Temperature emergencies in the mountains kill people who didn’t see them coming. This is not because the warning signs are subtle — they aren’t. It’s because the warning signs are experienced by the person who is least equipped to interpret them accurately. A person developing hypothermia becomes confused and underestimates how cold they are. A person in heat stroke loses the rational capacity to recognise their own deterioration. Both conditions undermine the cognitive function needed to recognise and respond to themselves.

This is why the people around the patient are the critical observers — and why every hiker needs to be able to recognise these conditions in someone else, not just in theory but in the specific terrain and context where they actually develop.

Hypothermia: Cold That Comes Quietly

Hypothermia is defined as core body temperature below 35°C. The normal core temperature is 37°C — a drop of just 2°C produces the first clinical signs. It does not require extreme cold: hypothermia commonly develops at temperatures between 0°C and 10°C in wet, windy conditions with inadequate insulation. The common scenario is not a blizzard but a wet afternoon in summer, a hiker in a soaked cotton layer, resting too long at altitude after a warm ascent.

The stages and their signs

Field treatment: mild to moderate hypothermia

• Stop further heat loss first: get out of wind and rain; replace wet clothing with dry if available; wrap in insulation (sleeping bag, emergency bivvy, spare clothing from other group members)
• Add warmth carefully: warm sweet drinks if the person is conscious and can swallow safely; chemical heat packs to the axilla (armpits), groin and neck — never directly on skin; body-to-body warmth inside a sleeping bag is effective and underused
• Do not rub the extremities: rubbing cold limbs drives cold peripheral blood toward the core and can trigger cardiac arrhythmia; focus warmth on the core, not the hands and feet
• Do not give alcohol: alcohol causes peripheral vasodilation — the warmth feeling is real but the actual effect is increased heat loss from the core
• Call for rescue: mild hypothermia that is improving with shelter and insulation may not require evacuation; moderate or severe hypothermia always does — do not wait for full recovery before calling

Severe hypothermia: the “not dead until warm and dead” rule

A person in severe hypothermia may appear dead — no detectable pulse, no visible breathing, cold and stiff. Do not assume death in a hypothermic person who has not been rewarmed. Severe hypothermia produces a metabolic slow-down that can superficially mimic death. Begin CPR if there is no pulse, and do not stop until the person is rewarmed or a physician confirms death. People have been resuscitated after prolonged cardiac arrest in severe hypothermia who would have been considered dead in any other context.

Hyperthermia: The Mountain Heat Emergency

Hyperthermia is elevated core body temperature — the physiological opposite of hypothermia but equally dangerous. In mountain hiking it occurs most commonly in three scenarios: prolonged exertion in high summer heat (Corsica GR20, Pyrenees July–August), dehydration compounded by high UV exposure at altitude, and over-insulation in warmer-than-expected spring conditions.

Heat exhaustion vs. heat stroke: the critical distinction

Heat exhaustion: field treatment

• Move to shade immediately; stop all activity
• Lie down with legs elevated (improves blood flow to vital organs)
• Cool the skin: wet clothing, fan, shade
• Replace fluids with electrolyte solution (oral rehydration salts, sports drink, or water with a pinch of salt and sugar) — plain water alone dilutes remaining electrolytes
• Do not return to activity the same day; full recovery requires rest and monitoring

Heat stroke: immediate action

Heat stroke is a medical emergency. The core temperature is above 40°C and brain damage begins within minutes if not cooled. While calling rescue:

• Move to shade; remove excess clothing
• Cool aggressively: immerse in any available water source (stream, lake); apply ice or snow to armpits, groin and neck; wet the skin and fan continuously
• Do not give fluids to an unconscious or confused person — aspiration risk
• Recovery position if unconscious and breathing
• Do not stop cooling until emergency services arrive or core temperature is clearly falling (person becomes coherent and skin cools)

Prevention: The Same System Applies to Both

Hypothermia and hyperthermia are temperature regulation failures — both preventable by the same discipline: monitor your group’s condition continuously, not just your own. The person developing hypothermia is the least able to notice it; the person in early heat stroke is too confused to accurately report their own state. Designate one person per group as the designated condition monitor — their job is to watch the others for signs of thermal stress at every rest stop. Check: are they shivering or sweating abnormally? Is their speech normal? Do they seem unusually fatigued or confused for the effort level?

Hydration is the common prevention thread: both heat exhaustion and cold-weather hypovolaemia (low blood volume from inadequate drinking) reduce the body’s ability to regulate temperature. Drink before you feel thirsty — thirst is a lagging indicator that appears after fluid deficit is established. On cold days, the sensation of thirst is further suppressed; cold air is dry and respiratory fluid losses are significant even when you don’t feel like drinking.