Cold kills slowly and then very suddenly, and almost every instinct people have about warming someone up is either useless or actively dangerous.
1. Recognising how cold they are
| Stage | Core temperature | What you see |
|---|---|---|
| Mild | 32–35 °C | Shivering, and still able to help themselves. Cold, clumsy hands, slurred speech, poor judgement, withdrawn or oddly irritable |
| Moderate | 28–32 °C | Shivering stops — which is a deterioration, not an improvement. Confusion, drowsiness, stumbling, mumbling. Slow pulse and breathing |
| Severe | Below 28 °C | Unresponsive, rigid, pulse and breathing very slow and hard to find, pupils may be dilated. Can be mistaken for dead |
The moment shivering stops is the moment to worry. Shivering is the body's heat production working; its absence in someone still cold means the reserve has gone. People routinely read it as “they've settled”. Along with it come the two behavioural signs that precede collapse: irrational behaviour and paradoxical undressing — someone hypothermic may insist they are hot and start removing clothes.
2. What to do
Move them gently, and keep them horizontal
This is the instruction most likely to be ignored and it matters most. Below about 30 °C the heart is prone to fibrillate, and rough handling, dragging, or standing someone upright can trigger it. Do not sit them up, and do not let them help carry themselves. Lift horizontally, support the head, move slowly. If they must be moved by one person, accept a slower move rather than a rougher one.
The walking rule, scoped — because “never walk a hypothermic person” is too broad and gets applied where it does harm. Someone with mild hypothermia who is shivering, lucid and steady on their feet should usually walk to shelter if it is close: muscle activity generates heat, and standing about waiting for a stretcher in the cold is worse than a short walk. The prohibition applies once shivering has stopped, or if they are confused, drowsy, stumbling or in any way not fully themselves — that is the point at which the heart becomes irritable and exertion becomes the risk. If you are unsure which group they are in, treat them as the second.
Get them out of the cold and out of wet clothing
Cut clothing off rather than pulling it over the head if that is gentler. Wet fabric strips heat far faster than air does. Shelter first, even an imperfect one.
Insulate everything, including the head, and put something underneath them
Blankets, sleeping bag, coats, foil blanket, dry clothing. The ground conducts heat away faster than air, so insulation beneath them matters as much as on top — roll mat, rucksack, cardboard, spare coats.
Warm the core, not the extremities
Heat packs or warm water bottles wrapped in cloth to the chest, armpits, neck and groin. Never directly on skin. Do not put a hypothermic person in a hot bath and do not rub their arms and legs — both dilate cold peripheral vessels, returning chilled blood to the heart and dropping the blood pressure.
Warm sweet drinks only if fully alert and able to swallow
And no alcohol, which feels warming precisely because it dilates skin vessels and loses heat faster. Nothing by mouth if drowsy.
999 for anything beyond mild, and for everyone who has stopped shivering
Severe hypothermia needs rewarming that only a hospital can do, sometimes on a bypass or ECMO circuit.
Afterdrop, and why someone can deteriorate after rescue
- Core temperature often continues to fall for a while after someone is brought into the warm. Cold blood held in the limbs returns to the trunk as the peripheries open up, so the reading drops even as the room gets warmer.
- Rewarming collapse is the same mechanism hitting the circulation: vessels dilate, the effective blood volume is suddenly too small for the space, and the blood pressure falls. It is a recognised cause of death during rescue rather than before it.
- Which is the real reason for handling gently, keeping them flat, and warming the trunk rather than the limbs. Those three instructions are not caution for its own sake; they are all aimed at this.
- It is also why a hypothermic person is not "out of danger" once indoors, and should not be left to warm up unattended.
3. If they are unresponsive
- Take longer to check. Pulse and breathing may be extremely slow and faint — look, listen and feel for a full minute rather than ten seconds before concluding there is no output.
- If there is no breathing, start CPR and follow the resuscitation chapter. Compressions and shocks work less well in a cold heart, which is a reason to continue rather than to stop.
- Continue far longer than usual. Survival with full neurological recovery has followed prolonged resuscitation in deep hypothermia. Rewarming and resuscitation happen together, in hospital.
- Say the word hypothermia on the phone, and say how long they were exposed and whether they were in water. It changes the destination, because not every hospital can rewarm on a circuit.
- Do not conclude death at the scene in a cold patient unless there are injuries obviously incompatible with life. That decision belongs to a clinician after rewarming.
4. Frostbite and non-freezing cold injury
| Do | Do not |
|---|---|
| Get out of the cold, remove rings and wet gloves or boots, and treat the whole person for hypothermia first — that always outranks the fingers Rewarm rapidly in water at 37–39 °C — comfortably warm to an uninjured hand — for 20 to 30 minutes, until the tissue is red and pliable Ibuprofen if there is no reason to avoid it Dress loosely, separate the digits, elevate, and get it seen |
Rub or massage it, or use snow — ice crystals in the tissue will shear it apart Use direct heat — fire, radiator, hairdryer, exhaust. Frozen skin cannot feel a burn and gets one Thaw it if there is any chance of it refreezing before definitive care. A refrozen thawed extremity does far worse than one kept frozen a little longer — so on a mountain, keep going and thaw at the bottom Burst the blisters Walk on thawed feet |
Non-freezing cold injury — trench foot — is a different thing and is easier to miss, because the tissue never freezes. Hours to days in cold wet conditions produce numb, white, wrinkled, swollen feet that become intensely painful on rewarming. The treatment is dry, gradual warming at room temperature, elevation and analgesia. Not rapid rewarming, which is agonising and unhelpful here, and the pain can persist for months.