What to do
Prevent it (ascend gradually)
- 1Don't go "too high, too fast" — avoid jumping from low altitude straight to a high sleeping altitude in one day.
- 2Up high, raise your sleeping altitude slowly — roughly no more than about 1,600 ft per night — and take an extra rest/acclimatization day for each ~3,300 ft gained.
- 3"Climb high, sleep low" — you can go higher during the day but sleep lower.
- 4Avoid alcohol the first couple of days, do only mild exercise early, stay hydrated, and avoid respiratory-depressant substances.
- 5A prescription medication to speed acclimatization exists for people who must ascend abruptly — that's a decision for a healthcare provider, not a field step.
If someone develops it
- 1Recognize AMS — a headache at altitude plus nausea, fatigue, dizziness, or bad sleep.
- 2Stop ascending. Don't go higher while symptomatic; rest and hydrate and let mild AMS improve.
- 3If symptoms get worse, or don't improve, descend — going down is the most reliable treatment.
- 4For any sign of HACE (confusion, stumbling) or HAPE (breathlessness at rest, wet cough, blue lips): descend immediately and get emergency care — these are life-threatening and every hour matters.
When to use it
- High-adventure treks and mountain travel — Philmont, western peaks, any trip that gains serious altitude.
- Recognizing that a "just a headache and tired" scout on day one may have AMS and shouldn't be pushed higher.
- Planning an itinerary with acclimatization days built in, not just mileage.
Common mistakes & safety
- The three golden rules: learn to recognize AMS; never ascend with worsening symptoms; if symptoms are severe or getting worse, descend. Following these prevents most altitude deaths.
- HACE and HAPE are emergencies — descend now. Don't wait, don't "sleep on it," don't push to a summit; descent is the definitive treatment and delay kills.
- Fitness does not protect you. A strong athlete isn't at lower risk, and children are as susceptible as adults. Anyone can get it.
- Don't blame the headache on dehydration and push on. Treat a headache at altitude as possible AMS and stop ascending until it clears.
- Watch each other, especially for the mental-status and coordination changes of HACE, which the affected person often can't judge in themselves.
- Cold, sun, and dehydration stack on top at altitude — they make everything worse.
Going deeper
- AMS feels like a hangover — headache, nausea, fatigue, poor sleep — which is why it's easy to dismiss on day one at altitude.
- HACE is the brain, HAPE is the lungs. HACE shows up as acting drunk (confusion, can't walk straight); HAPE shows up as can't catch your breath even at rest with a wet cough. Either means go down.
- Why "climb high, sleep low" works. The body is stressed most while sleeping at altitude — daytime height with a lower sleeping altitude acclimatizes you with less risk.
Official source
High-altitude travel and altitude illness — CDC Yellow Book →This is general information, not a substitute for medical advice or training. HACE and HAPE are life-threatening — descend and get emergency care.