Altitude Sickness: Common Questions
Illness caused by ascending faster than the body can adapt to reduced oxygen.
Last revised
Altitude Sickness: the questions people actually ask, answered from published guidance.
Key takeaways
- Usually starts above: 2,500 metres
- Early symptoms: headache, nausea, fatigue, poor sleep
- Most useful single change: Ascend gradually and build in acclimatisation days.
- Commonest mistake: Ascending further with any symptoms.
- See a doctor if any of the signs under "When to get help" below apply to you.
What is Altitude Sickness?
Illness caused by ascending faster than the body can adapt to reduced oxygen.
Why does it matter?
It affects fit and unfit people alike, and the severe forms are rapidly fatal if you keep ascending.
Usually starts above for Altitude Sickness?
2,500 metres.
Early symptoms for Altitude Sickness?
Headache, nausea, fatigue, poor sleep.
Golden rule for Altitude Sickness?
Do not ascend further with symptoms.
HACE and HAPE for Altitude Sickness?
High altitude cerebral and pulmonary oedema; emergencies.
What is the single most useful thing to do?
Ascend gradually and build in acclimatisation days.
What is the most common mistake?
Ascending further with any symptoms.
When should I see a doctor?
Descend immediately and seek emergency help for confusion, unsteadiness, inability to walk in a straight line, severe headache not relieved by painkillers, breathlessness at rest, or coughing frothy or pink sputum — these indicate cerebral or pulmonary oedema and are rapidly fatal. Descent is the treatment; do not wait.
Where to go next
- Popular Beliefs About Altitude Sickness, and What Is Actually Published
- New to Altitude Sickness? Start Here
- Altitude Sickness — the reference entry
- Returning Traveller Illness: What Published Guidance Supports
- Travel Vaccinations: What the Evidence Actually Says
When to get help
Descend immediately and seek emergency help for confusion, unsteadiness, inability to walk in a straight line, severe headache not relieved by painkillers, breathlessness at rest, or coughing frothy or pink sputum — these indicate cerebral or pulmonary oedema and are rapidly fatal. Descent is the treatment; do not wait.
Where this comes from
How this page was put together
Every figure, recommendation and warning above is taken from the guidance named in Where this comes from. Nothing on this page is inferred, summarised or generalised beyond what those bodies publish: where they give a number, it is their number, and where they are silent, so are we. Pages are rebuilt whenever the underlying record changes. Sign-off by a named clinician, where it has happened, is shown at the top of the page along with the date.
Medical disclaimer
This article is general information, not medical advice. It cannot account for your own history, medication or circumstances. Always speak to a GP, pharmacist or another qualified health professional before making changes that affect your treatment, and never delay seeking medical advice because of something you have read here. In an emergency, call 999.
