| What it is | The body adapting to altitude |
| How | Faster breathing, more red blood cells |
| Rule of thumb | 'Climb high, sleep low' |
| Prevents | Altitude sickness |
Acclimatization is the physiological process by which the body gradually adjusts to the lower oxygen of high altitude — by breathing faster, producing more red blood cells, and other adaptations. Ascending slowly to allow acclimatization is the key to preventing altitude sickness; the body typically needs days to adapt to each major elevation gain.
How it works
Faster, deeper breathing and, over days, more oxygen-carrying red blood cells let you function in thin air.
How to acclimatize
Ascend gradually, build in rest days, and follow ‘climb high, sleep low’ to prevent altitude sickness and its severe forms, HAPE and HACE.
This article is educational and not a substitute for professional medical advice.
Frequently asked questions
What is acclimatization?
Acclimatization is the set of changes your body makes to cope with the lower oxygen at altitude — breathing faster and deeper, the heart working harder, and over days producing more oxygen-carrying red blood cells. Allowing time for these adaptations is how climbers avoid altitude sickness.
How long does acclimatization take?
Initial adjustments begin within hours to a couple of days, while fuller adaptation like increased red blood cells takes one to several weeks. A common guideline high up is to increase your sleeping elevation by no more than about 300-500 m per night, with rest days built in.
What does 'climb high, sleep low' mean?
It's a key acclimatization strategy: ascend to a higher elevation during the day to stimulate adaptation, then descend to sleep at a lower one. Sleeping lower than your daytime high point helps the body acclimatize while reducing the risk of altitude illness overnight.
Sources
- Altitude illness prevention — Wilderness Medical Society
- Going to high altitude — UIAA Medical Commission