Altitude sickness on the Everest trek: the simple rules that keep you safe

Altitude — not the walking — is the real challenge of an Everest trek. Here are the proven rules, and the warning signs, every trekker should know before 2026.

LR By Laxman Rawal · Jun 25, 2026 · 3 min read · Updated Jun 17, 2026 · ▶ Web Story

Larke Pass (5,106 m) on the Manaslu Circuit — high-altitude Himalayan trekking

Here is the truth most first-time trekkers underestimate: the hard part of the Everest Base Camp trek is not the distance or the steepness — it is the thin air. Above 3,000 metres your body has to adapt to roughly half the oxygen it is used to, and rushing that process is what makes people sick. The good news is that altitude sickness is largely preventable if you follow a few well-proven rules.

From the trail · Everest

Altitude sickness on the Everest trek — Everest, Nepal

Know the basics

Symptoms of mild AMS: headache, nausea, poor sleep, fatigue
The golden rule: climb high, sleep low, and ascend slowly
Build in acclimatisation days (Namche, Dingboche on the EBC route)
If symptoms worsen, the only sure cure is to descend

The rules that work

Acclimatisation is not optional — it is the whole game. Above about 3,000m, aim to raise your sleeping altitude only gradually each day, and take rest days where the classic itineraries put them (a good Everest trek schedules acclimatisation days at Namche Bazaar and Dingboche for exactly this reason). Hydrate hard, walk slowly, eat well, and never ignore a worsening headache. Many trekkers carry acetazolamide (Diamox) as a preventive — discuss it with your doctor. Above all, respect the mountain's timetable, not your own.

Altitude rules for the Everest trek
Rule	Why it matters
Ascend slowly above 3,000m	Gives your body time to adapt
Climb high, sleep low	Trains the body without overnight stress
Take acclimatisation days	Namche & Dingboche exist for this
Descend if it gets worse	The one reliable cure for serious AMS

What this means for you

You do not need to fear altitude — you need to respect it. Our Everest itineraries are built with the right acclimatisation days and guides trained to spot early symptoms, so you ascend at a pace your body can handle. Choose a properly paced trek, and the thin air becomes a challenge you are ready for, not a gamble.

The three altitude illnesses — and the numbers that prevent them

"Altitude sickness" is really three conditions on one spectrum. AMS (acute mountain sickness) is the common, mild form — headache, nausea, poor sleep. Left unchecked it can progress to the two dangerous ones: HACE (fluid on the brain — confusion, loss of balance) and HAPE (fluid in the lungs — breathlessness at rest, a wet cough). HACE and HAPE are medical emergencies and the response to both is immediate descent. The reassuring part: both are rare on a properly paced trek, because pacing is the whole defence.

300–500 mmax sleeping-altitude gain per day above 3,000 m

~1,000 mtake a full rest day for every gain of

3–4 Lwater per day to aid acclimatisation

Descendthe one reliable cure for HACE / HAPE

Standard guidance above 3,000 m is to raise your sleeping altitude by no more than 300–500 m a day and to build in a rest day roughly every 1,000 m — exactly why good Everest itineraries pause at Namche and Dingboche. Diamox (acetazolamide) can help prevent and ease symptoms; discuss it with your doctor before you travel. And the cardinal rule never changes: if symptoms are getting worse, you go down, not up.

Source: Travel Himalaya Nepal; CIWEC Clinic / UIAA altitude guidance.

Source: Travel Himalaya Nepal

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