What Is Hypothermia?

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Hypothermia (low body temperature) refers to both a medical condition and a symptom of cold exposure. It occurs when the body falls below a certain temperature and cannot warm itself. Normal body temperature is considered 98.6 degrees. Hypothermia is considered anything below 95 degrees. Left untreated, hypothermia can become a medical emergency.

The integumentary system (skin) helps to regulate body temperature by controlling heat loss. The body generates heat through cellular metabolism, which is a fancy way of saying that living—at least in a human—keeps us warm.

As long as our bodies can generate at least as much heat as we lose, we maintain our core temperature. If we lose more than we make, we suffer from hypothermia.

What Is Hypothermia?
Verywell / Emily Roberts

Types of Hypothermia

There are three general types of accidental hypothermia:

  1. Acute exposure to cold, such as immersion in cold water or getting caught in the snow. This is worse than simply being out in cold weather.
  2. Fatigue or other lack of metabolic action that doesn't produce sufficient heat, including intoxication with alcohol or malnutrition.
  3. Chronic exposure to mild or moderate cold temperatures without a break. Even chatting too long outside without a jacket on a cool autumn evening is enough to develop mild hypothermia, even though it is also easily treated.

Hypothermia is also very common during surgery, which is due to a combination of a cold environment and compromise of the skin (since by definition the skin has been cut open) allowing heat to escape more rapidly than normal. Perioperative hypothermia is well documented and surgeons are looking for ways to prevent it while still providing an environment that is healthy and comfortable for the surgical team.


Humans have known for millennia that exposure to the cold could result in death and that fatigue or exhaustion make it worse. To actually define and recognize hypothermia, a thermometer small enough to be used regularly on humans was required. It was invented in 1866 and not widely available for medical use until decades later. It took a long time after thermometers became available to get an idea of how warm the body should be.

A lot of people had to have their temperatures taken and recorded to find out what normal was. And, all of the temperatures had to be taken the same way—standardization that didn't exist for many years. The first study of human temperatures was published in 1868 and it included a discussion of temperatures for more than 25,000 subjects with various diseases. Most of the temperatures were taken under the arm (midaxillary), a notoriously inaccurate method.

Even in the early years of using temperature as a diagnostic tool, doctors knew that patients couldn't handle low temperatures, but the condition didn't have a proper name. The term "hypothermia" didn't appear in print until about 1880 and was used to mean different things, from having cold hands to not being "tolerant" of the cold. It wasn't clearly defined as doctors know it today until the 20th century.

It was well-known that hypothermia (despite not having an actual name) could be caused by exposure to the cold, and the role of alcohol intoxication in hypothermia was identified right away. The idea that hypothermia could occur during surgery is a relatively modern realization.

Hypothermia Symptoms

The signs and symptoms of hypothermia depend on the severity of the condition. At first, there is only shivering and a generally uncomfortable feeling. The patient might have fumbling fingers.

As it progresses, hypothermia causes increasing trouble with fine motor skills, fatigue, confusion, loss of consciousness, and eventually death.


Hypothermia is caused by losing more heat than the body can generate. The most common cause of hypothermia is exposure to a cold environment. A cold environment doesn't necessarily mean the outdoors; those under anesthesia may be more prone to hypothermia because of altered thermoregulatory mechanisms. Other causes or risk factors include trauma or surgical wounds, fatigue, and alcohol intoxication. For babies, sleeping in cold bedrooms can be a risk factor.


Getting a diagnosis of hypothermia requires taking an accurate temperature that is below a certain threshold. A combination of the actual temperature and the signs and symptoms of the patient determines whether the hypothermia is considered mild, moderate, or severe.


Preventing hypothermia requires conserving more heat than the patient loses through the skin. Treating hypothermia uses the exact same techniques as those used to prevent hypothermia, but results in heat transferring into the body rather than stopping the loss of heat.

A Word From Verywell

In most cases, preventing or treating hypothermia can be done simply as long as a patient is identified as being in a cold environment and then the patient is either removed from the cold environment (goes inside on a chilly night) or precautions are taken to trap heat in the body (blankets, gloves, jackets, and a cup of hot cocoa).

Mild hypothermia is not really a big deal unless it goes unrecognized, but it's extremely important not to underestimate moderate or severe hypothermia. Shivering is good. It means that hypothermia is still in the mild stage and can be easily reversed. Once shivering stops, you must take the situation seriously and take steps to conserve whatever heat the patient has left and then begin the process of rewarming.

Cold and dry is better than cold and wet. If a patient is soaked, they are losing heat 25 times faster than if they are dry. Peel off the wet clothes. It might seem counter-intuitive to remove clothing from a severely cold patient, but getting them out of wet clothes and wrapped in something dry could save a patient's life. 

6 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Infographic: Avoid Spot Treat: Frostbite & Hypothermia. Centers for Disease Control and Prevention

  2. Hart SR, Bordes B, Hart J, Corsino D, Harmon D. Unintended perioperative hypothermia. Ochsner J. 2011;11(3):259-70.

  3. Guly, H. History of accidental hypothermia. Resuscitation, 2011;82(1):122-125. doi:10.1016/j.resuscitation.2010.09.465

  4. Mackowiak P, Worden G. Carl Reinhold August Wunderlich and the Evolution of Clinical ThermometryClinical Infectious Diseases. 1994;18(3):458-467. Retrieved May 17, 2020

  5. Brandt S, Mühlsteff J, Imhoff M. Diagnosis, prevention and treatment of accidental and perioperative hypothermia. Biomedizinische Technik/Biomedical Engineering. 2012;57(5). doi:10.1515/bmt-2012-0016

  6. Hart SR, Bordes B, Hart J, Corsino D, Harmon D. Unintended perioperative hypothermia. Ochsner J. 2011;11(3):259-70.

Additional Reading
Rod Brouhard, EMT-P

By Rod Brouhard, EMT-P
Rod Brouhard is an emergency medical technician paramedic (EMT-P), journalist, educator, and advocate for emergency medical service providers and patients.