Altitude illness is the main medical risk on a Himalayan trek, and it is largely preventable. It is also poorly understood by most first-time trekkers, who assume fitness protects them. It does not — if anything, fit trekkers are at slightly higher risk because they climb faster.
What causes it
Above roughly 2,500m the air holds progressively less oxygen. Your body compensates over days by producing more red blood cells and changing your breathing pattern. Ascend faster than that adaptation and fluid begins shifting into places it should not be — the brain and the lungs. That is the whole mechanism, and the fix is always the same: go up more slowly, or come down.
Mild symptoms (AMS)
Headache, poor sleep, loss of appetite, nausea, mild dizziness and general fatigue. These are common above 3,000m and usually resolve with a rest day, hydration and no further ascent. Tell your guide. Every guide we employ carries a pulse oximeter and checks the whole group twice daily above 4,000m — but the symptom report has to come from you.
Serious symptoms — descend immediately
Loss of coordination (being unable to walk a straight line), confusion, severe headache unrelieved by painkillers, breathlessness at rest, a persistent wet cough, or blue lips and fingertips. These indicate high-altitude cerebral or pulmonary oedema. Descent is the treatment. Not rest, not oxygen alone, not waiting until morning.
Prevention that actually works
- Choose an itinerary with real acclimatisation days. Our fifteen-day Everest schedule includes two; twelve-day itineraries do not, and that is the single biggest risk factor a trekker can control at the point of booking.
- Climb high, sleep low. Acclimatisation hikes exist for this reason — Nangkartshang Peak from Dingboche, Ice Lake from Manang.
- Hydrate. Three to four litres a day at altitude.
- No alcohol above 3,000m, and go easy on sleeping tablets.
- Discuss Diamox (acetazolamide) with your doctor before you travel. It helps, but it is not a licence to ascend faster.
Whose call is it?
Your guide's. If they decide a member of the group descends, that decision is final and not open to negotiation — including on the day you were meant to reach Base Camp. Every trekker on our routes must carry insurance covering helicopter evacuation to 6,000m.
If you are new to altitude, start below 4,200m: the Annapurna Base Camp Trek or the Ghorepani Poon Hill Trek are the two we recommend most often.
