Altitude Sickness: Recognizing AMS, HACE, and HAPE — and When to Descend
Altitude sickness is about ascent speed, not fitness. Learn to tell a watchable AMS from the two emergencies — HACE and HAPE — and when the only move is down.
Altitude sickness is about ascending too fast, not about poor fitness. AMS feels like a hangover — a headache plus loss of appetite, dizziness, fatigue or nausea, arriving 2–12 hours after you reach altitude — and usually resolves in 1–3 days if you stop sleeping higher. HACE and HAPE are different: unsteady walking, confusion, or breathlessness at rest means descend immediately, whatever the summit plans said.
Altitude illness is not a verdict on your fitness. The strong suffer as readily as the unfit, and the only reliable predictor is your own history — and even that is not absolute.
Telling Them Apart
| Condition | What it looks like | What to do |
|---|---|---|
| AMS (acute mountain sickness) | Headache plus loss of appetite, dizziness, fatigue, or nausea, showing up 2–12 hours after arrival — like a bad hangover | Usually resolves in 1–3 days; do not sleep at a higher elevation once symptoms appear |
| HACE (high-altitude cerebral edema) | Unsteady walking, confusion, drowsiness, slurred or irrational speech | An emergency — descend now, don't wait |
| HAPE (high-altitude pulmonary edema) | Unusual breathlessness on exertion, dry cough, breathlessness at rest, pink frothy sputum | An emergency — descend and call for help now; kills faster than HACE |
Prevention Matters More Than Pills
- Don't go from low elevation to sleeping above 9,000 ft (2,750 m) in a single day.
- Above 9,800 ft (3,000 m), gain no more than 1,600 ft (500 m) of sleeping altitude per day, and add one acclimatization night for every 3,300 ft (1,000 m) gained.
- First 48 hours at altitude: no alcohol, no hard exercise, drink plenty of water. If you drink coffee daily, don't stop suddenly — a withdrawal headache muddies the assessment.
- Fitness doesn't protect you. Your own history of altitude illness is the best reference — but it isn't absolute.
What to Do
- Mild AMS: rest in place, hydrate, take pain relief as directed, and stop ascending. If it worsens, go down.
- Unsteady walking, altered consciousness, breathlessness at rest, or pink frothy sputum: descending comes first — call for help at the same time, and use oxygen if you have it.
- Drugs like acetazolamide and dexamethasone are a physician's decision. Don't borrow someone else's, don't improvise doses, and talk to a doctor first if you have underlying conditions, are pregnant, or this is a child.
Common Mistakes
- "Just push on to camp and it'll be fine" — HACE and HAPE worsen in exactly that push.
- Writing it off as a cold or a hangover and continuing upward.
- Carrying an oxygen canister but never learning the descent route — a small canister doesn't last long.
This is not medical advice. Severe symptoms mean descending and contacting local rescue or a physician.