Hypothermia

Hypothermia happens when a person's body temperature drops below 35°C (95°F).

Information written and reviewed by Certified Doctors.

Contents

Introduction

Hypothermia happens when a person's body temperature drops below 35°C (95°F). Normal body temperature is around 37°C (98.6°F).

Hypothermia can quickly become life threatening and should be treated as a medical emergency.

It's usually caused by being in a cold environment and can be triggered by a combination of things – such as being outdoors in cold conditions for a long time, living in a poorly heated house or falling into cold water.

Who's at risk?

People who are particularly at risk are those who are elderly or ill and are unable to move around easily to generate heat. During 2011-12, around 1,500 people seen in hospital were diagnosed with hypothermia, and more than 1,000 were over 60 years of age.

Babies are also more prone to developing hypothermia because their bodies' ability to regulate their temperature isn't fully developed.

However, it is not just babies and elderly people who develop hypothermia. Anyone who spends long periods outside during the winter without wearing appropriate warm clothing can also be at risk, particularly after drinking large amounts of alcohol.

For example, there have been several cases in recent years of young people developing hypothermia while making their way home drunk after a night out. They were lightly clothed and lost their way home, only to be discovered dead, or close to death, with severe hypothermia.

People who spend a considerable amount of time outside in cold weather conditions, such as climbers and skiers, are also at increased risk of getting hypothermia, particularly if they don't wear suitable clothing.

Read more about the causes of hypothermia.

Signs of hypothermia

The signs of hypothermia vary depending on how low a person’s temperature has dropped.

Initial symptoms include shivering, tiredness, fast breathing and cold or pale skin.

As the temperature drops, shivering becomes more violent (although this will stop completely if the hypothermia worsens further), the person is likely to become delirious, struggle to breathe or move and they may lose consciousness.

Babies with hypothermia may look healthy but their skin will feel cold. They may also be limp, unusually quiet and refuse to feed.

Read more about the symptoms of hypothermia.

When to get medical help

You should seek immediate medical help if you suspect someone has hypothermia.

If someone you know has been exposed to the cold and they are distressed, confused, have slow, shallow breathing or they're unconscious, they may have severe hypothermia. In this case, immediately request an ambulance.

Helping someone with hypothermia

While waiting for medical help, it is important to try to prevent further heat loss and gently warm the person. You should:

  • Move the person indoors or somewhere warm as soon as possible.
  • Once they are somewhere warm, carefully remove any wet clothing and dry the person.
  • Wrap them in blankets, towels or coats.

If the person is unconscious, not breathing and you can't detect a pulse in their neck after 60 seconds, cardio-pulmonary resuscitation (CPR) should be given if you know how to do it. Once CPR is started, it should be continued without any breaks until medical assistance arrives.

Once in hospital, advanced medical treatments – such as removing blood from the body, heating it, and returning it to the body – can be used to warm the person up.

Read more about treating hypothermia.

Preventing hypothermia

There are several things you can do to prevent hypothermia. Simple measures can help, such as wearing appropriate warm clothing in cold weather and ensuring that children are well wrapped up when they go outside.

Whenever possible, keep an eye on elderly or ill neighbours and relatives to ensure that their home is warm during cold weather.

Read more about preventing hypothermia.

Symptoms

The symptoms of hypothermia can vary depending on how low your body temperature has become.

The early symptoms of hypothermia are often recognised by a parent or carer. This is because hypothermia can cause confusion, poor judgement and changes in behaviour, which means the affected person may not realise that they have it.

Mild hypothermia

If someone has mild hypothermia (generally with a body temperature of 32-35˚C), the symptoms aren't always obvious but they can include:

  • constant shivering
  • tiredness
  • low energy
  • cold or pale skin
  • fast breathing (hyperventilation)

Moderate hypothermia

Moderate cases of hypothermia (generally with a body temperature of 28-32˚C) can include symptoms such as:

  • being unable to think or pay attention
  • confusion
  • loss of judgement and reasoning (someone with hypothermia may decide to remove clothing despite being very cold)
  • difficulty moving around
  • loss of co-ordination
  • drowsiness
  • slurred speech
  • slow, shallow breathing (hypoventilation)

People with a body temperature of 32˚C or lower will usually stop shivering completely. This is a sign that their condition is deteriorating and emergency medical help is required.

Severe hypothermia

The symptoms of severe hypothermia (a body temperature of below 28˚C) can include:

  • unconsciousness
  • shallow or no breathing
  • weak, irregular or no pulse
  • dilated pupils

Someone with severe hypothermia may appear to be dead. However, under these circumstances the individual must be taken to hospital to determine whether they have died, or if they are in a state of severe hypothermia. Medical treatment can still be used to resuscitate people with severe hypothermia, although it is often fatal.

Hypothermia in babies

Babies with hypothermia may look healthy but their skin will feel cold. They may also be limp, unusually quiet and refuse to feed.

When to seek medical attention

If you suspect hypothermia, seek medical attention as soon as possible.

If you suspect someone has severe hypothermia, immediately request an ambulance.

Causes

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

There are different types of hypothermia depending on how quickly the body loses heat. The three types are described by doctors as:

  • acute or immersion hypothermia, which happens when a person loses heat very rapidly – for example, after falling into cold water
  • exhaustion hypothermia – this happens when a person’s body is so tired it can no longer generate heat
  • chronic hypothermia – 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 is a cool wind), the water evaporates from your skin and lowers your body temperature.

Who's at risk?

Some people are at an increased risk of getting hypothermia because they're vulnerable to cold environments or they're unable to keep warm. These include:

  • Babies can lose heat quickly if they're left in a cold room because they can't regulate their body temperature as well as older children and adults. Newborn babies in particular are at risk for the first 12 hours of their life.
  • Older people, particularly if they're not very active, do not eat enough, have other illnesses or take medication that can interfere with the body's ability to regulate temperature.
  • Homeless people who are unable to find shelter.
  • Heavy drug and/or alcohol users – these substances affect the body's ability to retain heat. The blood vessels stay widened (dilated), allowing heat to escape. Someone who is under the influence of drugs or alcohol may also not realise they have hypothermia.
  • People with a condition that affects their memory, such as Alzheimer's disease, may not be able to recognise the symptoms of hypothermia or recognise when they're cold.
  • People with certain health conditions, such as heart problems, severe arthritis or someone who has 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, which can interfere with the body's ability to regulate temperature.
  • Someone who has fallen into cold water, which can cause the body's core temperature to fall very quickly.
  • People who spend long periods in cold weather conditions, such as climbers, walkers and skiers.
  • Someone who has had a severe injury, particularly a head injury.

Read more about preventing hypothermia.

Perioperative hypothermia

It is 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 stay in hospital. They will monitor your temperature and may use a special blanket into which warm air is blown 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.

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.

This group of people includes those who have suffered a cardiac arrest due to a heart attack outside of hospital, but who have been successfully resuscitated and are in an intensive care unit.

Treatment

Hypothermia is treated by preventing further heat being lost and by gently warming the patient.

You should seek immediate medical attention if you suspect someone has hypothermia, as it can be life threatening. Read more about the symptoms of hypothermia.

Treating hypothermia at home

If you're treating someone with mild hypothermia at home, or waiting for medical treatment to arrive, the following advice will help prevent further heat loss.

  • Move the person indoors or somewhere warm as soon as possible.
  • Once the person is in a warm environment, carefully remove any wet clothing and dry the person.
  • Wrap them in blankets, towels, coats (whatever you have available), protecting their head and torso first.
  • Your own body heat can help someone with hypothermia. Gently hugging them can help warm them up.
  • Encourage the person to shiver if they're capable of doing so.
  • If possible, give the person warm drinks (not alcohol) or high-energy foods, such as chocolate, to help warm them up. However, it's important to only do this if they can swallow normally (ask them to give a cough to see if they can swallow).
  • Once the person’s body temperature has increased, keep them warm and dry.

It's important to handle anyone with hypothermia gently and carefully.

Things to avoid

There are certain things you should not do when helping someone with hypothermia because it may make the condition worse:

  • Do not put the cold person into a hot bath
  • Do not massage their limbs
  • Do not use heating pads and lamps
  • Do not give them alcohol to drink

Trying to warm someone up yourself with hot water, massages, heat pads and heat lamps can cause the blood vessels in the arms and legs to open up (dilate) too quickly. If this happens, it can lead to a fall in blood pressure to the vital organs such as the brain, heart, lungs and kidneys, potentially resulting in cardiac arrest and death.

Severe hypothermia

If someone you know has been exposed to the cold and they're distressed or confused, they have slow, shallow breathing or they're unconscious, they may have severe hypothermia. Their skin may look healthy but feel cold. Babies may also be limp, unusually quiet and refuse to feed.

Cases of severe hypothermia require urgent medical treatment in hospital. You should call 999 to request an ambulance if you suspect someone you know has severe hypothermia.

As the body temperature drops, shivering will stop completely. The heart rate will slow and a person will gradually lose consciousness. They won't appear to have a pulse or be breathing. If you know how to do it, cardio-pulmonary resuscitation (CPR) should be given while you wait for help to arrive.

Medical treatment

If someone is admitted to hospital with severe hypothermia, advanced medical treatment can be used to warm them up.

This can be done by temporarily withdrawing blood from the body, warming it, and then returning it to the body. These techniques are cardio-pulmonary bypass (sometimes called heart-lung bypass) and extra corporeal membranous oxygenation (ECMO).

However, techniques such as this are usually only available in major hospitals that have specialist emergency services or units that regularly perform heart surgery.

A person with severe hypothermia often stands a better chance of surviving if they're taken directly by ambulance to one of these hospitals, even if it means bypassing a smaller hospital along the way.

Prevention

There are simple measures you can take to prevent you, your child or elderly relatives getting hypothermia.

Staying warm inside

Keep an eye on elderly or ill neighbours and relatives to ensure they are keeping their house warm during cold weather. Keeping windows and internal doors closed will also help trap heat.

Use a room thermometer to ensure your house is at the right temperature. It is recommended to keep your main living room at 18-21°C (64-70°F) and other rooms at a minimum 16°C (61°F).

If you have a baby, keep the room they sleep in at 16-20°C (61-68°F).

A healthy diet with plenty of fluids, warm drinks and regular meals can help provide energy so your body can generate heat. Avoiding alcohol, caffeine and smoking can also help as they all increase the rate at which the body loses heat.

If you're ill, visit your local pharmacy or doctor to ensure you're treated promptly and effectively. If you're taking regular medication, ask whether it affects your body's ability to regulate temperature.

Staying warm outside

Wear appropriate warm clothing in cold weather and make sure your children are well wrapped up when outdoors. A significant amount of body heat can be lost through the head, even if the rest of the body is covered up, so you and your children should wear a warm hat.

Multiple thin layers of clothing trap air, which keeps you warm more effectively than one thick layer. Waterproof and windproof clothing gives the best protection outdoors in the sort of weather conditions found in the UK.

Eating and drinking regularly (but not alcohol and caffeine) and having warm drinks can also help keep you warm outside.

Keep active when it's cold, but not to the point where you are sweating. If you exercise outdoors during the winter and you sweat after exercising, make sure you dry off and put on warm clothes immediately afterwards. Wet clothes lose around 90% of their insulating power.

Content supplied by NHS Choices