Hypothermia occurs 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 persons 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.
Who is most at risk?
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 accomodation, not eating enough or not being active enough to generate energy.
People who spend a lot of time in extreme weather conditions, such as climbers and skiers, are at a higher risk, especially if they are not wearing suitable clothing.
Babies are also more prone to hypothermia because their body's ability to regulate its temperature is not fully developed. They lose heat quickly if left in a cold room for too long.
