Acute mountain sickness can start appearing at around 2,500 meters, and it doesn't depend on how physically fit you are — it can happen to anyone, even someone who has climbed that same mountain before without any issue.
Typical symptoms include headache, nausea, unusual fatigue and dizziness. On our outings to Sollipulli and Antuco, where we go above that altitude, guides actively monitor how everyone in the group is feeling, not just whoever looks the most tired.
The most effective prevention is gradual ascent and staying consistently hydrated — avoid alcohol the night before a high-altitude outing. If symptoms appear, the rule is simple and non-negotiable: don't keep ascending with symptoms, and descend if they get worse. No summit view is worth it if your body is telling you otherwise.
This is one of the reasons volcano outings always go out with a guide — recognizing these signs in time in someone else is harder than recognizing them in yourself.
