Altitude sickness, also called acute mountain sickness or AMS, can affect any trekker at height, whatever their fitness. This guide covers the basics of how to reduce the risk and what to do if symptoms start. It is general information and not medical advice. Talk to a doctor before a high-altitude trek, especially if you have a heart, lung or other health condition.
Why it happens
As you go higher the air holds less oxygen, and the body needs time to adjust. Going up too fast is the main cause. Sources commonly put the point where care is needed at around 2,500 m.
How to reduce the risk
- Go up gradually. Above about 3,000 m, try to raise your sleeping altitude by no more than 300 to 500 m a night.
- Plan an acclimatisation day after any large gain in height.
- Climb high, sleep low: walk to a higher point in the day, then return to sleep lower.
- Drink plenty of water, commonly suggested at 3 to 4 litres a day, and eat well.
- Avoid alcohol and smoking, and avoid sleeping pills.
- Choose an itinerary that gives you time. Rushing is the most common reason people get sick.
Early signs
Headache, nausea, tiredness and poor sleep are common early signs. If you notice them, stop going higher, rest, drink water and tell your guide. Do not push through, and do not assume it is just tiredness.
Danger signs: go down now
Confusion, severe breathlessness at rest, loss of balance or coordination, or a worsening headache can signal severe altitude illness (HAPE or HACE). The standard response is to descend immediately and get medical help. Do not wait for morning.
Medicines
Some people use acetazolamide (often sold as Diamox) to help prevent altitude sickness. Only take medicine like this on a doctor's advice. It does not replace gradual ascent.
Before you book
- Ask your operator how the itinerary handles acclimatisation and where you sleep each night.
- Ask what the evacuation plan is, who carries oxygen or a first-aid kit, and how far the nearest road and hospital are.
- Check the AMS risk and difficulty shown on the trek page.
Sources and how to read this page
This guide paraphrases the sources below. It is general information, so follow your doctor and your guide, and treat the numbers as rules of thumb.