About hypothermia

You can develop hypothermia if you’re outside in cold conditions. Moving cold air, such as in windy conditions (known as the wind-chill factor), can cool your body quickly. If you're in cold water, you can lose body heat even faster.

You can also get hypothermia when you’re inside, for example if a room isn’t properly heated or if you aren't dressed in warm enough clothing. Hypothermia can particularly affect young children, adults over 65, and people who are frail or ill.

Your normal body temperature is 37ºC. If you have hypothermia, your body temperature drops to below 35ºC. There are different levels of hypothermia, based on how low your body temperature drops.

  • Mild hypothermia is when your body temperature is between 32 and 35ºC.
  • Moderate hypothermia is when your body temperature is between 28 and 32ºC.
  • Severe hypothermia is when your body temperature is less than 28ºC.

There are also different types of hypothermia, based on how quickly your body temperature falls.

  • Acute or immersion hypothermia is when you lose heat very quickly, for example by falling into cold water.
  • Subacute or exhaustion hypothermia is when your body is so tired it can no longer generate heat.
  • Chronic hypothermia is when your body temperature falls slowly over time.

Hypothermia can be life-threatening, so it’s important to seek urgent medical attention for treatment.

Symptoms of hypothermia

It can be difficult to know if you have hypothermia, but symptoms can include: 

  • shivering
  • a lack of energy
  • cold, pale, dry skin
  • not thinking clearly or being confused
  • being irritable or irrational
  • not remembering what has happened or who you are (amnesia)
  • finding it difficult to co-ordinate your body
  • finding it difficult to speak properly
  • feeling disorientated

As your body temperature falls, you may have a slow heart rate (pulse) or have slow, shallow breathing.

If you have, or a person you’re with has, any of these symptoms, it’s important to seek urgent medical attention.

Complications of hypothermia

If your body temperature falls to below 32ºC you can lose consciousness, which can lead to a coma and your heart may stop beating. You must call for emergency help if you’re with a person who has these symptoms. You, or the emergency services, may need to give the person with hypothermia cardiopulmonary resuscitation (CPR).

Causes of hypothermia

Hypothermia is caused by your body becoming too cold.

You’re more likely to get hypothermia if you:

  • are exposed to cold environments when you’re out walking or are in cold water
  • are immobile
  • are very slim or frail
  • are very tired – as you’re less able to generate heat and keep warm
  • aren’t aware of the cold because your ability to make decisions has been affected by alcohol or medicines
  • have hypothyroidism (underactive thyroid)
  • have an infection
  • have a chronic illness (the term ‘chronic’ refers to how long a person has it, not to how serious a condition is), such as diabetes

Diagnosis of hypothermia

If you have, or a person you’re with has, symptoms of hypothermia you should seek urgent medical attention. You may not have time to wait for a diagnosis; it’s important to start treating a person with hypothermia straight away.

In hospital, hypothermia may be diagnosed by measuring your core body temperature. If you’re admitted to hospital with hypothermia, you will have a series of tests to see how it has affected your body.

Treatment of hypothermia

If you develop the symptoms of hypothermia, it’s important to seek urgent medical attention.

If you’re with a person who has the symptoms of hypothermia, you should ask another person (if there is someone who is able) to call for emergency help. As a general guide, you should then try to:

  • protect the person from the elements and either provide or seek shelter
  • give the person warm but not hot drinks (only if he or she can hold and drink unaided) and high-energy foods such as chocolate
  • keep track of how the person is responding to being warmed by checking his or her breathing or pulse – this should increase as body temperature rises

There are a number of things you shouldn’t do if you’re with someone who has hypothermia. For example, you shouldn’t:

  • leave the person (unless there is no alternative)
  • give the person alcohol as this can make hypothermia worse – alcohol dilates the blood vessels near the skin, which has a cooling effect
  • rub the person’s skin as this increases heat loss

Warming a person with hypothermia outdoors 

If you’re outdoors with a person who has hypothermia, you should try to: 

  • warm him or her gradually as this will help ensure the person won’t be shocked by a sudden increase in temperature
  • seek shelter, remove any wet clothing, dry him or her and replace the clothes with dry garments to wear or cover them in dry blankets – and if possible use a space (thermal) blanket
  • cover his or her head
  • use your body heat to warm him or her by hugging the person, but only if you're not at risk of getting cold too
  • put together a layer of materials underneath him or her as protection from the ground, such as dry leaves, newspapers or branches

Warming a person with hypothermia indoors 

If you’re indoors with a person who has hypothermia, you should try to: 

  • put him or her in bed and covered with blankets
  • warm him or her in a water bath (for mild hypothermia) – the water should be warm but not hot, ie about 40ºC (if you can measure it with a thermometer)

Remember that direct heat, such as heat pads or hot water bottles, may cause burns so don't use them.

Animation - how CPR is carried out

If a person with hypothermia is unconscious and isn't breathing normally, you will need to do CPR. It’s also important to call for emergency help.         

Hospital treatment

If you need to have hospital treatment, you will be given warm fluids intravenously (through a drip inserted into a vein in your hand or arm). This helps to warm up your body internally. You may also be given a special air blanket that blows warm air onto your body.

Prevention of hypothermia

When you’re in cold conditions, make sure you wear appropriate cold weather clothing and take a survival bag, which should include a space blanket. Don’t drink alcohol if you anticipate being exposed to the cold.

Could hypothermia be mistaken for something else?


Yes. Sometimes the symptoms of hypothermia can be mistaken for other conditions.


Sometimes, hypothermia may be hiding the symptoms of a stroke, heart attack or hypothyroidism (an underactive thyroid), particularly in people over 65. Hypothermia can develop after a stroke, especially if you're less mobile or unable to adjust yourself or your surroundings to stay warm. There may be other causes, such as drinking too much alcohol, an infection or certain medicines, which can mask the original cause. 

If you think someone may have hypothermia, you should call for emergency help.

Is it true that you lose a third of your heat through your head?


You do lose some heat through your head, but it’s unlikely to be a third of all the heat that you lose from your body. If you cover your head, it can help to keep you warm.


You lose heat if your head isn't covered, but it's only thought to be about one tenth of your body heat.

Heat is lost if the air or water around you is cooler than your own temperature. You lose heat if you're sitting on a cold floor for example, which you will warm with your body heat, thus removing heat from you. Wind can be cooling because it takes away the warmth that immediately surrounds your body. Heat is also lost because of evaporation (the loss of water) from the surface of your skin through perspiration (sweating).

Your head isn't well insulated with layers of fat like other parts of your body. The blood vessels are close to the surface of your skin and this is how you lose heat. Babies have much larger heads in comparison to their body, so covering their head may be particularly important to keep them warmth.

Although it’s important to keep your head warm in cold conditions, you should also cover up the rest of your body to prevent hypothermia.

Why should I not rub a person's skin to warm up him or her?


If a person has hypothermia, rubbing his or her skin increases heat lost from their body.


Rubbing the skin causes the blood vessels to rise to the surface of the skin. The closer the vessels are to the surface of the skin, the more heat is lost because the warm blood comes into contact with the cooler temperature outside the body. This means the core body temperature decreases.

Insulating the person with warm blankets will help to decrease how close the blood vessels are to the outside temperature, and raise their core temperature.