What Is Hyperthermia? Symptoms, Causes, Treatment, and Medications

Hyperthermia happens when the body gains or makes more heat than it can release. The most common cause is exposure to extreme heat, especially with physical activity or dehydration.

Environmental and Activity Causes

• Hot, humid weather or a heat wave
• Strenuous work or exercise in the heat
• Being in a hot place with poor air circulation, such as a parked car
• Dehydration and not replacing lost fluids and salts
• Wearing heavy or tight clothing in the heat

Factors That Raise the Risk

• Being very young or an older adult
• Certain chronic illnesses, such as heart, lung, or kidney disease
• Some medications, such as diuretics and certain psychiatric medicines
• Alcohol use
• Lack of acclimatization to hot conditions

A Special Cause: Malignant Hyperthermia

Malignant hyperthermia is a rare, inherited reaction to certain anesthesia drugs used during surgery. In susceptible people, these drugs can trigger a rapid rise in body temperature, muscle rigidity, a fast heartbeat, and breakdown of muscle tissue. It is a separate condition from heat stroke and is treated with the medication dantrolene.

Symptoms depend on how severe the heat illness is. Warning signs often start mild and can quickly become dangerous.

Heat Exhaustion (a warning stage) may cause:

• Heavy sweating
• Headache, dizziness, or weakness
• Nausea
• Thirst and decreased urination
• Cool, moist skin and a fast, weak pulse

Heat Stroke (a medical emergency) may cause:

• Very high body temperature (104 degrees F or higher)
• Confusion, agitation, slurred speech, or altered mental status
• Hot skin that may be dry or, with exertion, still sweaty
• Nausea and vomiting
• Rapid pulse and rapid breathing
• Seizures
• Loss of consciousness (coma)

How Long Do Hyperthermia Symptoms Last?

Mild heat cramps or heat exhaustion often improve within hours once the person cools down and rehydrates. Heat stroke is different - it can worsen within minutes and body temperature can reach 106 degrees F or higher within 10 to 15 minutes. Do not wait for heat stroke symptoms to pass; call 911 and begin cooling immediately.

Heat stroke is usually diagnosed quickly at the scene or in the emergency department based on a very high body temperature and changes in mental status after heat exposure or exertion. Rapid recognition matters because early cooling improves outcomes.

A provider or emergency team may:

• Measure core body temperature (often with a rectal thermometer for accuracy)
• Check mental status, heart rate, breathing, and blood pressure
• Ask about heat exposure, activity, fluid intake, and medications

Tests in the hospital may include:

• Blood tests to check electrolytes, kidney and liver function, and muscle breakdown (creatine kinase)
• Urine tests
• Heart monitoring (ECG)

These tests help find complications such as dehydration, electrolyte problems, kidney injury, or rhabdomyolysis (muscle breakdown).

For heat stroke, treatment is a medical emergency. Call 911 first, then begin rapid cooling while you wait for help. The main goal is to lower the core temperature as fast as safely possible, because the degree and duration of overheating drive the outcome.

Call 911 and Begin Rapid Cooling

• Move the person to a shaded or air-conditioned area and remove extra clothing
• Cool quickly using cold water immersion (an ice or cold water bath) when possible
• If immersion is not possible, wet the skin, apply cold wet cloths or ice packs to the neck, armpits, and groin, and fan the person
• Stay with the person until emergency services arrive

2. Intravenous (IV) Fluids

In the hospital or with EMS, cooled IV fluids restore hydration, support blood pressure, and help with cooling.

Supportive Hospital Care

Doctors monitor and treat complications such as electrolyte imbalances, kidney injury, and muscle breakdown. Benzodiazepines may be used to control shivering or seizures during cooling.

Milder Heat Illness

Heat cramps and heat exhaustion are treated by resting in a cool place, removing extra clothing, and slowly sipping water or an oral rehydration or electrolyte drink. Seek medical care if symptoms do not improve, if there is confusion, or if the person cannot keep fluids down.

Malignant Hyperthermia

This anesthesia-triggered emergency is treated by stopping the trigger drug, giving intravenous dantrolene sodium, cooling, and supportive care in the hospital.

Note: Fever-reducing medicines such as acetaminophen and ibuprofen do not treat heat stroke and should not replace rapid cooling.

Heat stroke can affect the whole body and can be fatal if treatment is delayed. Even survivors may have lasting effects.

Possible complications include:

• Brain damage and long-term neurological problems
• Seizures or coma
• Kidney injury or failure
• Liver damage
• Rhabdomyolysis (breakdown of muscle tissue), which can harm the kidneys
• Dangerous heart rhythm changes
• Shock and multiple organ failure
• Death, if not treated quickly

The major factor in the outcome of heat stroke is how high the temperature rose and how long it stayed elevated, which is why rapid cooling is so important.

Most heat-related illness can be prevented with simple precautions during hot weather or heavy activity.

Prevention steps include:

• Drink plenty of fluids before, during, and after activity in the heat
• Avoid strenuous activity during the hottest part of the day
• Take frequent breaks in the shade or in air conditioning
• Wear lightweight, loose, light-colored clothing
• Never leave children, older adults, or pets in a parked car
• Build up heat exposure gradually to let your body acclimatize
• Check on older adults, young children, and people with chronic illness during heat waves
• Know that some medications and alcohol raise your risk, and plan accordingly

People with a family history of malignant hyperthermia should tell their surgeon and anesthesia team before any procedure so triggering drugs can be avoided.

Heat stroke is a life-threatening emergency. Call 911 right away and begin rapid cooling if a person has a very high temperature along with confusion, agitation, slurred speech, seizures, or loss of consciousness after being in the heat.

Call 911 or seek emergency care if you notice:

• Confusion, fainting, or seizures
• Hot skin with a very high body temperature
• Repeated vomiting or inability to keep fluids down
• Symptoms that do not improve with cooling and rest

While waiting for help, move the person to a cool area, remove extra clothing, and cool them with cold water immersion or cold wet cloths and ice packs to the neck, armpits, and groin. For milder heat exhaustion that improves with rest and fluids, follow up with a provider if you have concerns, and seek care right away if symptoms worsen.

Hyperthermia and heat stroke are treated mainly with rapid cooling and IV fluids, not with pills. There is no over-the-counter medicine that treats heat stroke, and fever-reducing medicines do not lower the temperature caused by heat.

Over-the-counter products for mild heat illness and recovery:

• Oral rehydration solutions and electrolyte drinks for heat cramps or heat exhaustion
• Water and cool compresses

Prescription and hospital-administered treatments:

• Intravenous (IV) fluids given by EMS or in the hospital
• Dantrolene sodium (Dantrium) for malignant hyperthermia
• Benzodiazepines (such as lorazepam or diazepam) to control shivering or seizures during cooling

Important: Do not rely on acetaminophen or ibuprofen for heat stroke. If someone shows signs of heat stroke, call 911 and start cooling immediately - these medications are not a substitute for emergency care.