Why hypothermia catches hill walkers out

Hypothermia is not just a winter problem. Most cases in the UK hills happen in spring, autumn and even summer, when a mild day turns wet and windy and a walker stops moving. Wind and rain strip heat away far faster than cold air alone, and a sweaty base layer is as dangerous as no layer at all. The real danger is how gradually it develops. Someone can slip from "a bit cold" to genuinely hypothermic in half an hour, and they are usually the last person to notice. That is why we look after each other rather than relying on self-assessment.

The early signs: shivering, fumbling and the umbles

Mild hypothermia is the stage where you can still fix things easily, so this is the stage to learn by heart. The classic markers are persistent shivering that continues even when the casualty is out of the wind, cold pale or greyish skin, and blue lips or fingertips. Watch for clumsiness too: a walker who suddenly cannot work a zip, fumble a map case, open a rucksack or get a glove on is showing a real warning sign. So is slurred speech, uncharacteristic grumbling or a flat, withdrawn mood.

Instructors often use the umbles to remember it:

• Grumbles — unusual irritability or complaining.
• Mumbles — slurred or muddled speech.
• Fumbles — dropping things, poor coordination with hands.
• Stumbles — tripping, staggering, or a sudden loss of walking rhythm.

A simple test is the talk test: if they cannot hold a normal conversation while walking, or cannot answer basic questions such as the day of the week, where they are, or counting backwards from twenty, treat it as significant. Cold hands and feet, hunger, thirst and exhaustion all make it worse, so stop early and check each other at every break.

When shivering stops

Shivering is uncomfortable but it is your friend: it means the body is still fighting to generate heat. If shivering stops while the casualty is still cold, still wet and still exposed, that is a serious deterioration. They may become drowsy, confused, unusually quiet, or reluctant to move. Breathing may become slow and shallow, the pulse slow and weak, and muscles may feel stiff. They may deny anything is wrong. At this point, do not make them walk, and handle them gently. A cold heart is easily irritated by rough movement, so avoid jolting them around.

Shelter first: stop the heat loss

Before you warm anyone, stop them losing more heat. Get them out of the wind and rain as fast as possible — behind a boulder, in a hollow, into a bothy, tent or group shelter. Insulate them from the ground with a sleeping mat, rucksack or dry bracken, because sitting on cold rock drains heat quickly. Remove wet clothing and replace it with dry layers, then add a windproof shell, hat, gloves and a sleeping bag or blanket. Cover the head and neck. If you have a group, huddle together: shared body heat is remarkably effective. Keep the casualty horizontal if they are moderate or worse, and keep them still.

Warm slowly and steadily

Rewarming should be gradual and focused on the core. If the casualty is fully conscious and can swallow safely, give a warm, sweet drink — not alcohol, and not a strong coffee. Sugar helps, and warm fluids help from the inside. Do not rub their limbs briskly or massage cold arms and legs; this pushes cold blood back towards the heart and can cause a dangerous further drop in core temperature, known as afterdrop. Instead, apply gentle warmth to the torso, armpits, groin and neck using your own body heat, a warm (not scalding) water bottle wrapped in cloth, or chemical heat packs placed on the torso over a layer of clothing. Skin-to-skin contact inside a sleeping bag works well. Never put a hypothermic casualty in a hot bath or shower.

Getting help and preventing a repeat

Mild cases who warm up fully, are dry and can eat and drink may be able to walk out slowly with their load shared. Moderate and severe cases should not walk: keep them still, keep warming them, and call for help. Dial 999 and ask for the police, then mountain rescue, giving a clear grid reference along with a description of the location and the casualty's condition. Keep monitoring breathing and responsiveness while you wait.

Prevention is simply good hill craft: eat and drink before you feel cold, wear wicking layers rather than cotton, carry a spare dry layer, wear a hat and gloves, check the mountain forecast, keep the group together, and be willing to turn back early. Look after each other on the hill, and hypothermia is something you will rarely have to treat.