What is Hyperthermia? Symptoms, Causes, and Treatments You Need to Know

Heat-related illnesses aren't something to ignore.

Though it's usually welcomed after long winters, summertime—and the hot temperatures that come with it—can pose some pretty significant health risks. If you are planning to be outside during excessive heat, it's essential to educate yourself about heat-related illnesses, commonly known as hyperthermia.

Hyperthermia - Young fitness woman resting after workout in nature
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Overall, "extreme heat is defined as summertime temperatures that are much hotter and/or more humid than average," the Centers for Disease Control and Prevention (CDC) explains on its website. The agency also says that "humid and muggy conditions can make it seem hotter than it really is," and that there's no set standard for what's considered excessive heat, because some places are hotter than others, and higher-than-normal temperatures are measured by what's considered average for a particular area.

Here's what you need to know about hyperthermia in the summertime, including what the symptoms of heat illnesses are, and how you can prevent and treat them.

What Is Hyperthermia?

Hyperthermia is a catch-all phrase for heat-related illnesses, according to the National Institutes of Health (NIH). The agency adds that, in general, hyperthermia is "an abnormally high body temperature caused by a failure of the heat-regulating mechanisms of the body to deal with the heat coming from the environment."

It's the opposite of hypothermia, a condition in which the body loses heat faster than it can produce heat, leading to a dangerously low body temperature, per the CDC.

"Hyperthermia occurs when core body temperature is markedly elevated or above 40 C (104 F)," Sara Hogan, MD, former health sciences clinical instructor at UCLA's David Geffen School of Medicine at UCLA and dermatologist at UCLA Medical Center, Santa Monica, tells Health. "Hypothermia occurs when core body temperature is 35 C (95 F) or lower, often when body heat is lost to a cold environment."

The most commonly known forms of hyperthermia or heat-related illness—which exist on a spectrum include heat fatigue, heat syncope, heat cramps, heat exhaustion, and heat stroke. Some forms of hyperthermia—like heat exhaustion and heat stroke—are worse than others.

"Depending on how high your body temperature gets, there is a risk it can become life-threatening," Ula Hwang, MD, an emergency medicine doctor at Yale Medicine and professor at Yale School of Medicine, tells Health.

In these cases, a person's body temperature rises faster than it can cool itself down—up to 106 F or higher—which can cause damage to the brain and other vital organs, per the CDC.

While hyperthermia is most commonly associated with exposure to outdoor heat on a very hot, humid day, or over-exerting yourself in high temperatures, Dr. Hwang adds that it can also occur while "being indoors in an extremely hot room for a long time."

Most at Risk Group

"The elderly are most vulnerable to heat-related illnesses," Alexa Mieses Malchuk, MD, MPH, an Assistant Professor in the Department of Family Medicine Physician at the University of North Carolina School of Medicine, tells Health. "Because as we age our bodies naturally sweat less, we may have blood that doesn't circulate throughout our body as well, and we may take some medications like water pills or diuretics that make it harder to sweat."

There are also a number of chronic conditions—such as heart, kidney, or lung disease—that can make you more susceptible to complications from hyperthermia.

Dr. Malchuk adds that other risk factors for hyperthermia include not drinking enough water, living in an overheated space without air conditioning, lack of mobility, overdressing, overcrowded spaces, and having any sort of cognitive impairment that may interfere with your ability to respond to hot weather (for example, advanced brain disorders like dementia). Those who perform strenuous exercise outside in hot temperatures are also more susceptible to heat-related illnesses, though this is most common in younger people.

Symptoms of Hyperthermia

Because hyperthermia includes all heat-related illnesses, the signs and symptoms are varied. According to the CDC, the symptoms of the different types of hyperthermia include:

Signs of Heat Stroke

  • An extremely high body temperature (above 103°F)
  • Red, hot, and dry skin (no sweating)
  • Rapid, strong pulse
  • Throbbing headache
  • Dizziness
  • Nausea
  • Confusion
  • Unconsciousness

Signs of Heat Exhaustion

  • Heavy sweating
  • Paleness
  • Muscle cramps
  • Tiredness
  • Weakness
  • Dizziness
  • Headache
  • Nausea or vomiting
  • Fainting

Signs of Heat Cramps

  • Muscle pain or spasms in the abdomen, arms, or legs.

Signs of Heat Rash

  • Red clusters of pimples or small blisters on the neck, chest/underneath the breasts, groin, or elbow creases

Tips on Prevention and How It Is Treated

Fortunately, hyperthermia can be easily avoided and many cases can be treated without long-term complications.

"Hyperthermia can be prevented by wearing lightweight clothing, staying hydrated, seeking shade, and taking time to rest in hot weather," says Dr. Hogan.

"If you must be outside, stay in cooler and shaded places (use an umbrella) and wear light-colored clothing," adds Dr. Hwang.

However, If you suspect that someone is suffering from a heat-related illness, NIH suggests taking the following steps for treatment:

  • Get the person out of the heat and urge them to lie down in a shady area, air-conditioned, or in other cool places.
  • Encourage the individual to shower, bathe or sponge off with cool water.
  • Apply a cold, wet cloth to the wrists, neck, armpits, and/or groin.
  • If the person can swallow safely, offer fluids such as water or fruit and vegetable juices, but avoid alcohol and caffeine.

More severe forms of hyperthermia, like heat stroke, can also be fatal. If heat stroke is suspected, the NIH suggests seeking immediate emergency medical attention by calling 911.

"Once the person is in medical care, treatment techniques vary but can include immersion in cold water, cooling blankets, or intravenous fluids to address dehydration," says Dr. Hwang.

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