Altitude sickness is the term used to describe theillnesses that are linked to being at a high altitude and that are caused by a reduction in oxygen availability when up high.

Aneto is located at 3,404 metres above sea level, at which point you only have 67% of the oxygen that you do at sea level. This can lead to some changes in your body that are worth familiarising yourself with.




Sea level (0 m) 100%
Benasque (1138 m) 88%
Refugio de la Renclusa (2140 m) 78%
Portillón Superior (2870 m) 72%
Aneto summit (3404 m) 67%

Oxygen level (%) based on an altitude of 0 metres. (

Does altitude sickness only occur on high mountains?

Altitude sickness is linked to a lack of oxygen in the blood, something that causes a series of symptoms that only get worse as the altitude increases. In the Pyrenees, you won’t reach extreme altitudes (classed as those above 5,550 metres); however, the symptoms resulting from a lack of oxygen can start to be seen above 2,500 metres, and which take the form of acute mountain sickness (AMS).

What are the symptoms?

The most noticeable symptoms are headaches, lack of breath and unusual fatigue. You may also experience nausea, lethargy and insomnia, all of which will impact your decision-making ability.

AMS is related to altitude and the speed at which you ascend. In order to reach the summit of Aneto, you must climb 1,500 metres in just a few hours if you start from La Besurta or Puente de Coronas, and almost 2,300 metres if you leave from Benasque (1,138 m), and this rapid ascent may take its toll on your body.

Mal de Altura en el Aneto

How can I prevent this problem?

A great way is by splitting the ascent up into two days and spending the night at La Renclusa refuge. By starting your trip to Aneto from 2,100 metres above sea level, you will marginally reduce the number of metres you need to climb on the day of the summit, but most importantly, sleeping and spending a while breathing at that altitude will help your body better adapt to the circumstances.

It is also vital that you keep properly hydrated before and during the activity.


Telephone signal Progression and signposts