Altitude Sickness & Acclimatisation

Altitude sickness (acute mountain sickness, AMS) can affect anyone above about 2,500 m, regardless of age or fitness. It happens when you climb faster than your body can adapt to the lower oxygen. The good news: with a slow ascent, rest days and a guide who knows the signs, it is almost always preventable and manageable.

Symptoms

Mild AMS is common and feels like a hangover:

• headache
• loss of appetite or nausea
• tiredness and poor sleep
• dizziness

Serious altitude illness is an emergency:

• HAPE (fluid in the lungs): breathlessness at rest, a wet cough, unusual weakness.
• HACE (swelling of the brain): confusion, loss of coordination, severe headache, drowsiness.

Anyone with these symptoms must descend immediately.

How our itineraries prevent it

• Above 3,000 m we aim to raise sleeping altitude by no more than about 300–500 m a day.
• We build in rest days for acclimatisation — for example in Namche and Dingboche on the Everest Base Camp Trek and in Manang on the Annapurna Circuit.
• “Climb high, sleep low”: day hikes to higher viewpoints, then back down to sleep.
• Your guide checks how everyone feels morning and evening and carries a group first-aid kit.

What you can do

1. Walk slowly — you should be able to talk while climbing.
2. Drink 3–4 litres of water a day.
3. Avoid alcohol and sleeping pills at altitude.
4. Tell your guide about symptoms early. There is no shame in a slower day.
5. Ask your doctor about acetazolamide (Diamox) before you travel.

If someone gets ill

Mild symptoms: rest at the same altitude until they pass. Worsening symptoms: descend 300–500 m, which usually brings fast relief. Serious symptoms: immediate descent and, if needed, helicopter evacuation — which is why your travel insurance must cover it.

This guide is general information, not medical advice. Talk to a travel doctor before your trip, especially if you have heart or lung conditions.