Understanding altitude sickness

Published 5 March 2026

Above roughly 2,500m, the air holds progressively less oxygen, and your body needs time to adapt. Acute Mountain Sickness (AMS) — headache, nausea, fatigue, poor sleep — is common and usually manageable; the serious complications (HAPE and HACE) are rare when a sensible itinerary is followed, but they're the reason every reputable operator builds in rest days rather than racing to altitude.

The golden rule is simple: climb high, sleep low where possible, and never ascend more than about 300–500m in sleeping altitude per day above 3,000m, with a full rest/acclimatisation day roughly every 3–4 days. Every itinerary we run is built around this pattern — including the well-known rest days at Namche Bazaar and Dingboche on the Everest route.

Hydration matters more than most people expect — 3-4 litres a day — and it's worth avoiding alcohol and sleeping pills at altitude, since both can mask or worsen symptoms. Your guide will check in daily and carries a pulse oximeter to track your blood oxygen saturation; a dropping trend is the earliest and most reliable warning sign, well before you'd feel seriously unwell.

The single most important thing to know: mild AMS symptoms are common and not a reason to panic, but they are always a reason to tell your guide immediately. The only real treatment that matters if symptoms worsen is descent, and it works fast — most people feel dramatically better within a few hundred metres of losing altitude.