Causes of hypothermia 

Hypothermia is caused by getting too cold, as the body loses more heat than it can generate and body temperature drops below 35C (95F).

There are different types of hypothermia, depending on how quickly the body loses heat:

  • acute or immersion hypothermia – this happens when a person loses heat very rapidly; for example, after falling into cold water
  • exhaustion hypothermia – this happens when the body is so tired it can no longer generate heat
  • chronic hypothermia – where heat is lost slowly over time; this is common in elderly people who live in poorly heated accommodation or in people sleeping rough

Hypothermia is most common in cold environments. You're more at risk if you don't wear enough layers to keep warm or you don't cover your head (a large amount of body heat is lost through your head).

It's also possible to get hypothermia in mild weather. For example, if you're soaked in the rain and don't dry off properly soon afterwards – particularly if there's a cool wind – the water evaporates from your skin and lowers your body temperature.

Who's at risk?

Certain groups of people are at an increased risk of developing hypothermia because they're vulnerable to cold environments or they're unable to keep warm.

  • babies – can lose heat quickly if they're left in a cold room as they can't regulate their body temperature as well as older children and adults; newborn babies are particularly at risk for the first 12 hours of their life
  • older people – particularly if they're not very active, don't eat enough, have other illnesses, or take medication that can interfere with the body's ability to regulate temperature
  • homeless people – if they are unable to find shelter
  • heavy alcohol or drugs – this is because these substances affect the body's ability to retain heat: the blood vessels stay widened, allowing heat to escape
  • people with a condition that affects their memory – people with conditions such as Alzheimer's disease may not be able to recognise if they're cold or if they have the symptoms of hypothermia
  • people with certain health conditions – such as heart problems, severe arthritis, or someone who's had a stroke; these conditions can change the body's ability to respond to temperature changes, for example, by affecting the fingers and toes (where you may first feel cold)
  • people taking sedatives – these can interfere with the body's ability to regulate temperature
  • someone who's fallen into cold water – this can cause the body's core temperature to decrease very quickly
  • people who spend long periods in cold weather conditions – such as climbers, walkers and skiers
  • someone who's had a severe injury – particularly a head injury

Read more about preventing hypothermia.

Perioperative hypothermia

It's also sometimes possible for hypothermia to occur during a stay in hospital, particularly before, during and after an operation. This is known as perioperative hypothermia.

Hospital staff will try to ensure you stay warm during your hospital stay. They'll monitor your temperature and may use a special blanket that has warm air is blown into it to help stop you getting too cold. This is called forced air warming.

You should tell staff if you feel cold at any time during your stay in hospital.

Read the National Institute for Health and Care Excellence (NICE) guidelines for more information about the management of inadvertent perioperative hypothermia in adults (PDF, 174kb).

Therapeutic hypothermia

In some cases, medical professionals may deliberately make someone develop hypothermia as a treatment. This is known as therapeutic hypothermia.

There's evidence to suggest that, in some circumstances, inducing a state of hypothermia in the body can reduce the risk of death and increase the chances of a good recovery.

People who may receive this type of treatment include those who've had a cardiac arrest caused by a heart attack outside a hospital, but who've been successfully resuscitated and are in an intensive care unit.

Page last reviewed: 20/04/2015

Next review due: 20/04/2017