Human SkillsStaying Warm, Staying Cool
Recognise hypothermia and heat illness early and act on them
6 minIntermediateUpdated
- Dress in layers that manage sweat, warmth and wind
- Spot the early signs of hypothermia and heat exhaustion
- Give correct first response while calling for help
The layering system
Your body is the heater; clothing is the insulation and the wind shield. Use three layers. A base layer of synthetic fabric or merino wool pulls sweat off your skin; cotton holds water and chills you, so leave cotton at home. A mid layer of fleece or a light insulated jacket traps warm air. An outer shell blocks wind and rain. The trick is to change layers before you need to: take a layer off when you start to feel warm on a climb, so you never soak your clothes with sweat, and put one on the moment you stop moving. Hat, gloves and a neck gaiter add warmth for almost no weight.
Hypothermia: the umbles
Hypothermia is a core body temperature below 35 degrees Celsius, and it starts long before freezing weather; wind and wet at 10 degrees are enough. Early signs are the umbles: the person mumbles, stumbles, fumbles with zips and grumbles about things they would normally ignore. Shivering is intense at first. As it worsens, shivering stops, speech slurs, and the person becomes confused, drowsy and may insist they are fine. A hypothermic person cannot judge their own state, so watch your companions and act on what you see. Treat early shivering as a warning to fix the situation immediately, not a reason to push on.
Warming someone safely
Get the person out of wind and wet. Replace wet clothes with dry ones, or wrap them in a sleeping bag with a foil blanket outside it, insulated from the ground. Cover the head. If they are alert and can swallow, give warm sweet drinks and food; the body needs fuel to make heat. Put warm water bottles wrapped in cloth against the chest, armpits and groin. Do not rub the limbs, give alcohol, or put them in a hot bath, because these can push cold blood to the heart. If shivering has stopped, they are confused or drowsy, or they are not improving, call local emergency services now and handle them gently while you wait.
Heat exhaustion and heat stroke
Heat exhaustion comes from losing water and salt in the heat. The person is sweating heavily, pale, dizzy, nauseous, has a headache and cramps, and a fast weak pulse. Move them to shade, lie them down with legs raised, loosen clothing, cool them with wet cloths and fanning, and give water or a sports drink in small sips. They should improve within 30 minutes. Heat stroke is the emergency: body temperature above 40 degrees, hot skin that may be dry or wet, confusion, slurred speech, seizures or collapse. Call emergency services immediately and cool the person aggressively with water and fanning while you wait. Never give drinks to someone who is confused.
Staying cool
In heat, plan activity for early morning and evening and rest in shade between 11 and 17. Wear loose, light-coloured clothing and a wide-brimmed hat; covered skin stays cooler than bare skin in strong sun. Drink before you are thirsty, aiming for about half a litre an hour when active, and eat salty snacks to replace what sweat removes. Wet your hat and neck whenever there is spare water. Keep an eye on urine colour: pale yellow is right, dark means drink more. Check on children, older people and anyone unwell, because they overheat faster and notice later. Never leave anyone, or a pet, in a parked car.
Check yourself
Cotton soaks up sweat and rain and holds it against your skin, pulling heat away for hours.
Shivering stopping with confusion is a sign of moderate to severe hypothermia. Call emergency services and insulate them.
Rubbing limbs pushes cold blood back to the heart. Warm the core gently and insulate.
Confusion, collapse or a temperature above 40 degrees Celsius means heat stroke, a medical emergency needing immediate cooling and a call to emergency services.
Try it for real: Audit your layers and your heat plan
- Lay out your outdoor clothes and sort them into base, mid and shell layers, removing any cotton
- Add a hat, gloves and a foil blanket to your walking bag
- On your next warm-day walk, drink half a litre an hour and check urine colour afterwards
- Teach one family member the umbles signs of hypothermia
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Written and checked by the Human Skills team against the sources below. How we check our content
- Red Cross First Aid
- WHO Heat and Health guidance
- Wilderness Medical Society Practice Guidelines
