Hyperthermia: Cause, symptoms, treatment & prevention

Hyperthermia refers to a group of heat-related conditions characterized by an abnormally high body temperature. It is an umbrella term which refers to several conditions that can occur when your body’s heat-regulation system can’t handle the heat in your environment.

Hyperthermia differs from fever in that the body’s temperature set point remains unchanged. The opposite is hypothermia, which occurs when the temperature drops below that required to maintain normal metabolism.

In humans, core body temperature ranges from 95.9°F to 99.5°F during the day, or 35.5°C to 37.5°C. In contrast, people with some level of hyperthermia have a body temperature of more than 100.4°F (38°C).

Causes of hyperthermis

Main causes of hyperthermia include:

Heat stroke: Occurs when thermoregulation is overwhelmed by a combination of excessive metabolic production of heat (exertion), excessive environmental heat, and insufficient or impaired heat loss, resulting in an abnormally high body temperature. In severe cases, temperatures can exceed 40 °C (104 °F). Heat stroke may be non-exertional (classic) or exertional.

  • Exertional:

Significant physical exertion in hot conditions can generate heat beyond the ability to cool, because, in addition to the heat, humidity of the environment may reduce the efficiency of the body’s normal cooling mechanisms. Human heat-loss mechanisms are limited primarily to sweating (which dissipates heat by evaporation, assuming sufficiently low humidity) and vasodilation of skin vessels (which dissipates heat by convection proportional to the temperature difference between the body and its surroundings, according to Newton’s law of cooling). Other factors, such as insufficient water intake, consuming alcohol, or lack of air conditioning, can worsen the problem.

The increase in body temperature that results from a breakdown in thermoregulation affects the body biochemically. Enzymes involved in metabolic pathways within the body such as cellular respiration fail to work effectively at higher temperatures, and further increases can lead them to denature, reducing their ability to catalyse essential chemical reactions. This loss of enzymatic control affects the functioning of major organs with high energy demands such as the heart and brain.

  • Situational

Situational heat stroke occurs in the absence of exertion. It mostly affects the young and elderly. In the elderly in particular, it can be precipitated by medications that reduce vasodilation and sweating, such as anticholinergic drugs, antihistamines, and diuretics. In this situation, the body’s tolerance for high environmental temperature may be insufficient, even at rest.

Heat waves are often followed by a rise in the death rate, and these ‘classical hyperthermia’ deaths typically involve the elderly and infirm. This is partly because thermoregulation involves cardiovascular, respiratory and renal systems which may be inadequate for the additional stress because of the existing burden of aging and disease, further compromised by medications. During the July 1995 heatwave in Chicago, there were at least 700 heat-related deaths. The strongest risk factors were being confined to bed, and living alone, while the risk was reduced for those with working air conditioners and those with access to transportation. Even then, reported deaths may be underestimates as diagnosis can be misclassified as stroke or heart attack.

Read Also: Heat Cramps: Symptoms, Causes, Treatments & First aid

Drugs: Some drugs cause excessive internal heat production.The rate of drug-induced hyperthermia is higher where use of these drugs is higher.

  • Many psychotropic medications, such as selective serotonin reuptake inhibitors (SSRIs), monoamine oxidase inhibitors (MAOIs), and tricyclic antidepressants, can cause hyperthermia. Serotonin syndrome is a rare adverse reaction to overdose of these medications or the use of several simultaneously. Similarly, neuroleptic malignant syndrome is an uncommon reaction to neuroleptic agents. These syndromes are differentiated by other associated symptoms, such as tremor in serotonin syndrome and “lead-pipe” muscle rigidity in neuroleptic malignant syndrome.
  • Various stimulant drugs, including amphetamines and cocaine, and hallucinogenic drugs, including PCP, LSD, and MDMA can produce hyperthermia as an adverse effect.
  • Malignant hyperthermia is a rare reaction to common anesthetic agents (such as halothane) or the paralytic agent succinylcholine. Those who have this reaction, which is potentially fatal, have a genetic predisposition.
  • The use of anticholinergics, more specifically muscarinic antagonists are thought to cause mild hyperthermic episodes due to its parasympatholytic effects. The sympathetic nervous system, also known as the “fight-or-flight response”, dominates by raising catecholamine levels by the blocked action of the “rest and digest system”.
  • Drugs that decouple oxidative phosphorylation may also cause hyperthermia. From this group of drugs the most well-known is 2,4-dinitrophenol which was used as a weight loss drug until dangers from its use became apparent.

Personal protective equipment: Those working in industry, in the military, or as first responders may be required to wear personal protective equipment (PPE) against hazards such as chemical agents, gases, fire, small arms and improvised explosive devices (IEDs). PPE includes a range of hazmat suits, firefighting turnout gear, body armor and bomb suits, among others. Depending on design, the wearer may be encapsulated in a microclimate, due to an increase in thermal resistance and decrease in vapor permeability. As physical work is performed, the body’s natural thermoregulation (i.e., sweating) becomes ineffective. This is compounded by increased work rates, high ambient temperature and humidity levels, and direct exposure to the sun. The net effect is that desired protection from some environmental threats inadvertently increases the threat of heat stress.

The effect of PPE on hyperthermia has been noted in fighting the 2014 Ebola virus epidemic in Western Africa. Doctors and healthcare workers were only able to work for 40 minutes at a time in their protective suits, fearing heat stroke.

Other causes: Other rare causes of hyperthermia include thyrotoxicosis and an adrenal gland tumor, called pheochromocytoma, both of which can cause increased heat production. Damage to the central nervous system from brain hemorrhage, status epilepticus, and other kinds of injury to the hypothalamus can also cause hyperthermia.

Read Also: Difference between Heat exhaustion and Heat stroke

Risk factors of hyperthermis

It often occurs during physical exertion or exercise in a warm or humid environment. During exercise, blood pressure rises to deliver more oxygen to working tissues, increasing body temperature and the amount of work the body must do to maintain a stable temperature.

When combined with other factors, such as warm weather that also raises the body temperature and reduces its ability to release heat, it is unsurprising that exercise can increase the likelihood of overheating.

Though less common, hyperthermia can also take place while someone is resting, especially during extreme heat waves. Those on certain medications, diets, and with some medical conditions can also be affected by hyperthermia even when they are at rest.

Children and older adults are at increased risk as well. Many kids play hard in the hot outdoors without taking time to rest, cool off, and stay hydrated. Older adults tend to be less aware of temperatures changes, so they don’t often respond in time if their environment heats up. Older adults who live in a home without fans or air conditioning may also face hyperthermia in extremely hot weather.

General risk factors of hyperthermia include:

  • Immune conditions
  • Heart conditions
  • Blood pressure or circulation conditions
  • Lung, kidney, and liver conditions
  • Dehydration, especially chronic dehydration
  • Metabolic conditions
  • Diabetes
  • Sweat gland or sweating conditions
  • Obesity
  • Excessive alcohol intake
  • Smoking
  • Being underweight
  • Gastroenteritis
  • Diuretic medications, usually for high blood pressure or conditions, such as glaucoma and edema
  • Medications for the central nervous system, including antihistamines, antipsychotics, and beta-blockers
  • A low sodium diet or low salt diet
  • Illicit drug use, particularly synthetic marijuana


Types of hyperthermia and their associated symptoms

The symptoms of hyperthermia depend on the stage it has reached or how much the body is overheated. Symptoms of overheating may develop very quickly or over the course of hours or days.

In general terms, the symptoms of hyperthermia depends on the type that develops; here we will consider the types of hyperthermia together with the symptoms

Heat stress

If your body temperature starts to climb and you’re unable to cool yourself through sweating, you’re experiencing heat stress. Heat stress can lead to serious complications, such as heat exhaustion and heat stroke.

In addition to feeling uncomfortably hot, you may also experience:

  • Dizziness
  • Weakness
  • Nausea
  • Thirst
  • Headache

If you’re feeling signs of heat stress, get to a cooler area and rest. Start drinking water or other fluids with electrolytes that will help restore hydration. Electrolytes are substances in the body, such as calcium, sodium, and potassium that keep you hydrated. They help regulate your heart rate, nerve function, and muscle health.

If your symptoms worsen, seek medical attention.

Read Also: Chilblains – Cause, Symptoms & Prevention tips

Heat fatigue and cramps


  • Excessive sweating
  • Exhaustion
  • Flushed or red skin
  • Muscle cramps, spasm, and pain
  • Headache or mild light-headedness
  • Nausea

Heat exhaustion

Heat exhaustion, if left untreated, can lead to heat stroke, which is a life-threatening condition.


  • Cold, pale, wet skin
  • Extreme or heavy sweating
  • Fast but weak pulse
  • Nausea, vomiting, and diarrhea
  • Headache
  • Muscle cramps
  • Exhaustion
  • Weakness
  • Intense thirst
  • Dizziness
  • Less frequent urination and dark urine
  • Difficulty paying attention or concentrating
  • Mild swelling of the feet and ankles or fingers and hands
  • Temporarily fainting or losing consciousness

Heat syncope

Syncope, also known as fainting, occurs when your blood pressure drops and blood flow to the brain is temporarily reduced.

It tends to happen if you’ve been exerting yourself in a hot environment. If you take a beta-blocker to lower your blood pressure, you’re at greater risk for heat syncope.

Fainting is often preceded by dizziness or lightheadedness. You may feel close to fainting, but if you relax and cool down quickly, you may prevent actually losing consciousness. Putting your legs up can help.

As with other heat-related illnesses, rehydrating is key. Any fluid will do, but water or electrolyte-filled sports drinks are best.

Heat edema

Heat edema can occur if you stand or sit for a long time in the heat and are not used to being in warmer temperatures. This can cause your hands, lower legs, or ankles to swell.

This swelling is from fluid buildup in your extremities. This is possibly related to a response involving the aldosterone-stimulated reabsorption of sodium into the blood through the kidneys.

Usually heat edema spontaneously subsides over time once you become used to the warm environment. Cooling down and putting your feet up will also help, as will staying hydrated with adequate water and electrolyte intake.

Heat rash

Sometimes, being active in the heat for prolonged periods of time can cause red pimple-like bumps to appear on the skin. This usually develops underneath clothing that has become soaked with sweat.

Heat rash typically disappears on its own after you cool down or change clothes.

However, infection is possible if the skin isn’t allowed to cool soon after the rash has appeared.

Heat stroke

Without treatment, heat stroke can lead to dangerous complications, especially in young children, those whose immune system is compromised, and people over 65 years of age.

With heat stroke the body temperature is more than 103°F to 104°F, depending on a person’s normal, average body temperature.

Temperature and many of the other early signs of heat stroke are the same as those for heat exhaustion.


  • Fast, strong pulse or very weak pulse
  • Fast, deep breathing
  • Reduced sweating
  • Hot, red, wet, or dry skin
  • Nausea
  • Headache
  • Dizziness
  • Confusion
  • Disorientation
  • Blurred vision
  • Irritability or mood swings
  • Lack of coordination
  • Fainting or losing consciousness
  • Seizure
  • Organ failure
  • Coma
  • Death

Hyperthermia Diagnosis

Hyperthermia is generally diagnosed by the combination of unexpectedly high body temperature and a history that supports hyperthermia instead of a fever. Most commonly this means that the elevated temperature has occurred in a hot, humid environment (heat stroke) or in someone taking a drug for which hyperthermia is a known side effect (drug-induced hyperthermia). The presence of signs and symptoms related to hyperthermia syndromes, such as extrapyramidal symptoms characteristic of neuroleptic malignant syndrome, and the absence of signs and symptoms more commonly related to infection-related fevers, are also considered in making the diagnosis.

If fever-reducing drugs lower the body temperature, even if the temperature does not return entirely to normal, then hyperthermia is excluded.

Managing hyperthermia

A person should immediately stop what they are doing and move to a cool, shaded place with good airflow if they suspect hyperthermia.

People should seek medical attention if heat cramps last longer than one hour after they have rested in a cool place.

Medical attention should also be sought for general symptoms that do not improve within 30 minutes of rest and care.

Additional tips for treating mild to moderate hyperthermia include:

  • Sipping cool water or an electrolyte drink
  • Loosening or removing excess clothing
  • Lying down and trying to relax
  • Taking a cool bath or shower
  • Placing a cool, wet cloth on the forehead
  • Running the wrists under cool water for 60 seconds
  • Not resuming activity until symptoms have gone away
  • Placing ice packs or compresses under the arms and groin
  • Using a fan to cool the skin

How to prevent hyperthermia

The first step is recognizing the risks in working or playing in extremely hot conditions. Being in the heat means taking the following precautions:

  • Take cool-down breaks in the shade or in an air-conditioned environment. If you don’t need to be outside in extreme heat, stay indoors.
  • Stay well hydrated. Drink water or drinks containing electrolytes, such as Gatorade or Powerade, every 15 to 20 minutes when you’re active in the heat.
  • Wear lightweight, light-colored clothing when outdoors.
  • If your home isn’t well air-conditioned, consider spending time in an air-conditioned mall, library, or other cool public place during hot spells.

By Ubong Edet

A passionate Health and Safety professional with a good level of field experience and relevant certifications including NEBOSH, OSHA, ISO, etc certifications. An Health and Safety activist who believes in the growth and continual improvement of the profession. He is going all out to create awareness and safe precious lives.

One thought on “Hyperthermia: Cause, symptoms, treatment & prevention”
  1. I appreciate your article on hyperthermia. We talk a great deal on hypothermia but not hyperthermia. At Help-A-Heart CPR here in San Antonio, Texas we offer Advanced First Aid classes and instruct students on the dangers of heat stroke and hyperthermia due to our incredibly hot summers in South Texas.

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