoms:

  • Nausea and vomiting
  • Headache
  • Seizures (uncontrolled electrical activity in the brain)                                                                                                      
  • Confusion and disorientation
  • Loss of consciousness or coma 

Additional symptoms of heatstroke include:

  • Dry skin that doesn’t sweat or profuse sweating
  • Dizziness
  • Low urine output
  • Rapid breathing or fast heart rate
  • Weakness

Causes of Heat Exhaustion and Heatstroke

One study showed an average of over 60,000 cases of heat illness per summer seen by emergency departments in the United States. The study showed about 12% of the people affected were admitted to the hospital (an average of 7,678 per year) and there were an average of 46 deaths per year.

The causes of heat exhaustion and heatstroke are similar. The leading cause of both conditions is the body’s inability to cool itself due to hot weather, exercise, or both.  

Additional causes are dehydration, alcohol use, and overdressing.

Body’s Failure to Cool Itself

When your body’s internal temperature is not regulating correctly, your body can become unable to cool itself. Being in a hot environment can lead to a rise in your core body temperature after exposure to hot and humid weather for a long period. This is most common in older adults and people with chronic conditions.

Strenuous activity can increase the body’s core temperature, especially if you exercise or work outside in hot weather or a hot room. This often affects people not used to high temperatures or who are not staying hydrated in hot areas.  

Dehydration  

Dehydration refers to the absence of sufficient fluids in the body. Heat exposure combined with dehydration often leads to heat illness. 

Alcohol Use  

Drinking alcohol when out in high temperatures can lead to the body not being able to regulate its body temperature. Alcohol combined with hot temperatures can also lead to dehydration. This is because alcohol is a diuretic and in combination with heat, it can cause you to lose body fluids through sweating and urination.

Overdressing  

It is important to wear clothing that is suitable for extreme heat. Clothing weights, fabrics, and even color affect sun penetration and how well air circulates over your skin, allowing for sweat to evaporate. When sweat cannot evaporate from the skin, body temperature increases.

Risk Factors for Heat Exhaustion

Anyone can experience heat exhaustion, but certain risk factors can make some groups of people more vulnerable to heat exhaustion.

Age

Infants, young children, and older adults are at an increased risk for heat exhaustion. This is because of their inability to regulate their body temperatures. They are also more likely to become easily dehydrated when out in the heat.  

Drug Use

Some medications can increase your risk for heat exhaustion. This is because they can cause dehydration. Examples of medications that increase the risk for heat exhaustion are those used to treat migraines, allergies, bipolar disorder, seizures, and high blood pressure.

Obesity  

People who are affected by excess weight might be at an increased risk for heat exhaustion. This is because obesity and related health conditions, such as diabetes, affect the way the body regulates its core temperature. Being overweight can also cause the body to retain more heat.

Sudden Temperature Changes  

People who are not used to hotter climates are more vulnerable to heat exhaustion, regardless of age or health status. This is because the body needs time to get used to the higher temperatures.  

Older people, those with chronic medical conditions, and those taking medicines that interfere with body temperature are most affected when exposed to sudden temperature changes. They are the most at risk for heat exhaustion when traveling to hot climates or dealing with extreme weather changes.

High Heat Index  

Heat exhaustion is often related to the heat index—a measurement of how heated the body gets from the effects of humidity and air temperature. Excessive humidity can also hinder sweat evaporation and affect the body’s ability to cool itself.

The risk for a heat-related illness increases when the heat index is at 90 degrees or higher. It is important to pay attention to the heat index during the summer months. The heat index can be even higher when you are in the sunlight.

People who do not have access to air-conditioning in their workplaces or their homes due to cost or other reasons are at greater risk when the heat index is high. They may need to access public spaces that are cooled or cooling shelters during times of high heat.

Heatstroke as a Complication of Heat Exhaustion

Heat exhaustion by itself isn’t usually a major problem. However, if it is untreated and ignored, it can lead to heatstroke.  

Heatstroke is much more serious than heat exhaustion. It can damage the brain, heart, liver, and kidneys through hyperthermia (when the body’s heat-regulating mechanisms aren’t working well).

Even a single episode of hyperthermia can lead to prolonged or permanent neurological or cognitive dysfunction (impairments in nerve function, thinking, and memory). If heatstroke becomes severe, it can lead to death.

When to See a Healthcare Provider

If you think you might be experiencing heat exhaustion, you should stop what you are doing and rest. Move indoors or to a shady area and drink cool water or a sports drink.  

Seek medical attention for signs of heat exhaustion that do not improve within an hour of starting fluids and resting. Get immediate help if you, or someone else:

  • Cannot keep fluids down
  • Develop a fever of 103 degrees or higher
  • Have trouble speaking, standing, or walking
  • Are sweating excessively
  • Become confused or lose consciousness

Diagnosing Heat Illness

Heat illnesses are generally diagnosed based on their symptoms.  

With heat exhaustion, a healthcare professional will start by checking your temperature. You will be asked what you were doing before coming into the emergency room and what symptoms you are experiencing.

Because heatstroke is a dangerous condition, people who experience it should call 911 or be brought to an emergency room. At the emergency department, your temperature will be taken.

You will also have tests done to check organ function, blood tests, urine tests, and other testing the healthcare provider thinks might be helpful.

If it is determined you do not have heatstroke, they will look for other causes of symptoms. If it is heatstroke, you might be admitted to the hospital for treatment or you will receive treatment in the emergency room. 

Treatment for Heat Exhaustion  

Treatment for heat exhaustion usually does not require emergency or other medical care. However, if you experience symptoms of heat exhaustion, you must get out of the heat, preferably to an air-conditioned space. Find a cool and shady location to rest if you cannot get indoors.  

Try to drink plenty of cool liquids, especially sports drinks, to replace lost electrolytes. You should avoid caffeine and alcohol because both increase the risk of dehydration.

Other things you can do to manage heat exhaustion are:

  • Remove tight or excess clothing.
  • Take a cool bath or shower.
  • Use a fan.
  • Apply cold compresses to the neck and underarms to help cool the body.

Call your healthcare provider if these measures do not help and symptoms don’t improve after about an hour. If symptoms get worse, call 911 or go to an emergency room.  

Treatment for Heatstroke

Heatstroke requires urgent medical treatment. If you are waiting for an ambulance or transporting someone to an emergency room, it is important to cool the affected person as much as possible.

Steps to take include:

  • Applying ice packs to the armpits, groin, and neck
  • Drinking sports drinks or salted water
  • Laying down in a cool area, with feet slightly elevated
  • Removing clothing that is tight or heavy

At the hospital, treatment for heatstroke might include:  

  • Cooled intravenous (IV) fluids
  • IV fluids to manage dehydration
  • Cooling blankets
  • Ice bath
  • Antiseizure medicines
  • Supplemental oxygen

In severe cases, cold-water lavage might be needed. This treatment uses catheters (thin, flexible tubes) to fill body cavities (down the throat or in the rectum) with cold water. The goal is to lower your body temperature.  

The time you spend in the hospital will depend on how severe your heatstroke is and if there is any organ or neurological involvement.

Preventing Heat Exhaustion and Heatstroke

There is an increased risk for heat illness when people are out in hot weather or while exercising. Fortunately, there are things you can do to prevent heat exhaustion and heatstroke.  

Wear Light, Loose Clothing  

It is important to make good clothing choices when out in hot weather to prevent heat illness. Wearing clothing that is lightweight and loose helps to draw sweat away from the skin. Wearing a wide-brimmed can offer sun protection for your head and face.  

Prevent Sunburn  

Sunburn is sometimes associated with heat exhaustion and heatstroke. This is because sunburns affect the body’s ability to cool itself and can lead to the loss of fluids.

Ways to protect yourself from sunburn include using sunscreen, wearing protective clothing, and staying indoors in the middle of the day when the sun’s rays are the strongest.

Stay Hydrated  

While outdoors in the heat, make sure you are drinking plenty of fluids. Don’t wait until you are thirsty to drink. Avoid beverages that could cause you to become dehydrated, including sugary, alcoholic, and caffeinated beverages. 

Use Caution With Some Medications

If you are taking medications that might increase your risk for dehydration, it is even more important to take precautions to avoid heat illness. This can include wearing sunscreen, staying indoors on hot days, and drinking plenty of fluids.

Never Leave Anyone in a Parked Vehicle

You should never leave a child or a pet in a parked car. Before leaving your car, be sure to check that everyone is out.  

Cars can quickly heat up in very hot temperatures even with windows cracked open. Anyone who is left in a hot car—especially children—is at risk for heatstroke.

Rest During Hot Times  

It is a good idea to limit outdoor activities for times of the day when it is cooler, like early morning and in the evening.  If you are out during hot times of the day, try to rest often in shady areas or indoors so that your body can recover from the effects of the heat.  

Be Careful If You’re at Risk

If you are someone who takes medications or has a medical condition that increases your risk for heat illness, it is important to limit your time outdoors when the heat index is higher.

If you are outdoors and notice signs of overheating, take action right away to keep things from getting worse. This includes going indoors, drinking fluids, and finding ways to cool your body.  

Get Acclimated to Weather

If you are not used to higher temperatures, limit your time outdoors until you acclimate to the higher temperatures. If you are not used to the heat, you are more likely to experience a heat illness. It might take some time to get used to the hotter temperatures, so be sure to pace yourself.  

Summary

Heat exhaustion and heatstroke are two types of heat illness. They can be very serious conditions. Heat exhaustion causes muscle cramping, excessive sweating, nausea, and vomiting, and sometimes, fainting.

Heatstroke occurs when the body’s core temperature reaches over 103 degrees. A person with heatstroke might experience a loss of consciousness, seizures, and confusion.  

If you develop heat exhaustion, you should get out of the heat as quickly as possible and drink cool fluids to bring down your body temperature. If you continue to feel sick or think you might be experiencing heatstroke, call 911. Heatstroke is a medical emergency and can become life-threatening very quickly.

A Word From Verywell

People who experience heat exhaustion or heatstroke need to cool their bodies down quickly to improve their outlook. How long it takes to recover from a heat illness depends on your overall health, age, and how quickly you cool down or receive medical care.  

If you experience heatstroke, do not delay treatment. Once you have recovered, it is important to check with your doctor about when it is safe for you to return to work and do regular activities.

Frequently Asked Questions

  • What is the main difference between heat exhaustion and heatstroke?

    Unlike heat exhaustion, heatstroke requires you to seek immediate medical attention. This is because the body’s internal temperature reaches 103 degrees, which can lead to serious and permanent neurological and organ damage.

  • Which is worse heat exhaustion or heatstroke?

    Heatstroke is a more severe condition, but heat exhaustion can quickly turn into heatstroke if left untreated and the body’s temperature continues to rise. 

  • What are three signs of heat exhaustion?

    Common signs of heat exhaustion are heavy sweating, muscle cramps, and dehydration.

  • How do you know if you have heatstroke?

    The main symptom of heatstroke is a high core body temperature. Additional, more noticeable signs include increased sweating, lack of sweating, flushed skin, rapid breathing, a racing heart rate, fainting, dizziness, and severe headache.

  • How long do you feel bad after heat exhaustion?

    Most people can fully recover from heat exhaustion within a day or two. Recovery time often depends on how quickly you cooled down, your overall health, and your age.

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