Altitude Sickness on Holiday in 2026: It Hits Tourists in High Cities and Sights, Not Just Trekkers

Altitude sickness is filed in most people's minds under "mountaineering" — something that happens to climbers gasping near the summit of Everest. In 2026, that mental picture is quietly costing ordinary holidaymakers a ruined trip and, occasionally, a hospital bed. You do not have to climb anything to get it. You only have to go up, and plenty of the world's most photographed holidays go up a long way.

Cusco, the gateway to Machu Picchu, sits at around 3,400m. La Paz in Bolivia is near 3,600m. Lhasa, in Tibet, is around 3,650m. Quito, several Colorado ski towns, and yes, the classic Himalayan teahouse trek — all put visitors well above the altitude where the body starts to struggle for oxygen. People fly in, drop their bags, and head straight out sightseeing. That is exactly the wrong move.

What acute mountain sickness actually feels like

The common form is called acute mountain sickness, or AMS. It usually appears within 6 to 24 hours of arriving at altitude and, unhelpfully, feels a lot like a bad hangover: a throbbing headache, nausea or loss of appetite, dizziness, tiredness and broken, restless sleep. Many travellers blame the long flight, the airline food or a night of celebratory drinks, and simply push on. That delay is where trouble starts.

At around 2,500m a meaningful share of visitors feel some effect; by roughly 3,000m the proportion climbs higher still. It is not rare, and it is not a sign of weakness. Crucially, fitness and age are poor predictors. A marathon runner in their twenties can be flattened while their unathletic grandparent feels fine — the body's response to thin air is largely down to genetics and how fast you went up, not how many press-ups you can do.

The golden rules that keep it mild

Prevention is mostly common sense applied with discipline. Ascend gradually and give your body time to adjust. Once high, "climb high, sleep low" — you can visit a higher viewpoint by day, but sleep at a lower elevation. Above about 3,000m, keep the height you sleep at rising slowly rather than in big jumps. Do not over-exert on your first day at a new altitude; take it gently. Drink plenty of water, and go easy on alcohol, which makes everything worse. And listen to symptoms rather than powering through them.

If mild symptoms appear, the rule is simple: do not go any higher until they have settled. If they get worse despite resting, descend. Even a few hundred metres down can turn things around, and most people recover within a day or two once they stop climbing.

HACE (high-altitude cerebral edema, fluid affecting the brain) and HAPE (high-altitude pulmonary edema, fluid in the lungs) are the dangerous end of the spectrum. They are uncommon, but they can develop from ignored AMS and they can be fatal. The warning signs are a change in how someone thinks or moves, or breathlessness when they are simply sitting still.

There is a prescription medicine, acetazolamide (often sold as Diamox), that a doctor may recommend to help prevent or ease altitude sickness for some travellers. It is not a licence to ascend faster and it does not replace good acclimatisation — talk to a doctor or travel clinic before your trip about whether it is right for you. For a fuller walkthrough of symptoms and prevention, see our complete guide to altitude sickness in Nepal and our rundown of the simple rules that keep Everest trekkers safe.

Why Nepal takes this seriously

This is not an abstract topic for us. Nepal's classic treks routinely cross 3,000m to 5,500m — Everest Base Camp reaches 5,364m and the Annapurna Circuit tops out on the Thorong La at 5,416m. That is precisely the altitude band where this bites hardest, which is why a properly built Himalayan itinerary is not just a list of villages. It has acclimatisation days deliberately baked in, a "climb high, sleep low" rhythm, and a licensed guide who watches every member of the group for early symptoms and is willing to turn someone around.

The honest advice we give every client is the unglamorous one: never trade away an acclimatisation day to save time or money, and tell your guide the moment you feel off. A headache mentioned early is a rest day; a headache hidden for pride can become an evacuation. If you are planning a high trek and want an itinerary that respects your body, talk to us about a properly paced route — the extra day is always cheaper than a helicopter.

This article is general information, not medical advice. Altitude illness can be serious. Speak to a doctor or a travel clinic before a high-altitude trip, and seek medical help if symptoms develop.

Cover photo: Irene Constantino via Pexels (Pexels License).