Heat exhaustion occurs when your body loses excess amounts of water and salt, typically from sweating. On the other hand, heat stroke is a serious medical emergency that occurs when your body is unable to control its internal temperature.

As the weather gets warmer, we tend to spend more time outside under the hot sun. It’s important to know the difference between heat stroke and heat exhaustion.

Knowing the signs and symptoms of these two conditions could save your life or that of a loved one.

Symptoms related to heat stroke or heat exhaustion can be very serious. Developing muscle cramping may be the first indication that you’re developing a heat-related illness. Other symptoms include:

Heat exhaustion symptomsWhat to doHeat stroke symptomsWhat to do
general weaknesstake a cool shower or use a cold compress to decrease body temperatureelevated body temperature above 104°F (40°C)call 911 for emergency treatment
increased heavy sweatinghydrate with water or sports drinksrapid and strong pulse or heart ratemove to a shaded or cool area
a weak but faster pulse or heart ratemove to a shaded or cool arealoss or change of consciousnesscirculate air to speed up cooling
nausea or vomitingseek medical treatment if vomiting continueshot, red, dry, or moist skinuse a cold compress or cold, wet cloth to help lower body temperature
possible fainting, lightheadedness, dizzinesslie down
pale, cold, clammy skinremove any extra layers or unnecessary clothing, like shoes or socks

Keep in mind that heat stroke can be much more serious than heat exhaustion and requires immediate medical attention to prevent complications.

Both heat stroke and heat exhaustion are caused by your body’s inability to cool itself.

Sweat is your body’s natural tool for cooling you down. If you overexercise or work strenuously in hot weather or a heated room, your body may have difficulty producing enough sweat to keep you cool.

Other causes of heat exhaustion and heat stroke include:

  • dehydration
  • wearing heavier, tight clothing
  • consuming alcohol

If you’re experiencing heat exhaustion for an extended period of time, it can lead to heat stroke. Heat stroke can come on quickly if it’s very hot or you’re overexerting yourself. That’s why it’s important to begin treatment at the first signs of heat exhaustion.

Certain factors can increase your risk for heat exhaustion and heat stroke, though anyone can develop either condition.

The following factors can increase your risk for heat sensitivity:

  • Age. Infants and children under the age of 4 and adults aged 65 and older are at increased risk for heat-related illnesses. That’s because your ability to regulate temperature is more difficult at these ages.
  • Prescription medications. Some medications used to treat high blood pressure or heart conditions may reduce your ability to stay hydrated. Dehydration can cause heat exhaustion and heat stroke.
  • Obesity. Your body retains more heat when you weigh more. It can also be more difficult to cool your body down if you have overweight or obesity.
  • Sudden temperature changes. When you rapidly move from a colder to a warmer climate, like going on vacation in a hotter location, your body may not be able to adjust to the warmer weather. You may have more difficulty regulating your body temperature as a result.
  • A high heat index. Heat index is a measurement that factors in humidity along with the outside temperature to determine how hot it feels to you and your body. If the humidity is high, your sweat evaporates less easily, and you may have a harder time cooling yourself down. If the heat index is greater than 91°F (32.8°C), you should focus on prevention methods.

If you’re experiencing any symptoms of a heat-related illness, you should take your temperature. A temperature above 100°F (38°C) may indicate heat exhaustion while a temperature above 104°F (40°C) is a sign of heat stroke.

Seek medical attention immediately if you believe you’re having a heat stroke. Your doctor will likely be able to diagnose heat exhaustion or heat stroke based on your symptoms, but they may decide to run tests to confirm the diagnosis or check for complications:

  • A blood test may be used to check your sodium or potassium levels to help determine if you’re dehydrated.
  • A sample of your urine may be taken. Dark yellow urine may be a sign of dehydration.
  • Muscle function tests may be performed.
  • Your doctor runs tests to check your kidney function.
  • X-rays and other imaging tests can be used to determine if you have any internal organ damage.

If you’re able to cool down within 30 minutes, heat exhaustion isn’t typically considered an emergency.

But if you’re unable to lower your body temperature or if you experience any of the following symptoms, you should call 911 and seek immediate medical attention:

If you begin experiencing symptoms of heat exhaustion, try to find a cooler location if possible. For example, if you’re outside, look for a shady area. If you’re indoors, remove a layer of clothing or turn on the air conditioning.

You may also want to lie down, or if that isn’t possible, stop doing any strenuous activities. That may help your body regulate temperature.

Drink water or a sports drink to help rehydrate yourself. Sports drinks have electrolytes, which your body loses through excessive sweating.

If you’ve become nauseated or vomit, seek help from a medical doctor right away.

A heat stroke is considered a medical emergency. Call your local emergency services immediately if you suspect that you’re having a heat stroke.

Your doctor may place you in a bath of cold ice water to lower your temperature quickly. They may also mist your skin with water, pack you in ice packs, or wrap you in a special cooling blanket.

If the cold causes you to shiver, your doctor may give you medications to stop the shivering. This might increase your body temperature.

With treatment, you can fully recover from heat exhaustion. Early intervention can also stop it from progressing to heat stroke.

Experiencing a heat stroke is an emergency. If left untreated, it can cause damage to your:

  • heart
  • kidneys
  • muscles
  • liver
  • lungs
  • brain

Your risk for serious complications, including death, increases the longer treatment is delayed.

One of the main ways to prevent heat-related illnesses like heat exhaustion and heat stroke is to keep your body temperature cooler. This is particularly important when you’re working or doing activities outside in the heat or sun.

Here are some prevention tips:

  • Stay hydrated. Drink two to four cups of water every hour that you’re doing activities outside in the heat or direct sun. Your body needs more water than usual when working in a hot environment because you’ll lose more fluids through sweating.
  • Avoid alcohol or caffeinated beverages if you’re doing strenuous activities, especially in the heat. The caffeine increases your risk for dehydration.
  • On hotter days, try to do more activities inside in a temperature-controlled or air-conditioned environment.
  • Try to avoid doing activities outside during the hottest parts of the day and in direct sunlight.
  • Wear light-colored, loose, lightweight clothing when doing activities outside in the heat. A wide-brimmed hat will keep sun from your face and help you stay cooler.
  • Take cooler baths or showers on a hot day to help cool you down.
  • Take frequent breaks when working or exercising in the heat. This includes activities like hiking or playing sports.
  • Never leave children, infants, adults, or pets in a closed, parked car. The temperature inside a closed car can become very hot, even if the temperature outside is mild. That can lead to heat-related illnesses.

Planning for hot weather activity ahead of time can help reduce your risk of heat exhaustion and heat stroke.