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  3. Hypothermia


  1. What is hypothermia?
  2. Symptoms
  3. Causes
  4. Diagnosis
  5. Treatment
  6. Prevention
  7. FAQs

What is hypothermia?

Hypothermia occurs when the body starts losing heat faster than it can produce, leading to a number of potentially dangerous symptoms. The definition of hypothermia is the body’s core temperature dropping below 35 degrees Celsius or 95 degrees Fahrenheit.[1] Hypothermia is a life-threatening condition and, if suspected, medical attention should be sought immediately.

Symptoms of hypothermia depend on the temperature to which the body’s core drops: the lower the body temperature, the more serious the condition is for the person affected.[2] A person with hypothermia, who may need urgent medical help, could have the following symptoms:[3][4]

  • A shiver
  • Pale skin in adults and bright red skin in infants
  • Tiredness and confusion
  • Slow and shallow breath
  • A weak pulse
  • Irrational behaviour

Hypothermia is usually caused by exposure to cold weather conditions. However, it can sometimes occur due to other medical conditions such as sepsis or stroke.[2] Those who spend prolonged periods outside and older people in badly-heated homes are among the most at risk of a dangerous drop in body core temperature.

Treatment for hypothermia revolves around warming up the affected person. Steps to keep warm before an ambulance arrives include very gently moving the person inside, if outdoors, and covering them in blankets.

The best approach to avoiding hypothermia caused by cold exposure is making sure to keep warm. This usually comes with good preparation, such as choosing appropriate clothing if cold weather is forecast and making sure a home is well heated and insulated.

Stages and symptoms of hypothermia

The symptoms of hypothermia depend on how cold the body’s core temperature is.If hypothermia is suspected, seek medical attention immediately.[5]

The condition can progress through four stages of severity, each with a slightly different cluster of symptoms:

Stage one: mild hypothermia

Mild hypothermia occurs when the body’s core temperature is between 35 degrees Celsius (95 degrees Fahrenheit) and 32 degrees Celsius (89.6 degrees Fahrenheit). Symptoms of mild hypothermia include:[2][5]

  • Shivering
  • Faster heart beat
  • Faster breathing
  • A pale body that is cold when touched
  • Dizziness and tiredness
  • Some loss of physical coordination

Stage two: moderate hypothermia

A person progresses into moderate hypothermia when their body temperature drops below 32 degrees Celsius (89.6 degrees Fahrenheit), to as low as 28 degrees Celsius (82.4 degrees Fahrenheit). Symptoms of moderate hypothermia include:[2][5]

  • Slower heart beat
  • Slower breathing
  • Lower blood pressure
  • Less shivering than before
  • Loss of bladder control
  • Increased confusion
  • Delirium, e.g., restlessness, abnormal behaviour, incoherence
  • Loss of ability to focus or pay attention
  • Slower reflexes

The abnormal behaviour and lack of physical awareness caused by hypothermia may lead to actions that can make symptoms worse. For example, some people with the condition have been known to begin removing clothing even though weather conditions remain cold.

Stage three: severe hypothermia

Once a person’s body core temperature drops below 28 degrees Celsius (82.4 degrees Fahrenheit), they begin to experience severe hypothermia. Symptoms at this stage include:[2][5][6]

  • Loss of consciousness and, potentially, coma
  • A weak or abnormal pulse
  • Weak breathing
  • Extremely cold skin
  • Dilated pupils

Stage four: no vital signs

The fourth stage of hypothermia is reached if the body’s core temperature drops below 24 degrees Celsius (75.2 degrees Fahrenheit). A person with stage four hypothermia may appear to be dead, with no heartbeat or pulse. It may still be possible to revive some people in this stage.

Hypothermia causes

Hypothermia is caused by the body losing more heat than it is producing. There are four major ways the body can lose heat:[5][^9)

  • Radiation, which is heat loss into the surrounding atmosphere
  • Conduction, which is heat loss to an object or surface that is cooler than the body
  • Convection, which is heat loss caused by air or wind passing across the skin, e.g. wind or a desk fan
  • Evaporation, which is caused by body fluid on the skin turning into vapour, e.g. through sweating

Some of the initial symptoms of hypothermia are a response to the body losing heat. Shivering, for example, can increase the amount of heat generated by the body.

If hypothermia occurs simply because of the environment the person is in, such as a badly-heated home or after falling into cold water, then it is described as primary hypothermia. Secondary hypothermia is heat loss caused by, or made worse by, another medical condition.

People spending long periods outside without proper protection from the weather, such as the homeless, are most at risk of being affected by hypothermia. There is a particular danger for those drinking alcohol or using other sedative drugs outdoors as these substances can make hypothermia more likely.[7]

Primary hypothermia

Some of the ways primary hypothermia could potentially be caused include:[4][8]

  • Spending too long in cold weather, e.g., getting stuck in a blizzard
  • Immersion in cold water, e.g., falling into a lake
  • Not wearing adequate clothing, e.g., going outside without a winter coat
  • Wearing wet clothing, especially in windy conditions
  • Badly-heated indoor environments, e.g., houses with no heating or insulation

Secondary hypothermia

Secondary hypothermia is when another condition affects the body’s ability to regulate its temperature. This is of particular danger when a person is in some of the cold environments, such as those listed above. However, secondary hypothermia can also occur in mild weather. The conditions that cause hypothermia do one of the following :[2][9]

  • Increase heat loss, such as burns, psoriasis and other skin conditions. Substances and conditions which cause the dilation of blood vessels are also included in this category
  • Decrease heat production, such as hypothyroidism, hypoglycemia, malnutrition and some neuromuscular disorders
  • Damage the ability to regulate body temperature, such as strokes, Parkinson’s disease, brain tumours, sepsis and head or spine trauma

Hypothermia can also be caused as a side-effect of certain medications or drugs that can lower body temperature, such as beta-blockers, meperidine, clonidine, phenothiazines.

As well as the homeless, people at particular risk of secondary hypothermia include the elderly and those involved in accidents causing bodily trauma. One example of the latter would be a person in a car crash waiting a long time for the emergency services to arrive.

If you regularly feel cold and cannot find the cause, try a symptom assessment on the Ada app.

Alcohol and hypothermia

The warming effect of alcohol makes it tempting to drink some when the weather is cold. However, alcohol warms up the skin by taking away heat from the body’s core. Combined with intoxication, this makes drinking alcohol particularly dangerous when temperatures are low.

One example of a dangerous situation is a person slipping due to intoxication and falling onto a cold floor. A person who may be affected by hypothermia should not drink any alcohol.[10]

Neonatal hypothermia

Newborn babies have less control than the general population over the regulation of heat in their bodies. This is especially true of smaller newborns, such as those born prematurely or who are underweight. Medical professionals will generally take several steps to ensure that a child is kept warm after birth to prevent hypothermia developing.[11] These steps can include making sure that the birth room temperature is above 25 degrees Celsius (77 degrees Fahrenheit) and wrapping babies in warmed blankets after birth.

Hypothermia for cardiac arrest

In targeted temperature management (TTM), previously known as therapeutic hypothermia, doctors intentionally reduce the body’s core temperature as a form of medical treatment. This has been shown to be an effective way to both protect the brain and improve survival following cardiac arrest.[12]

Diagnosing hypothermia

Several tests are run to ensure a correct diagnosis of hypothermia.

Physical examination and patient history

The patient’s physical symptoms will be examined and the doctor will try and gain as much information as possible on potential causes of hypothermia and the period of time that the person has been affected.[13] The doctor will also be looking for any underlying medical conditions that may be a factor.

Core temperature test

A person’s core temperature will need to be measured. This is usually done with a special thermometer. The thermometer will be inserted rectally, or into the esophagus via the mouth, to ensure an accurate core temperature reading.[2][14]


A medical professional will test the heart’s rhythm and electrical activity with an electrocardiogram (ECG). This test will be run to analyse how much the heart has been affected by hypothermia. An ECG involves electrodes being attached to the torso and to the limbs.

Read more about electrocardiogram tests »

Other tests

A number of blood tests can be run to check which parts of the body have been negatively affected by hypothermia. Depending on the cause of the condition, a doctor may run imaging scans, such as an X-Ray or a computed tomography (CT) scan.

Hypothermia treatment

If hypothermia is suspected, emergency services should be contacted immediately. Both first-aid treatment and hospital treatment of hypothermia are geared towards warming up the affected person.

Hypothermia first aid

If the person affected has severe hypothermia and is already unconscious, both their breathing and their pulse should be monitored. During hypothermia, both these vital signs can become incredibly weak, so the pulse should be checked for at least one minute before, if possible, beginning cardiopulmonary resuscitation (CPR).[5]

If already conscious or if consciousness is regained, then the following steps can help while waiting for the emergency services:[5][6]

  • Move the person to a warm environment, but be careful to be gentle
  • Remove any wet clothing, cutting it off, if possible, to avoid unnecessary movement[15]
  • Make sure the person is as dry as possible
  • Protect the person from wind or breezes
  • Warm the person with an electric blanket if one is available. Alternatively, cover the person in layers of blankets and sheets
  • Use skin-to-skin contact to share body heat
  • Keep monitoring the person’s pulse and breathing
  • Hot water bottles, warmed towels or hot compresses are useful. To warm up the body’s core, place these on the torso and in the armpits and groins. Try not to make them too hot as it increases the possibility of burns
  • Keep the person hydrated with non-alcoholic and non-caffeinated beverages

Avoiding cardiac arrest and other possible risks of hypothermia

There are several mistakes that can be made when treating a person with hypothermia, which could have dangerous consequences. This means being very careful and gentle when giving first aid. For example, moving a person with moderate to severe hypothermia too quickly increases the risk of cardiac arrest, also known as hypothermia shock. Other mistakes to avoid include:[5][6]

  • Placing the person in a bath
  • Leaving the person alone
  • Massaging or rubbing the person
  • Allowing the person to exert themselves too much physically
  • Allowing the person to drink or giving them alcohol

Hypothermia hospital treatment

The protocol followed by doctors treating hypothermia is to stabilize the person and then take steps to warm their core temperature. In cases of severe or life-threatening hypothermia, emergency treatment could include:[13][16]

  • Using a tube to aid breathing
  • Inserting warmed fluids into the body using an intravenous drip
  • Administering warmed oxygen

The way in which medical professionals choose to warm a person with hypothermia up depends on the severity of their condition. Rewarming techniques are divided into three categories: passive, active external and active internal.[17][7]

Passive rewarming

Passive rewarming techniques are similar to those used in first aid and are helpful for people with mild hypothermia. The affected person will be covered in blankets or other types of insulation. Doctors will maintain a warm room temperature of around 28 degrees Celsius (82.4 degrees Fahrenheit). The aim is to get the person’s own body to start warming itself up.

Active external rewarming

Moderate cases of hypothermia may be treated using active external rewarming. Heat sources such as warmed blankets and heat packs will be placed close to the person’s body. Doctors will focus on heating the torso first as heating the body uniformly can release cold blood that was previously stuck in the arms and legs. This runs the danger of inadvertently lowering the person’s core temperature.

Active internal rewarming

In more severe cases of hypothermia, warmed fluids and gases are inserted into the body in an attempt to achieve rewarming. The IV drips and heated oxygen given as part of emergency treatment are included in this category. Other active internal rewarming techniques include washing out organs and the space between organs with warmed saline solution.

Extracorporeal blood rewarming is the fastest method of rewarming the body, but it is not available in many hospitals. In this treatment, blood is extracted from the circulatory system before being heated and then returned into the body.

Hypothermia prevention

The best way to avoid primary hypothermia is to keep as warm as possible. Most of the time, this comes down to preparation and being wary of cold environments.

Hypothermia in cold weather

Some workers will need to spend a lot of time in cold weather, such as those who have to work outside. Other people may choose to do so as recreation, such as mountaineers or hikers. Ways they can protect themselves from the cold include:[18][19]

  • Wearing appropriate clothing, such as waterproofs if rain is forecast and multiple layers if it is cold
  • Wearing loose layers of clothing as this increases warmth
  • Wearing a hat, scarf and gloves or mittens
  • Avoiding spending prolonged periods outside alone
  • Bringing along a buddy to recognize the signs of hypothermia
  • Going inside for breaks wherever possible
  • Eating warm, high-carbohydrate foods such as noodle soups and pasta dishes for a quick energy hit
  • Bringing food with high fat and protein content along if spending a lot of time outside
  • Drinking plenty of non-alcoholic, non-caffeinated fluids

Hypothermia in cold houses

Older people, babies and young children in cold houses are at particular risk of developing hypothermia. To avoid getting too cold, taking some of the following steps may help:[20]

  • Dressing warmly inside on cold days, such as wearing socks and slippers
  • Keeping warm when sleeping. If not warm in pajamas, then wearing underwear as well
  • Making sure to eat regularly, including foods with plenty of protein and fat when it is cold
  • Drinking non-alcoholic, non-caffeinated fluids regularly
  • Checking on elderly friends regularly
  • Trying to ensure the house is warmed to between 68 degrees and 70 degrees Fahrenheit (20 to 21 degrees Celsius).
  • Shutting off rooms that will not be used in the house; this tip also reduces heating bills


Q: Hypothermia vs hyperthermia: what is the difference?
A: Hypothermia is when the body starts losing heat at a faster rate than it can produce more, whereas hyperthermia is when the body absorbs more heat than it can handle. It is an umbrella term that includes several conditions including heat cramps and heat stroke.[21] Malignant hyperthermia is a genetic condition that leads to a fast rise in body temperature.

Hyperthermia is often confused with fever. In fever, the body sets its core temperature at a higher than average level and then attempts to generate heat to stay at this temperature. In hyperthermia, the rise in body temperature is caused by an external factor, such as the sun or certain medications. Fever can have a variety of causes, including infection and genetically inherited conditions.[22]

Q: How long can someone survive in cold water before death by hypothermia
A: Giving a standard answer to this question is impossible, as a number of factors determine how long a person is likely to survive. These include:[23]

  • Water temperature
  • Whether the person is wearing clothing
  • The person’s body fat percentage

Water at near freezing level can cause hypothermia in under 15 minutes. However, the condition usually only becomes a danger at most sea and ocean temperatures after half an hour.

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