Altitude and Acclimatization

Altitude sickness can affect trekkers regardless of fitness level — it is caused by ascending faster than the body can adapt to lower oxygen levels, not by lack of physical conditioning.

The standard guidance above 3,000 m is to avoid increasing sleeping altitude by more than roughly 300-500 m per day, with a rest day roughly every 1,000 m of gain. This is why routes like Everest Base Camp and Annapurna Circuit build in dedicated acclimatization days at Namche/Dingboche and Manang.

Early symptoms include headache, nausea, fatigue and disturbed sleep. These are common and usually resolve with rest at the same altitude. The rule that matters most: never continue ascending if symptoms are worsening, and descend immediately if symptoms become severe (confusion, loss of coordination, or breathlessness at rest).

Staying well hydrated, avoiding alcohol during the trek, and pacing walking speed to conversation level (rather than pushing hard) all reduce the risk of acute mountain sickness.

A guide experienced on your specific route is one of the most effective safety measures available, since they can recognize warning signs and make an objective call to descend when a trekker might be inclined to push through.