Hiking at High Altitude: How to Acclimatise Well
Altitude affects everyone differently, and fitness offers little protection. Here's how to acclimatise, spot the warning signs and stay safe.
Above roughly 2,500 m (8,200 ft), the lower air pressure means less oxygen reaches your body with each breath. Your body can adapt — but it needs time. Altitude illness can affect anyone, regardless of age or fitness.
The golden rules of acclimatisation
- Ascend gradually. Above 3,000 m, try not to increase your sleeping altitude by more than 300–500 m per night.
- Build in rest days. Take a rest or acclimatisation day every three to four days, or every 1,000 m of sleeping gain.
- Climb high, sleep low. Hiking higher during the day and returning lower to sleep helps your body adapt.
- Stay hydrated and eat well. Your appetite may drop; keep eating anyway.
- Avoid alcohol and sleeping pills in the first few days at altitude.
Know the signs
Acute Mountain Sickness (AMS)
Headache plus one or more of: nausea, fatigue, dizziness, poor sleep or loss of appetite. It feels a lot like a hangover. Don’t go higher until symptoms resolve. If they get worse, descend.
High Altitude Cerebral Oedema (HACE)
Confusion, loss of coordination (stumbling, can’t walk a straight line), severe headache, drowsiness. This is a medical emergency — descend immediately.
High Altitude Pulmonary Oedema (HAPE)
Breathlessness at rest, a persistent cough, gurgling breath, extreme fatigue. Also a medical emergency — descend immediately.
Medication
Some trekkers use acetazolamide to help acclimatisation. Speak to a doctor with travel-medicine experience before your trip about whether it’s appropriate for you.
The most important rule
Never ascend with symptoms, and descend if they get worse. Mountains will wait. Descending even a few hundred metres often brings rapid relief.