Signs and Symptoms of Heat Stroke

We have all said it jokingly on a muggy summer day: "I'm going to have a heat stroke." In reality, heat stroke—and heat-related illnesses—can be a potentially dangerous part of spending time outside in the summer.

Heat stroke happens if your body temperature quickly increases to 104 degrees or more and you stop sweating. As a result, your body cannot control its temperature and cool down.

Heat stroke symptoms include central nervous dysfunction (e.g., confusion, slurred speech, and loss of consciousness), dry or sweaty skin, and a high fever. Heat stroke can cause brain damage or be deadly if untreated.

Heat stroke exists on the harmful end of a spectrum of heat-related illnesses, including heat exhaustion and cramps. Here's what you need to know about how to spot heat stroke symptoms and how they differ from other heat-related illnesses.

Central Nervous System Dysfunction

Central nervous system (CNS) dysfunction occurs when body temperature dangerously increases. With heat stroke, signs of central nervous system dysfunction include:

• Feeling confused
• Having an altered mental state
• Slurring your speech
• Losing consciousness 
• Developing seizures, in severe cases

The blood-brain barrier weakens when body temperature rises to 104 degrees. The blood-brain barrier is part of the CNS, consisting of cells and blood vessels that protect the brain from harmful pathogens. CNS dysfunction happens if that barrier breaks down.

Swelling in the brain may occur if those pathogens reach the brain and cause inflammation. The risk of brain damage increases the longer it takes the body to cool down.

Dry or Excessively Sweaty Skin

Some people with heat stroke have dry skin that is hot to the touch, while others have excessive sweating. Dry skin develops due to the body's sweating response turning off. In contrast, excessive sweating typically happens if heat stroke develops due to exercising in extreme heat.

Very High Fever

With heat stroke, the body's temperature can quickly rise to 106 degrees or higher in as little as 10–15 minutes. Sometimes, it can take days of heat exposure for a person to have heat stroke, like if you are on a long camping trip, Jazmine Oliver, MD, an internist at the Cleveland Clinic, told Health.

Heat Stroke vs. Other Heat-Related Illnesses

Heat stroke is one of the most dangerous and severe heat-related illnesses, which occurs on a spectrum.

"Heat stroke is the result on a spectrum that starts as heat exposure," Eric Goldberg, MD, an internist at NYU Langone Health, told Health. Some less severe heat-related illnesses include heat exhaustion and cramps. If untreated, both illnesses can progress to heat stroke.

Heat exhaustion symptoms include:

• Nausea
• Headache
• Irritability
• Excessive thirst but little urination
• Feeling dizzy

In contrast, one of the hallmark symptoms of heat cramps is aching muscle spasms in the abdomen, arms, or legs. You may develop heat rash, a skin irritation caused by excessive sweating and hot weather.

"Usually symptoms start very mild, [then the illness] progresses," said Dr. Oliver. "The progression is, essentially, determined by how long you're exposed to the heat." Recognizing the warning signs of other heat-related illnesses can help keep them from worsening into heat stroke. 

When To See a Healthcare Provider

Due to its severity, you must seek emergency treatment for heat stroke at the onset of symptoms, which progress quickly. If untreated, heat stroke can lead to permanent brain damage or death. 

Call 911 immediately if you are around someone experiencing heat stroke. Look for shade while you wait for an ambulance to arrive, advised Dr. Oliver. 

"Try to bring down the body temperature as quickly as possible," said Dr. Oliver. Place a cold, wet cloth or ice on the person's head, neck, armpits, and groin. Circulating air around them can help speed cooling, as well. 

In a hospital setting, healthcare providers treat people with heat stroke with intravenous (IV) fluids and cold compresses to safely bring the temperature down, said Dr. Oliver.

You can avoid heat stroke by being aware of your surroundings and listening to your body. Remember to do the following if you are outside for long periods in hot weather:

• Keep track of how long you have been in the sun.
• Wear light-colored and loose clothing.
• Do not leave children or pets unattended in a car.
• Wear sunscreen with an SPF of at least 35.
• Drink ample water or sports drinks, especially if you're working out.
• Take multiple shaded or inside breaks throughout the day.

A Quick Review

Heat stroke, the most extreme heat-related illness, happens if your body temperature quickly rises to 104 degrees. Your body's sweating mechanism stops working, so it cannot control its temperature and cool down.

Heat stroke symptoms include confusion, slurred speech, loss of consciousness, dry or sweaty skin, and a high fever. Heat stroke can cause brain damage or be deadly if untreated. Seek immediate medical attention if you or someone else displays symptoms and signs of heat stroke.