Altitude sickness (acute mountain sickness) is the single biggest factor when we design a trekking or expedition itinerary. It’s not caution for caution’s sake: more than anything else, it decides whether someone reaches their goal safe and sound. And it can hit anyone. It doesn’t matter how fit you are: a twenty-five-year-old fresh out of the gym can get it just as badly as someone less trained. It comes down to how your body handles a lack of oxygen, not how much you can lift.
From around 2,500-3,000 meters you already feel it. Up there you’re breathing somewhere between 25% and 30% less oxygen than at sea level, because air pressure drops with altitude and every breath brings in less of it. And the risk keeps climbing with every night you sleep higher. That’s why acclimatization isn’t an add-on to the itinerary. It is the itinerary.
The first warning signs are headache, odd fatigue, dizziness, nausea, trouble sleeping. They feel a lot like a hangover and usually show up 2 to 12 hours after you arrive at altitude. Any one of them on its own doesn’t mean much, but a few together do: your body is telling you it isn’t keeping up with how fast you’re climbing. And here’s the part that matters most: if you’re not feeling right, you tell your guide then and there. Don’t wait until the end of the day.
If it’s ignored and the climb keeps going, things can get serious fast. High Altitude Cerebral Edema (HACE) shows up as confusion, losing your coordination while walking, acting like you’ve had too much to drink, and it can reach a coma in under 24 hours. High Altitude Pulmonary Edema (HAPE) starts with a cough and a fatigue that’s out of proportion to the effort, and can end with breathlessness even at rest. Both are real medical emergencies, and in both cases the first move is the same: go down. The sooner, the better.
Real prevention has nothing to do with miracle pills. It’s about the pace you climb at. Above 3,000 m, the usual guidance is to gain no more than 500 m of sleeping altitude a night, and add an extra acclimatization day for every extra 1,000 m you climb to sleep. Drinking plenty of water, skipping alcohol for the first 48 hours, and eating well all help, but none of it replaces the time your body needs.
And Diamox (acetazolamide), which you’ve probably heard of: there are studies showing it can help speed up acclimatization and lower risk in some cases. We don’t take a position on it or prescribe it, that’s a conversation to have with your own doctor before you travel, based on your specific case. Whether you take it or not, what’s non-negotiable is an itinerary with enough acclimatization built in. The pill can help, but it doesn’t replace the days your body needs.
At Thin Air we build itineraries with the acclimatization they actually need, full stop. Safety comes first, always, even if that means one more day on the trip or a bit more cost. It’s a real problem in this industry: there are agencies out there that aren’t specialized in high-altitude mountaineering and cut acclimatization days to sell a shorter or cheaper package, then cover that gap with medication instead of time. That’s playing with people’s safety, and we don’t do that.
Our guides are officially licensed and know how to spot symptoms in time, and if someone needs to come down, they come down, no drama but no hesitation either. We carry a medical kit and, depending on the destination, a satellite phone, so we can act fast if something goes wrong.
See our high-altitude destinations: Campo Base del Everest · Aconcagua · Kilimanjaro · el Monte Kenia