Every photographer who comes to the Andes with me arrives at altitude before they have done anything to earn it. They step off an airplane at 3,400 m/11,150 ft in Cusco, or 4,061 m/13,320 ft on the El Alto rim above La Paz, having been at sea level that morning. There is no walking-in period, no gradual approach march. The mountain starts at the airport door.
That single fact shapes every itinerary I design. Acclimatization is not something I add to a trip as a safety feature. It is the structure the trip is built on, and once you understand what your body is doing during those first days, the shape of our routes stops looking arbitrary and starts looking obvious.
This post is about that process. If you want the symptoms and what to do about them, I wrote about altitude sickness separately.
What acclimatization actually is
The air at 3,600 m/11,800 ft has the same percentage of oxygen as the air at the beach. What it does not have is pressure. Roughly a third fewer molecules arrive in your lungs with each breath, and your body has to make up the shortfall. It does that in stages, and the stages run on very different clocks.
Within minutes, you breathe more. This is the fastest response and the most important one. Sensors in your neck detect the drop in blood oxygen and your breathing rate and depth increase, at rest as well as during exertion. Most people never notice it happening. It is why you feel short of breath climbing one flight of stairs in La Paz on your first evening.
Within hours to days, your blood chemistry shifts. Breathing harder blows off carbon dioxide, which makes your blood more alkaline, which in turn tells your body to breathe less. Those two signals fight each other for the first day or two. Your kidneys settle the argument by dumping bicarbonate, which lets the breathing response run properly. This is also why you urinate more at altitude, and it is a good sign rather than a worrying one. Plasma volume drops at the same time, which concentrates the red cells you already have.
Within days to weeks, you make more red cells. This is the one everybody has heard of, and it is the slowest. Meaningful increases take one to two weeks and continue for months. On a two-week photo tour you get the beginning of it, not the whole thing. Anyone who tells you they acclimatized in three days is describing the breathing response, not the blood.
There is also a limit. Above roughly 5,000 m/16,400 ft, nobody truly adapts. You deteriorate more slowly if you are acclimatized, but you still deteriorate. Permanent human settlement stops at around 5,100 m/16,700 ft for a reason. This is one of several reasons our photography itineraries keep their sleeping elevations well below that line.
The number that matters is where you sleep
This is the single most useful thing I can teach you, and most people get it backwards.
Your sleeping elevation drives altitude illness. The highest point you reach during the day matters much less. You can stand on a 4,700 m/15,420 ft pass for an hour, photograph it, and drive back down to sleep at 3,800 m/12,470 ft, and your body treats that as a 3,800 m night. Breathing slows and becomes irregular during sleep, blood oxygen drops to its lowest point of the twenty-four hours, and that long low stretch is where the trouble starts.
Guides have a phrase for using this deliberately: climb high, sleep low. It is not folklore. It is the mechanism, and it is the reason our days can be more ambitious than our nights.
The published rule, and what it means for a real itinerary
The Wilderness Medical Society publishes the guidance most operators work from, updated in 2024. Above 3,000 m/9,840 ft, it advises not increasing your sleeping elevation by more than 500 m/1,640 ft in a day, and taking a rest day, meaning no gain in sleeping elevation at all, every three to four days.
The part of that guidance that rarely gets quoted is the part that matters most in the Andes. The panel acknowledges that terrain and logistics often make a strict 500 m per night impossible, and says that in those cases the trip should be judged on its average: total elevation gain divided by the number of ascent days, kept under the same threshold, with acclimatization days built in around the big jumps.
That averaging provision is the whole design problem, and it is where an operator either does the work or does not.
What the difference in pacing is actually worth
It is easy to say slow is better. The published figures put a number on it, and the spread is not subtle.
Reaching 4,000 to 5,000 m/13,120 to 16,400 ft over three days or more puts the rate of fluid in the lungs under 0.2 percent. Reaching the same elevation in a single day pushes it to around 7 percent. At 5,500 m/18,040 ft, people who trekked in over four to six days run about 2.5 percent. People who arrived by air at the same elevation run about 15.5 percent.
Same mountains, same people, same altitude. Only the pace changed, and the risk moved by a factor of ten or more. Gaining more than 600 m/1,970 ft of sleeping elevation per day sits at around 4 percent on its own.
Rate of ascent is not one variable among many. It is the dominant one, and it happens to be the one an operator controls completely. That is why I will argue with a client about an itinerary before I will argue about a lens.
A worked example: Bolivia, night by night
Bolivia is the hardest arrival of the six countries I work in, and the clearest illustration of the method, so it is worth showing rather than describing.
You land on the El Alto rim at 4,061 m/13,320 ft. That is higher than most people have ever slept. We do not let you sleep there. We take you straight down into La Paz and put you at 3,100 m/10,170 ft, the lowest point of the city. La Paz spans roughly 900 m of vertical from its lowest neighborhoods to its highest, which no other city in the world does, and that vertical range is a tool I use on night one.
Sleeping elevation night by night on a Bolivia photography itinerary, showing the arrival descent from El Alto into La Paz.
The arrival descent. A drop of roughly 1,000 m on the first night, then two flat nights in La Paz with no gain at all. Your breathing response gets a day and a half of head start before anything is asked of it.
The plateaus. Two nights at Lake Titicaca at 3,812 m/12,510 ft, then two or three at the Salar de Uyuni at 3,600 m/11,810 ft, which is slightly lower. Those flat stretches are where the adapting actually happens. They look like slow days on a calendar. They are the reason the second week works.
The ceiling comes last. Laguna Colorada in the Sud Lipez at 4,200 m/13,780 ft, then Sajama at 4,330 m/14,210 ft, both in the second week rather than the first.
Net gain in sleeping elevation across that itinerary is about 1,230 m over roughly nine nights. Averaged out, that is a little over 130 m per night, against a published threshold of 500 m. The ceiling stays at 4,330 m rather than the 5,000 m and above where the severe forms become meaningfully more common.
None of that is accidental, and none of it costs you photographs. Chacaltaya at 5,395 m/17,700 ft and the Sud Lipez lagoons are places we drive to rather than climb to, so the daytime highs run well above anywhere anybody sleeps.
The same rule, six different problems
Every country in the Andes presents the same physiology and a different logistical puzzle.
In Peru, Cusco at 3,400 m/11,150 ft is the arrival, not the base. We take people down into the Sacred Valley at around 2,800 m/9,190 ft for the first nights, then back up to Cusco and higher once the body has caught up. For Cordillera Blanca and Huayhuash work the platform is Huaraz at 3,052 m/10,010 ft, used as a fixed base with day exposures to Llanganuco at 3,850 m/12,630 ft and Portachuelo at 4,767 m/15,640 ft before any trek begins. Classic climb high, sleep low, over a week.
In Chile, San Pedro de Atacama at 2,408 m/7,900 ft lets us do something unusual: you never change rooms. Day trips run to the Puritama springs at 3,475 m/11,400 ft, the Miscanti and Miniques lagoons above 4,100 m/13,450 ft, and El Tatio at 4,300 m/14,110 ft, with the same bed every night. Repeated high exposure, one sleeping elevation.
Colombia and Ecuador are gentler and run on a different rhythm, with lower bases and daily up-and-down movement. Argentina does most of the work by road, which lets us control the profile almost hour by hour. The detail for all six is on our high altitude information page.
What you can do before you arrive
Arrive early if your schedule allows it. A night or two at moderate elevation before the trip starts is the single most effective thing within your control, and the published guidance supports it. Even one night at an intermediate elevation measurably lowers risk.
Talk to your own physician about acetazolamide, sold as Diamox, well before you travel rather than the week you leave. It has a genuine and well-established role, and it is not right for everyone, particularly anyone with a history of severe reaction to sulfa drugs. That assessment is your physician’s to make, not mine.
Sleep properly in the days beforehand, arrive in decent health, and if you have had altitude illness before, tell me. A previous episode is one of the better predictors we have.
And take the first day seriously. The most common mistake I see is a photographer who feels fine on arrival afternoon and goes for a walk up a hill. The breathing response has not finished adjusting yet. You are not proving anything, and you can spend the next two days paying for it.
What does not work
Fitness does not protect you. Trained runners get altitude illness at the same rate as everyone else. What fitness decides is how much of the trip you enjoy, which is a real benefit and a different one. Our challenge levels page goes into what each tour physically asks of you.
Coca tea does not prevent or treat altitude illness. It is part of daily life across the Andes, you are welcome to enjoy it, and it will do nothing for your acclimatization. Be aware it can leave traces in a workplace drug test.
Brief exposure to thin air beforehand, the hypoxic-tent-for-an-hour approach, appears to do little. The research suggests useful preacclimatization needs long daily exposures over a week or more, not short sessions. If you have the time and equipment for that, it is real. Most people do not.
And pushing through does not work. Going higher on a body that is already telling you it has not caught up is the one decision that turns a mild first night into an evacuation.
Why any of this matters to a photographer
I could make all of this sound like a medical lecture, but the reason I care about it is simpler. Acclimatization done properly is invisible. You are not counting your breaths at the Salar at dawn or wondering whether the headache means something. You are working the light, because your body stopped being the subject of the trip somewhere around day three or four.
Done badly, it is the only thing you remember. I have watched people lose the best two days of a two-week trip because somebody wanted to save a night on the front end. Not a good strategy no matter how you work the numbers. Time to acclimatize is a requirement, not an option.
The nights you spend not gaining elevation are the ones that buy you the rest of the trip. That is the whole argument, and it is why our itineraries look the way they do.
The full reference, including what we carry in the field, what we watch for and how the rescue picture differs by country, is on our high altitude information page.
Please get in touch if you have any questions about seasons, lodges, tour design and private guiding.
— Sergio Ballivián, forty years photographing the wild places of South America
