Hypothermia is when a person's normal body temperature of around 37°C (98.6°F) drops below 35°C (95°F).
It is usually caused by being in a cold environment. It can be triggered by a combination of things, including prolonged exposure to cold (such as staying outdoors in cold conditions or in a poorly heated room for a long time), rain, wind, sweat, inactivity or being in cold water.
Types of hypothermia
There are different types of hypothermia, which depend on how quickly the body loses heat.
Acute or immersion hypothermia occurs when a person loses heat very rapidly, for example by falling into cold water.
Exhaustion hypothermia occurs when a person's body is so tired it can no longer generate heat.
Chronic hypothermia is when heat loss occurs slowly over time. This is common in elderly people living in a poorly heated house, or in people sleeping rough.
When your body gets cold, the normal response is to warm up by becoming more active, putting on more layers or moving indoors. But if exposure to the cold continues, your body's automatic defence system will try to prevent any further heat loss by:
shivering (which keeps the major organs at normal temperature),
restricting blood flow to the skin, and
releasing hormones to generate heat.
After prolonged exposure to the cold, these responses are not enough to maintain body temperature, as they also drain energy.
When the body's energy is exhausted, it slowly starts to shut down. Shivering stops and your heartbeat begins to slow. This life-threatening stage can develop very quickly, so it is vital that hypothermia is treated as a medical emergency.
Each year in the UK, hypothermia is the main contributing factor to the deaths of more than 400 people over the age of 65.
Elderly people and those who are ill and unable to move around easily are especially vulnerable to hypothermia. This can be due to poorly heated accommodation, not eating enough or not being active enough to generate energy.
If the weather is cold, dress appropriately before you go outside. Even if the rest of the body is covered up, significant amounts of body heat can be lost through the head, so wear a warm hat.
Layers of clothing trap air, which helps to keep you warm. Tightly woven, waterproof clothes are best when outside
Drink plenty of fluids and hot drinks (not alcohol) and eat regular, balanced meals to give you energy
Keep active when it is cold, but not to the point where you are sweating. If you exercise outdoors in the winter and get sweaty from this, make sure you dry off and put on warm clothes immediately after.
Keep dry and change out of wet clothes as soon as possible. Wet clothes lose about 90% of their insulating power.
Cut down on alcohol, caffeine and nicotine as all three aggravate heat loss.
Keep your house warm during cold weather. If you are concerned about heating costs, you could try just keeping one room in the house warm. Keeping windows and doors closed also helps to trap heat
The symptoms of hypothermia depend on how cold the environment is and how long you are exposed for.
Severe hypothermia needs urgent medical treatment in hospital. Shivering is a good guide to how severe the condition is. If the person can stop shivering on their own, the hypothermia is mild, but if they cannot stop shivering, it is moderate to severe
In mild cases, symptoms include:
low energy, or
cold, pale skin
The symptoms of moderate hypothermia include:
violent, uncontrollable shivering,
being unable to think or pay attention,
confusion (some people don't realise they are affected),
loss of judgment and reasoning,
difficulty moving around or stumbling (weakness),
fumbling hands and loss of coordination,
listlessness and indifference, or
slow, shallow breathing and a weak pulse.
The symptoms of severe hypothermia include:
loss of control of hands, feet, and limbs,
uncontrollable shivering that suddenly stops,
shallow or no breathing,
weak, irregular or no pulse,
stiff muscles, and
As hypothermia can be a life-threatening condition, seek medical attention as soon as possible.
Hypothermia is treated by preventing further heat being lost and by gently warming the patient.
Things to do for hypothermia
Move the person indoors, or somewhere warm, as soon as possible.
Once sheltered, gently remove any wet clothing and dry the person.
Wrap them in blankets, towels, coats (whatever you have), protecting the head and torso first.
Your own body heat can help someone with hypothermia. Hug them gently.
Increase activity if possible, but not to the point where sweating occurs, as that cools the skin down again.
If possible, give the person warm drinks (but not alcohol) or high energy foods, such as chocolate, to help warm them up.
Once body temperature has increased, keep the person warm and dry.
It is important to handle anyone that has hypothermia very gently and carefully.
Things you should NOT do
Don't warm up an elderly person using a bath, as this may send cold blood from the body's surfaces to the heart or brain too suddenly, causing a stroke or heart attack.
Don't apply direct heat (hot water or a heating pad, for example) to the arms and legs, as this forces cold blood back to the major organs, making the condition worse.
Don't give the person alcohol to drink, as this will decrease the body's ability to retain heat.
Don't rub or massage the person's skin, as this can cause the blood vessels to widen and decrease the body's ability to retain heat. In severe cases of hypothermia there is also a risk of heart attack.
Severe hypothermia needs urgent medical treatment in hospital. Shivering is a good guide to how severe the hypothermia is. If the person can stop shivering of their own accord, hypothermia is mild, but if they cannot stop shivering, it is moderate to severe.
Visit your GP regularly to manage any illnesses effectively. If you are taking regular medication, ask whether it affects your body's ability to regulate your temperature.