The short answer
Above about 2,500 metres the air has less oxygen, and some people get altitude sickness. The main protections are a gradual ascent, rest days, drinking enough water, eating regularly and listening to symptoms. A common guideline is to increase your sleeping height slowly above 3,000 metres and include a rest day every few days, and to "climb high, sleep low" when you can.
Mild symptoms such as headache, poor appetite and trouble sleeping are common. If they get worse, or you have severe headache, vomiting, confusion, unsteady walking or breathlessness at rest, stop ascending and go down immediately and seek help. Ask your doctor before the trip about preventive medicine and carry insurance that covers evacuation.
Key facts
- Rule
- Ascend gradually, rest days
- Mild signs
- Headache, poor sleep
- Danger signs
- Confusion, unsteady, breathless at rest
- Action
- Descend and get help
How it works
- Plan the profileGradual sleeping heights.
- Hydrate and eatRegularly.
- Know the signsMild and severe.
- Stop ascending if worseDo not push.
- Descend if seriousImmediately.
How altitude affects the body
As you go higher, each breath contains less oxygen. Most people feel a little breathless, sleep poorly or get a mild headache at first. These effects often ease as the body adapts, which takes days rather than hours.
Fitness helps with stamina but does not prevent altitude illness. Young and fit people can be affected just like others, so pace matters more than strength.
When to be careful
Mild symptoms deserve rest and observation. If symptoms worsen, such as a strong headache, vomiting, confusion, loss of balance or breathlessness at rest, stop going up and descend with help. Do not leave an unwell person alone.
Talk to your doctor before travel, especially if you have heart, lung or blood conditions, and agree an emergency plan with your operator. This guide is general information, not medical advice.
Insider tip
Never leave a person with worsening symptoms alone; descend with them.
Avoid this
Do not take medicine to mask symptoms and keep climbing.
Related questions
Does fitness prevent altitude sickness?
Not reliably; anyone can get it.
Is oxygen needed?
Emergency oxygen is for rescue, not routine use.
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