What Every Mountaineer Must Know Mountain Illness

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Acute Mountain Sickness & Cold Injuries: What Every Mountaineer Must Know

A comprehensive, evidence-based survival guide covering AMS, HACE, HAPE, frostbite, and hypothermia — based on the latest Wilderness Medical Society 2024 guidelines and NIH research.

By Mountain Safety Editorial  |  Updated: April 2026  |  8 min read  |  Sources: WMS 2024, NIH StatPearls 2025, Adventure Medic 2025, UIAA 2025

 

The mountain does not negotiate. Every year, hundreds of trekkers and climbers across the Himalayas, the Andes, and the Alps are struck down not by avalanches or falls, but by the invisible physiological forces of altitude and cold — forces that kill quietly, progress rapidly, and are almost entirely preventable with the right knowledge. According to the NIH's updated StatPearls reference (September 2025), approximately 200 million people travel to high-altitude destinations every year, and acute mountain sickness (AMS) is now one of the most common medical conditions encountered in outdoor recreation. Yet studies consistently show that most victims neither recognised the warning signs nor knew how to respond.

This guide covers everything a mountaineer — from a Himalayan trekker to an Alpine alpinist — needs to know about altitude illness and cold injuries: what causes them, how to recognise them before they become life-threatening, and exactly what to do when they strike.

⚠  Critical Rule:  If symptoms of serious altitude illness or severe cold injury appear, DESCEND immediately. Descent is the definitive treatment. Never ascend with symptoms.

PART ONE: Altitude Illness — Understanding the Invisible Enemy

What Is Acute Mountain Sickness (AMS)?

AMS is the body's distress signal when it ascends faster than it can adapt to thinning air. At altitude, atmospheric pressure drops — and with it, the partial pressure of oxygen your body can extract from each breath. Above 2,500 metres (8,200 ft), the risk begins. Above 3,000 metres, the daily ascent rate should not exceed 500 metres per night to allow proper acclimatisation.

The condition typically begins 4 to 12 hours after arrival at altitude (and up to 72 hours later in some cases). The pathophysiology involves hypoxia-induced cerebral vasodilation, mild interstitial brain oedema, and increased sympathetic activity — in plain terms, your brain swells slightly in response to insufficient oxygen.

Recognising AMS: The Lake Louise Scoring System

The internationally accepted diagnostic tool is the Lake Louise Scoring System (LLSS), used by wilderness physicians worldwide. AMS is diagnosed when altitude-related headache is present alongside at least one of the following:

•         Nausea or vomiting

•         Fatigue or weakness

•         Dizziness or lightheadedness

•         Difficulty sleeping

 

Scores from 3 to 5 indicate mild to moderate AMS; scores of 6 to 9 represent moderate to severe AMS. The crucial action: do not ascend further until all symptoms have completely resolved.

The Deadly Escalations: HACE and HAPE

If AMS is ignored and ascent continues, it can escalate into two life-threatening conditions — and both can kill within hours of onset.

HACE (High Altitude Cerebral Oedema):  The most severe form of altitude illness — characterised by altered mental status and loss of coordination (ataxia). Untreated HACE can be fatal within 24 hours. Immediate descent is non-negotiable. Dexamethasone 8 mg (injection if available) is the primary drug treatment. A portable hyperbaric chamber (Gamow bag) can simulate descent if evacuation is delayed.

 

HAPE (High Altitude Pulmonary Oedema):  Fluid accumulates in the lungs, causing breathlessness at rest, dry cough, pink frothy sputum, and severe fatigue. HAPE is the leading cause of altitude-related death. Immediate descent of at least 500 metres is critical. Nifedipine (10–20 mg chewed, then 20–30 mg long-acting every 12 hours) is the field treatment of choice. Supplemental oxygen if available.

 

Prevention: The Golden Rules of Acclimatisation

The Wilderness Medical Society (WMS) 2024 updated guidelines and the Evidence-Based Medicine Guidelines (2025) are unambiguous: gradual ascent is the single most effective prevention strategy.

•         Ascend no more than 500 metres per night above 3,000 metres

•         Rest one full day for every 1,000 metres gained above 3,000 metres

•         Follow the climber's mantra: 'Climb high, sleep low'

•         Stay well hydrated — dehydration compounds altitude illness risk

•         Avoid alcohol, sleeping pills, and sedatives, which suppress respiratory drive

•         Consider acetazolamide (Diamox, 125–250 mg twice daily) prophylactically — consult a doctor before your expedition

•         Know your personal history: prior AMS significantly increases your risk

PART TWO: Cold Injuries — When Temperature Becomes the Threat

Cold injuries are among the most common emergencies facing mountaineers at altitude. A landmark survey of mountaineers found that the incidence of frostbite was 366 cases per 1,000 individuals per year — and the three leading causes were inappropriate clothing, incorrect or absent equipment, and lack of knowledge about cold exposure. The last of these is fully within your control.

Frostnip: The Warning Shot

Frostnip is the precursor to frostbite — a superficial, non-freezing cold injury affecting exposed skin (ears, nose, cheeks, fingertips). Ice crystals form on the skin surface but not within the tissue. Skin turns pale or red and becomes numb, but no permanent damage occurs if treated immediately. Action: rewarm with direct body heat, cover the skin, seek shelter. Frostnip is the body's first warning. Ignore it at your peril.

Frostbite: When Tissue Freezes

Frostbite occurs when tissue temperature drops below freezing, causing ice crystal formation inside cells, disruption of cell membranes, and eventually cell death. The WMS 2024 Frostbite Guidelines describe three clinical phases: the pre-freeze phase (vasoconstriction, paraesthesia), the freeze-thaw phase (ice crystal formation, cell death, inflammatory response), and the vascular stasis phase (blood vessel damage, intravascular coagulation).

Frostbite most commonly affects the feet, hands, nose, ears, and chin — all areas of reduced circulation and high surface-to-volume exposure. Severity is classified into four grades: Grade 1 (superficial, no tissue loss), Grade 2 (partial thickness, blistering), Grade 3 (full thickness, haemorrhagic blisters), and Grade 4 (full thickness with bone involvement).

Field Treatment of Frostbite — What the 2024 Guidelines Say

The updated WMS and Adventure Medic 2025 guidance is precise about what to do — and crucially, what not to do — in the field:

•         DO NOT rewarm if there is any risk of refreezing — refreezing causes catastrophically worse tissue damage than remaining frozen

•         DO protect frozen tissue from trauma; pad and bandage loosely

•         DO treat hypothermia first — moderate to severe hypothermia must be addressed before frostbite

•         DO rewarm in warm water (37–39°C) for 15–30 minutes once evacuation to safety is assured

•         DO NOT rub or massage frostbitten tissue — this destroys cells

•         DO NOT pop haemorrhagic (blood-filled) blisters in the field

•         DO commence ibuprofen 400 mg three times daily to reduce the inflammatory response

•         In hospital: iloprost IV is now the first-line therapy for Grade 3–4 frostbite within 48 hours of thawing

Hypothermia: The Silent Killer

Hypothermia — a core body temperature below 35°C — is a risk at any altitude in cold, wet, or windy conditions, and it frequently accompanies frostbite. The WMS guidelines classify hypothermia as mild (32–35°C), moderate (28–32°C), and severe (<28°C). Mild symptoms include shivering and confusion; severe hypothermia produces loss of shivering (paradoxically a dangerous sign), unconsciousness, and cardiac arrhythmia.

Field management focuses on preventing further heat loss: remove wet clothing, insulate from the ground, shelter from wind, apply heat packs to axillae and groin (not extremities), provide warm sweet drinks if the patient is conscious. In severe cases, handle the casualty gently — cold hearts are prone to ventricular fibrillation with rough movement. Modern guidance from the WMS emphasises that hypothermia patients who appear dead should be considered 'not dead until warm and dead' — successful resuscitation after prolonged cardiac arrest in hypothermic patients is documented.

Quick Reference: Altitude Illness & Cold Injury at a Glance

Condition	Key Signs	Immediate Action
AMS (mild)	Headache, nausea, fatigue, poor sleep	Stop ascending. Rest. Hydrate. Ibuprofen/paracetamol for headache.
AMS (severe)	Above + impaired function, vomiting	Descend minimum 500 m. Acetazolamide 250 mg. No further ascent.
HACE	Ataxia (stumbling), confusion, altered consciousness	IMMEDIATE descent. Dexamethasone 8 mg. Gamow bag if available.
HAPE	Breathlessness at rest, cough, frothy sputum	IMMEDIATE descent. Nifedipine. O₂ if available.
Frostnip	Pale/numb skin, no tissue damage	Rewarm with body heat. Cover skin. No blisters present.
Frostbite	Pale/waxy skin, numbness, blistering	Do NOT rewarm if refreeze risk. Pad and evacuate.
Hypothermia	Shivering, confusion, cold skin	Insulate. Remove wet clothes. Gentle handling. Warm drinks if alert.

 

Before You Go: Your Pre-Expedition Medical Checklist

•         Consult a travel or wilderness medicine physician before any high-altitude expedition

•         Discuss acetazolamide (Diamox) prophylaxis — especially for rapid ascent profiles or if you have prior AMS history

•         Carry a pulse oximeter to monitor blood oxygen saturation (SpO₂) throughout your ascent

•         Carry dexamethasone and nifedipine in your expedition medical kit (with training in their use)

•         Pack a Gamow (portable hyperbaric) bag for expeditions above 5,000 m

•         Learn to recognise ataxia — the heel-to-toe walk test is a critical field assessment for HACE

•         Layer clothing correctly: moisture-wicking base layer, insulating mid-layer, windproof/waterproof outer shell

•         Never summit in deteriorating weather — most cold injuries happen during storm delays

 

The mountains will always be uncompromising. But the difference between a life-ending emergency and a safe descent is almost always knowledge — knowing the signs, acting early, and never letting summit fever override the body's signals. Every death from AMS, HACE, HAPE, or cold injury on the world's high peaks represents a tragedy that current medical knowledge could have prevented. Carry this knowledge with you. It weighs nothing, and it may save everything.

 

MEDICAL DISCLAIMER: This article is for educational purposes only and does not constitute medical advice. Always consult a qualified physician before high-altitude travel. In any medical emergency, descend immediately and seek professional medical care.

SOURCES: Wilderness Medical Society Clinical Practice Guidelines 2024 (Altitude Illness & Frostbite); NIH StatPearls — Acute Mountain Sickness (updated Sept 2025); Evidence-Based Medicine Guidelines — Acute Mountain Sickness (2025); Adventure Medic — Frostbite Prevention & Management 2025; UIAA Medical Commission 2025; Emergency Care for High-Altitude Trekking & Climbing, SAGE Journals 2025; PMC — Exercise in the Cold: Preventing and Managing Hypothermia and Frostbite Injury.

Tags: #AMS  #AltitudeSickness  #Frostbite  #Hypothermia  #HACE  #HAPE  #MountainSafety  #HimalayanTrekking  #WildernessMedicine  #MountaineeringHealth