Heat Stroke

What is heat stroke?

Heat stroke is the most severe form of heat-related illness (hyperthermia). It occurs when your body overheats and can’t cool down. It can develop if you’re in a very warm space, like a home without air conditioning, or if you’re doing intense physical activity that generates lots of body heat. Heat stroke causes your body temperature to soar to dangerous levels, typically above 104 degrees Fahrenheit (40 degrees Celsius).

Untreated heat exhaustion (a moderate form of heat-related illness) can lead to heat stroke. But heat stroke can also develop without warning. Heat exhaustion and heat stroke share similar symptoms — like dizziness, nausea and weakness. But a key difference is that heat stroke causes brain dysfunction (encephalopathy). This means you experience changes to your thinking and behavior — like confusion, agitation and aggression. You may also pass out.

Heat stroke is life-threatening and requires immediate medical treatment. The longer your body temperature remains high, the greater your risk of complications (like organ damage) or death.

If you or someone around you has signs or symptoms of heat stroke, call 911 or your local emergency services number immediately.

Other names for heat stroke include:

• Sunstroke.
• Life-threatening hyperthermia.

Types of heat stroke

There are two types of heat stroke:

• Classic (non-exertional) heat stroke. Heat in your environment (like a car, home or outdoor space) overwhelms your body’s ability to cool itself. Classic heat stroke typically affects children and adults over age 65. This is the type you hear about on the news during heat waves.
• Exertional heat stroke. You generate lots of heat through physical activity (metabolic heat), and it’s more than your body can handle. Exertional heat stroke often occurs when physical activity and hot weather mix, but it can also occur in normal temperatures. This type of heat stroke typically affects young, healthy adults.

What are the signs and symptoms of heat stroke?

Heat stroke signs and symptoms include:

• High internal (core) body temperature, typically over 104 degrees Fahrenheit (40 degrees Celsius).
• Behavior changes — like agitation or aggression.
• Blurred vision.
• Confusion.
• Delirium.
• Dizziness.
• Fainting (syncope).
• Fast heart rate (tachycardia).
• Fast, shallow breathing (tachypnea).
• Low blood pressure (hypotension).
• Nausea and vomiting.
• Seizures.
• Slurred speech.
• Skin color changes — either flushed or paler than usual.
• Skin that’s dry (classic heat stroke) or sweaty (exertional heat stroke).
• Weakness.

Some of these signs and symptoms you may notice in yourself — and if you do, you should call 911 or your local emergency service number immediately. But if you’re confused or you lose consciousness, you’ll need someone else to seek medical help for you. That’s why learning the symptoms of heat stroke is so important. Bystanders are often crucial for noticing something isn’t right and alerting medical professionals.

What does heat stroke feel like?

Heat stroke involves physical symptoms like nausea, vomiting and dizziness. But it can also cause more than physical discomfort. You may feel confused or have trouble thinking clearly. Others may notice you’re not acting like your usual self. That’s because heat stroke (unlike milder forms of heat illness) affects your brain function, causing changes in your thinking and behavior.

What causes heat stroke?

Heat stroke happens when excess heat overwhelms your body’s built-in system for cooling itself. Excess heat can come from:

• Outside your body. This is environmental heat. Think of the hot, humid air that surrounds you on a summer’s day or the warm, stuffy air in an enclosed room.
• Inside your body. This is heat your metabolism generates during physical activity. It’s what you might call internal body heat.

These can occur at the same time. For example, you might go for a run on a hot day.

Normally, your body can get rid of excess heat — primarily through sweating — and restore a normal body temperature. When sweat evaporates from your skin, it cools your skin and the tissues underneath. This process is vital to thermoregulation, or your body’s ability to maintain a constant internal temperature that’s not too hot or too cold.

But if the air around you is very hot or your metabolism generates lots of heat, your body may struggle to keep up. Just like extreme heat can strain your home’s A/C unit, it can also overtax your body’s natural cooling system, leading to heat stroke.

What are the risk factors for developing heat stroke?

Heat stroke risk factors fall into several categories:

• Jobs and activities. Agricultural workers, construction workers, firefighters, military members and athletes face an increased risk of heat stroke. Casual workouts can also lead to heat stroke, especially if you’re not used to physical activity in the heat.
• Social and environmental factors. These are things like not having air conditioning at home, living in a warm climate, living alone and feeling pressure from friends or coaches to push your body to its limits.
• Age and health conditions. You face a higher risk of heat stroke if you’re over age 65, pregnant, dehydrated, have a viral or bacterial infection or have cardiovascular disease (which can affect your body’s ability to cool down). Conditions that limit your body’s ability to sweat — putting you at risk for overheating — include anhidrosis, deep burns, extensive scars and ectodermal dysplasia (an inherited condition that can affect your sweat glands).
• Medications and substances. Certain medications and substances interfere with your body’s ability to cool down. They might raise your risk of dehydration, reduce how much you sweat or cause your metabolism to generate more heat. More information is below.

Babies and children also face an increased risk of heat stroke. They’re vulnerable to extreme heat, even for short periods of time. This is why it’s dangerous to leave your child in an enclosed car, no matter how soon you think you’ll be back.

Medications and substances that raise your risk of heat stroke

Medications:

• Amphetamines.
• Anticholinergics, which are medications that block acetylcholine — a chemical that stimulates sweat production.
• Antihistamines.
• Antipsychotic medications.
• Benzodiazepines.
• Beta-blockers.
• Calcium-channel blockers.
• Diuretics.
• Laxatives.
• Lithium (a mood stabilizer).
• Selective serotonin reuptake inhibitors (SSRIs).
• Tricyclic antidepressants.

Other substances:

• Alcohol.
• Cocaine.
• Heroin.
• Phencyclidine (PCP).
• MDMA (“ecstasy”).

These lists aren’t exhaustive. Ask your healthcare provider if any medications or substances you’re using raise your risk for heat-related illness.

What are possible complications of heat stroke?

Serious complications that can occur with heat stroke include:

• Disruption to your brain activity (coma).
• Muscle breakdown, which sends toxins into your blood (rhabdomyolysis).
• Reduced flow of blood and oxygen to your organs (hypovolemic shock).
• Severe damage to major organs like your lungs (acute respiratory distress syndrome), kidneys (kidney failure), heart (heart failure) or liver (liver failure).

Because heat stroke can lead to life-threatening complications, every minute counts when it comes to getting medical care.

How is heat stroke diagnosed?

Heat stroke diagnoses usually happen in the emergency room. Providers quickly need to get a sense of what you were doing when symptoms started and what exactly you’re experiencing. They’ll check your internal (core) body temperature (typically using a rectal thermometer) and other vital signs. They’ll talk to you, if you’re able, and learn more from anyone who’s with you.

Testing to diagnose heat stroke

There’s no single diagnostic test for heat stroke. But providers can rule out other conditions with similar symptoms and check for heat stroke complications by doing:

• Blood tests.
• Urine (pee) tests.
• Electrocardiogram (EKG).
• Chest X-ray.

If providers suspect heat stroke, they’ll start treatment immediately, even if they’re still ruling out other conditions. That’s because prompt treatment is vital to survival.

What is the treatment for heat stroke?

Heat stroke treatment involves quickly cooling down your body and monitoring for complications. This requires care in an emergency room.

Call 911 immediately if you (or someone you’re with) has signs of heat stroke. But don’t wait for help to arrive to begin treating heat stroke. The sooner your body starts cooling down — ideally within 30 minutes of the start of symptoms — the better your chances of recovery.

Heat stroke first aid

Heat stroke affects a person’s ability to stay aware and awake, so they’ll likely need bystanders to help.

Here’s what you should do for someone with signs of heat stroke:

• Move the person out of the sun or heat to a cooler spot.
• Pour water over their skin and use anything available to fan them.
• Soak a towel in ice water and apply it to their skin. Cover as much of their skin’s surface area as possible. Replace with newly soaked towels every minute or so.
• Apply ice or cold packs to their armpits or neck.

It’s just as important to know what NOT to do. Here are key tips:

• Don’t give the person fever-reducing medication, like acetaminophen. These medications don’t help heat stroke, which happens for different reasons than a fever. They may also worsen complications like organ damage.
• Don’t give them any fluids to drink. This might seem surprising. But a person experiencing heat stroke might accidentally inhale the liquid (aspiration), which can be dangerous.

Treating heat stroke at the hospital

Healthcare providers in the emergency room focus on cooling your body until it gets to a safe temperature. Common methods for cooling include:

• Cold water immersion. This is usually used for exertional heat stroke rather than classic heat stroke. A provider dunks your entire body (except your head) in cold water or ice water. Heat leaves your body and enters the surrounding water.
• Misting and fanning. This is often used for classic heat stroke but can be suitable for either type. A provider sprays as much of your skin as possible with water while large fans circulate the air around you. As the water evaporates from your skin, your body temperature lowers.

Providers will closely monitor you for signs of complications and give you further treatment as needed. This might include:

• IV fluids (through a vein).
• Intubation.
• Medications to support organ function.

You’ll need to stay in the hospital — possibly the intensive care unit — until providers determine it’s safe for you to go home.

Can heat stroke be prevented?

Yes, it’s often possible to prevent heat stroke. This can be harder to do if you have certain risk factors, but a little planning can go a long way. Here are some suggestions:

• Keep your home cool. Use fans and/or air conditioning. When the temperature is very high — especially above 99 degrees Fahrenheit (37.2 degrees Celsius) — fans won’t be enough.
• Develop a plan for hot days. If your home isn’t cool enough, identify places where you can go to cool down. These include community centers, shopping malls, movie theaters and loved ones’ homes.
• Stay hydrated. Drink plenty of water before, during and after physical activity in the heat. Make sure you also take in electrolytes — for example, by adding electrolyte powders or tablets to your water. It’s important to stay hydrated even if you’re taking it easy, too. Your healthcare provider can advise you on how much water to drink to support your body’s needs.
• Avoid or limit heat exposure. Try to schedule workouts at cooler times of the day (like early morning). On hot days, opt for an indoor workout in air conditioning. If you must exert yourself in the heat — for example, for work — talk to your employer about scheduled breaks and ways to lower the risk of heat-related illness.
• Acclimatize. This is a fancy word that simply means giving your body time to adjust to the heat. A coach or trainer can help you develop a plan that’s right for you. In general, you’ll start with shorter workouts in the heat and gradually make them longer and more intense.

What is the outlook for people with heat stroke?

Your outlook depends on many factors, including:

• How soon treatment begins.
• How long your core temperature is elevated.
• How many organs are damaged and the extent of damage.
• Your underlying medical conditions and overall health.

With prompt treatment, you may recover with little or no damage to your organs or body functioning. But heat stroke can be fatal. Your care team can tell you what you might expect in your situation.

Long-term effects of heat stroke

Some people have lingering effects for weeks or months after having heat stroke. These include:

• Trouble coordinating your muscle movements (cerebellar ataxia).
• Slurred speech or trouble speaking so others can understand you (dysarthria).
• Trouble forming new memories (anterograde amnesia).

It’s also possible to have problems with organ function that last for years. This can raise your risk of other health problems. Your healthcare provider can tailor treatments, support and resources to your needs.