| What it is | Illness from ascending too fast |
| Also known as | Acute mountain sickness (AMS) |
| Symptoms | Headache, nausea, fatigue, dizziness |
| Can progress to | HAPE, HACE (life-threatening) |
Altitude sickness, or acute mountain sickness (AMS), is illness caused by ascending to high altitude faster than the body can acclimatize to the reduced oxygen. Symptoms include headache, nausea, fatigue, and dizziness. It can progress to the life-threatening conditions HAPE and HACE, so the response is to stop ascending and, if it worsens, descend.
Recognising it
A headache plus nausea, fatigue, or dizziness above ~2,500 m suggests AMS. Worsening breathlessness or confusion signals progression to HAPE or HACE.
Prevention & response
Ascend slowly to allow acclimatization; if symptoms worsen, descend. This article is educational and not a substitute for professional medical advice.
Frequently asked questions
What are the symptoms of altitude sickness?
Acute mountain sickness usually starts with a headache, plus some of: nausea or loss of appetite, fatigue or weakness, dizziness, and poor sleep. It feels somewhat like a hangover. Worsening confusion, breathlessness at rest, or loss of coordination signal dangerous progression to HACE or HAPE.
At what altitude does altitude sickness start?
AMS most often appears above about 2,500 m (8,000 ft), though susceptible people can feel it lower. Risk rises with higher elevation and faster ascent. Individual susceptibility varies widely and isn't strongly related to fitness.
How do you treat altitude sickness?
Stop ascending and rest to let your body acclimatize; hydrate and treat the headache. If symptoms don't improve or get worse — and always for severe symptoms — descend without delay. Descent is the definitive treatment. Seek medical guidance about medications and oxygen.
Sources
- Acute altitude illness — Wilderness Medical Society
- High-altitude travel — CDC