Hypothermia Symptoms & Treatment Outdoors: Signs, First Aid, Prevention

Before you read on

What is hypothermia – and why 5–10 °C is the classic weather

Your body works within a narrow band around 37 °C. In the cold it defends that temperature in two ways: it narrows the blood vessels in skin, hands and feet to keep warm blood in the core, and it makes extra heat by shivering. Hypothermia begins when those defences are no longer enough and the core temperature drops below about 35 °C. From there, muscles, brain and heart work progressively worse – which is why the person affected is usually the last to notice.

Most outdoor cases are not dramatic blizzard stories. They happen on ordinary cool days to people who are wet, tired and under-fuelled: a long walk in drizzle at 8 °C, a windy ridge, a capsized canoe in spring, an evening at camp in damp clothes. Wet clothing and wind strip heat far faster than still, dry cold. At 5 °C, a 20 km/h wind already feels like about 1 °C; the wind chill calculator shows the effect for your conditions, and reading the weather tells you when it is coming.

The five ways the body loses heat

Read the table the other way round and you have the whole treatment: get out of the wind, get off the ground, get dry, cover the head, and add insulation. Everything else in this article is detail.

Who is at risk of hypothermia when hiking and camping?

Anyone can become hypothermic, but some situations and people cool much faster. The more points on this list apply, the earlier you should stop and add warmth.

The typical chain is easy to recognise in hindsight: a late start, a longer route than planned, no proper lunch because it was raining, a soaked base layer under a shell, and then a stop on a windy col. Each link is harmless alone. Good planning breaks the chain early – a realistic route (see the hiking time calculator and the daylight calculator), a turnaround time, and the discipline to stop before everybody is cold.

An injured person deserves special attention. Someone who has twisted an ankle and sits on wet ground cools quickly even in mild weather, because they have stopped making heat by moving and are losing it into the ground. Insulating a casualty is part of first aid for every injury, not only for cold.

Hypothermia symptoms: how to recognise the signs

You will not have a thermometer that measures core temperature in the woods, and you do not need one. First aiders, mountain rescue teams and wilderness medicine guidelines judge hypothermia by what they see: is the person shivering, how alert are they, how do they move and speak?

The "umbles" – signs of hypothermia when hiking

The early signs are easy to remember as the "umbles":

• Stumbles – tripping, wandering off line, slow and unsteady walking.
• Mumbles – slurred, slow or short answers.
• Fumbles – cannot do up a zip, drops things, struggles with laces or a lighter.
• Grumbles – irritable, apathetic, withdrawn, "I'm fine, leave me alone".

Together with shivering and cold, pale skin, they mean the body is struggling. The person often denies it – judgement is one of the first things to go. So the rule in a group is: if you see the umbles in someone else, you decide, not they.

Shivering present, shivering stopped

Shivering is the most useful single sign. Strong shivering in someone who is awake and coherent means the body still has fuel and control: with shelter, dry insulation and food it can usually rewarm itself. Shivering that fades in a person who is still cold, still wet and getting quieter is the opposite of good news. It means the energy is running out and the core is cooling further. "They have stopped shivering, so they are better" is one of the most dangerous misreadings in the outdoors. Someone who is genuinely warming up becomes more talkative, more coordinated and pinker – not sleepier.

Buddy checks: an early-warning routine

In cold, wet weather build a short check into every stop. It takes a minute and catches the problem at the stage where a flask of tea still solves it.

On your own, nobody runs the check for you. Set yourself fixed triggers instead: if you cannot work a zip or your lighter, if you have stumbled twice on easy ground, or if you notice you no longer care about being cold, you stop and deal with it. A solo first night out in the cold season should always be close to home or the car.

How to treat hypothermia outdoors while it is still mild

A shivering, alert person can be rewarmed in the field – if you stop the heat loss completely. The order matters: shelter first, then dry, then insulation, then fuel. Changing clothes on an exposed ridge in the rain costs more heat than it saves.

Food, drink and gentle movement

Shivering burns a lot of energy, so a mildly hypothermic person needs fuel. The standard advice from the NHS and Red Cross societies is the same: give a warm, non-alcoholic, sweet drink and sugary food such as chocolate – but only to someone who is fully awake and able to swallow. The sugar matters more than the temperature of the drink; lukewarm sweet tea is fine, and it must not be scalding. A stove and a mug are part of your emergency kit in the cold season – see camp stoves and boiling water.

What about moving to warm up? Wilderness medicine guidance is cautious. Let the person rest, sheltered and insulated, for about half an hour first and watch them. If they are clearly improving – shivering less because they are warmer, talking normally, hands working – gentle activity such as walking slowly is reasonable and helps make heat. If they are not improving, or were ever confused or drowsy, they are not walked out: you insulate, call for help and wait.

If any of these points is missing after a proper rest, treat it as moderate hypothermia: wrap, call, wait. And after even a mild episode, the trip plan changes – shorten the route, head for a hut, the car or a sheltered camp with a fire (lighting a fire in wet weather is worth practising for exactly this day; in snow and hard frost, see fire in snow and cold).

The hypothermia wrap ("burrito") step by step

A hypothermia wrap is the outdoor version of putting someone to bed: insulation all round, a layer that keeps moisture in and a shell that keeps wind and rain out. Mountain rescue teams and wilderness first aid courses teach it because a cold person in a sleeping bag alone still loses heat into the ground and through wet clothing. You can build it from what a normal camping kit contains.

Wet clothing: change or leave on?

For a mildly hypothermic person in shelter, the answer is simple: wet off, dry on. For a moderately or severely chilled person, undressing means moving them a lot and exposing them to wind. First aid sources put it this way: remove wet clothing if you are sheltered and have dry clothing or blankets to replace it. If not, leave it on, wrap the vapour barrier directly over the wet layers and put the insulation outside it. If clothing has to come off a very cold person, cut it away rather than pulling limbs through sleeves.

Heat sources: warm, wrapped, on the torso

Insulation does most of the work. Added heat is a bonus and has to be used carefully, because cold skin burns easily and does not feel it. Advice for lay first aiders (for example from the NHS) is not to use hot baths, hot-water bottles or heat lamps. Mountain rescue and wilderness medicine guidelines do use heat packs and warm bottles, with firm rules: warm rather than hot, always wrapped in cloth and over clothing, placed on the chest, in the armpits or on the upper back – never on bare skin and never on arms or legs – and checked regularly. If you are unsure, leave them out and concentrate on a dry, windproof, well-insulated wrap.

Moderate and severe hypothermia: what to do until help arrives

Once a person is confused, drowsy, no longer shivering or cannot walk, you are no longer rewarming them yourself. Your job is to stop further cooling, avoid doing harm and get professional help moving. Call early – rescue in bad weather takes time.

Why so gentle? Afterdrop and rescue collapse, simply explained

In a deeply chilled person the blood in arms and legs is much colder than the blood around the heart. Rough handling, standing them up, rubbing the limbs or warming the limbs first can send that cold blood back to the core: the core temperature drops further even though the person is now "being rescued". This is called afterdrop. At the same time the cold heart is irritable and blood pressure is fragile, so sudden movement or sitting upright can trigger a dangerous heart rhythm or collapse – rescue services speak of rescue collapse. You do not need to remember the physiology. Remember the behaviour: flat, slow, gentle, warm the trunk and not the limbs.

No signs of life?

A severely hypothermic person can look dead: cold, grey, stiff, with breathing and pulse so slow and weak that they are hard to find. Cold also protects the brain, and people have recovered after long periods in this state. That is why the guidance of resuscitation councils and public health bodies is clear: do not give up on a cold casualty. Look, listen and feel for breathing for longer than you normally would – rescuer guidelines allow up to a minute. If there are no signs of life and you are trained, start CPR, tell the emergency dispatcher and continue until professionals take over. Whether and how long resuscitation continues is a decision for the rescue service and the hospital, not for first aiders on the hill.

When to call for help – and what to tell the dispatcher

In the European Union the emergency number is 112; in the UK dial 999 or 112 (for the hills, ask for the police and then mountain rescue); in the US and Canada 911. If you are unsure whether it is "bad enough", call anyway – dispatchers would rather advise early than search at night.

No signal? Try 112 anyway, move a short way to higher or more open ground if someone can do so safely, and use the whistle and light signals described in emergency and distress signals. If someone has to go for help, send two people if the group allows it, with the location written down – a result of good map and compass work – and leave the warmest, most capable person with the casualty.

Preventing hypothermia: stay dry, fed and ahead of the cold

Hypothermia is far easier to prevent than to treat. Prevention is not about toughness; it is a set of small habits that keep you dry, fuelled and honest about how the group is doing.

Layering and staying dry

Dress in layers that you actually adjust: a wicking base layer, an insulating mid layer and a wind- and waterproof shell. Wet cotton next to the skin is the classic mistake. The details are in our guide to bushcraft clothing and the layering system. Two rules do most of the work:

• Do not sweat. Start walking slightly cool, open zips and take a layer off before you overheat on the climb. Sweat-soaked clothing chills you at the next stop exactly like rain. On snow, see winter hiking in snow.
• Put the shell on before you are wet and the warm layer on the moment you stop – not after ten minutes of standing around.

Eating, drinking and pacing

Your body heats itself with food. Eat something every hour or so in cold, wet weather, even when stopping is unpleasant, and drink regularly – you lose water in cold air without feeling thirsty. Plan food you can eat with gloves on and without unpacking; trail meal planning, the food calculator and the water calculator help with the numbers. Walk at the pace of the slowest member, keep stops short and sheltered, and agree a turnaround time before you start.

Kit that prevents an emergency

The emergency blanket and bivvy bag are part of the first aid kit; the dry layer and flask belong on every cold-season bushcraft kit list. You can check the weight of the whole setup in the Kit Builder.

Camp routine in cold, wet weather

Choosing the spot is half the routine: avoid cold hollows and exposed crests, as explained in campsite selection and camp setup. A bivvy bag adds wind protection and a few degrees to any sleep system.

Sleeping warm

Many mild cases start at night, in a sleeping bag that is too thin on a pad that is too cold. A sleeping bag does not make heat; it only keeps what you bring into it. So eat before bed, go to bed warm, wear dry sleep clothes and a hat, and insulate properly from the ground – the pad's R-value matters as much as the bag's rating. The sleeping gear guide explains comfort ratings and pads, the sleep system calculator checks your setup against the forecast low, and the winter camping guide covers nights in frost. If you wake up shivering and cannot stop, do not wait for morning: eat, add every layer, do sit-ups in the bag, make a hot drink – and wake your companion.

Falling into cold water: the 1–10–1 principle

Cold water is the fastest route to hypothermia – and the first danger is not hypothermia at all. The Canadian cold-water researcher Gordon Giesbrecht summarised the phases as the 1–10–1 principle, which boating and water-rescue organisations teach widely:

• 1 minute – cold shock. Sudden immersion causes gasping and fast, uncontrolled breathing. Do not try to swim yet; keep your airway clear and concentrate on getting your breathing under control.
• 10 minutes – useful movement. Hands, arms and legs then lose strength and coordination quickly. This is roughly the time you have to get yourself out or onto something that floats.
• 1 hour – hypothermia. Even in very cold water it generally takes much longer than people think – in the order of an hour – before hypothermia makes an adult unconscious. With a life jacket, staying still and keeping as much of the body out of the water as possible buys time.

The figures are rough teaching numbers, not guarantees; water temperature, clothing, body build and a life jacket all change them. For bushcrafters the lesson is practical: wear a life jacket in canoes and on ice-cold lakes, do not cross rivers in spate, and stay off ice you cannot judge.

Once someone is out of the water, treat them as hypothermic even if they seem fine: out of the wind, wet clothes off and dry on in shelter, insulate, warm sweet drinks if fully alert. Expect delayed cooling – people often feel worse for a while after getting out, not better. Anyone who was in cold water for more than a few minutes, swallowed water or is confused needs the emergency services. Keep them lying down while you wait.

Frostbite first aid, trench foot and chilblains

Hypothermia is cooling of the whole body. Local cold injuries affect the parts furthest from the heart – fingers, toes, nose, ears, cheeks – and often occur together with it. If someone has both, hypothermia is treated first.

Frostnip and frostbite

The key rule for frostbite is: do not rewarm it if it could freeze again. Tissue that thaws and refreezes is damaged far more than tissue that stays frozen a little longer. In practice that means getting to a hut, a vehicle or a doctor first. There, guidance from wilderness medicine societies is to rewarm in a warm water bath of about 37–39 °C – it should feel comfortably warm to an uninjured hand or elbow, never hot – for roughly half an hour, until the skin is soft and its colour has returned. Rewarming hurts; that is normal.

• No rubbing, no massage, no snow. Frozen tissue is easily torn.
• No direct heat – fire, stove, radiator, hot-water bottle or heat lamp. Numb skin burns without warning.
• Do not burst blisters. Cover the area loosely with a dry, clean dressing and pad between fingers or toes.
• Do not walk on thawed feet if it can be avoided, and keep the affected part raised.
• See a doctor for anything beyond frostnip – how deep the damage goes cannot be judged in the field.

How to spot frostnip early on each other's faces is shown in the winter camping guide.

Trench foot (immersion foot)

Trench foot is a non-freezing cold injury: feet that stay wet and cool for many hours or days – in soaked boots, on long rainy trips, in a canoe – suffer nerve and vessel damage well above 0 °C. Signs are cold, numb, pale or blotchy skin, tingling and swelling, and pain when the feet warm up again. First aid is unspectacular: boots and wet socks off, dry the feet gently, let them warm slowly at air temperature in dry insulation, raise them – and no rubbing, no fire, no hot water. Get medical advice if numbness, colour change or blisters remain. Prevention is a routine: dry socks every night, feet aired at every long break, lacing not too tight. The full routine is in our footwear guide.

Chilblains

Chilblains are small, itchy or burning, red-to-purple swollen patches, usually on toes, fingers, ears or nose, that appear some hours after cold, damp exposure – often when cold skin has been warmed up too quickly. They are unpleasant but usually harmless and normally clear on their own within a few weeks. Keep the area warm and dry, do not scratch or rub, and do not put cold feet straight onto a heater or into hot water. See a doctor if they do not heal, break open or keep coming back.

Children and dogs in the cold

Children

Children cool faster than adults: they have more skin surface for their weight, smaller reserves, and they are often carried or sit still while the adults stay warm by walking. They also rarely say "I am cold" – they go quiet, whiny, clumsy or stop playing. Treat a child who has gone silent in cold, wet weather as a warning sign, check hands, neck and belly rather than asking, and act at the first shiver. Plan shorter days, feed them often, carry a complete change of clothes per child, and remember that a child in a carrier needs a layer more than you do. For anything beyond brief, mild shivering in a small child, call for medical advice early. More on safe trips with young ones in bushcraft with kids.

Dogs

Dogs get hypothermic too – especially small, lean, short-haired, old or very young dogs, and any dog that is wet and has to lie still at camp. Warning signs are persistent shivering, a tucked tail and hunched back, slowing down, reluctance to walk on, and later lethargy. Dry the dog, get it off the ground onto a pad or your pack, wrap it in a blanket or spare jacket and let it share your shelter. A dog that is listless, stiff or stops shivering while still cold needs a vet urgently. Check paws for ice balls and pads for cracks in snow, and pack a dog coat and a piece of foam mat for cold-weather overnighters.

Hypothermia myths that cause real harm

Most of these myths have one thing in common: they try to rewarm fast and from the outside in. Correct first aid does the opposite – it stops the losses, lets the body rewarm from the inside, and hands over to professionals when the body can no longer do that.