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EmpyreanTravel · Est. 1984

Health & Safety

Altitude Sickness Guide: Prevention, Symptoms and High Destinations

Altitude sickness guide: who gets it, how to prevent it with a gradual ascent, warning signs that mean descend now, and how high popular destinations are.

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Reviewed · 4 min read

Altitude sickness can affect anyone traveling above about 8,000 feet, regardless of fitness. The best prevention is a gradual ascent: the CDC advises against going from low elevation to above 9,000 feet in a single day, then raising your sleeping elevation by no more than about 1,600 feet a day. Prescription medicine helps some travelers; ask a clinician. Worsening symptoms mean descend.

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Empyrean Travel · Boarding Pass
Risk begins
About 8,000 ft (roughly 2,400 m)
Ascent rule
Above 9,000 ft, sleep ~1,600 ft higher per day at most
First 48 hours
Avoid alcohol and heavy exercise
Emergency signs
Confusion, poor coordination, breathless at rest
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What is altitude sickness, and who gets it?

Acute mountain sickness, the common form, happens when your body hasn’t yet adjusted to lower oxygen levels at elevation. It usually feels like a hangover: headache plus tiredness, nausea, dizziness or poor sleep, typically starting within hours to a day of arriving high.

It can affect anyone, and being fit doesn’t protect you. The biggest factors are how high you go, how fast you get there and how high you sleep. Having had altitude illness before is one of the best predictors that you’ll get it again.

How do you prevent altitude sickness?

Slow ascent is the single most effective prevention. Plan it into the itinerary, not just the packing list.

  • Avoid going from low elevation to above 9,000 feet (2,750 m) in one day when you can, for example by spending a night at an intermediate elevation
  • Above 9,000 feet, raise your sleeping elevation by no more than about 1,600 feet (500 m) per day, and build in rest days
  • Climb higher during the day if you like, but sleep lower
  • Avoid alcohol and heavy exercise for the first 48 hours
  • Ask a clinician whether preventive medicine makes sense for you; prescription options can help some travelers acclimatize

What are the warning signs that it’s becoming an emergency?

Mild symptoms mean rest and don’t go any higher until they resolve. If they get worse despite rest, descend. Never continue upward with symptoms.

Two rarer forms are medical emergencies. Fluid in the brain, called HACE, shows up as confusion, extreme drowsiness or loss of coordination. Fluid in the lungs, called HAPE, causes breathlessness even at rest, weakness and cough. Either one means descending immediately and getting medical care.

Who should talk to a doctor before a high-altitude trip?

Anyone heading above about 8,000 feet benefits from a conversation with a clinician, and it’s essential if you have heart or lung disease, are pregnant, have had altitude illness before, or are traveling with young children or older relatives. A travel-medicine visit can cover altitude alongside vaccines; see our travel health and vaccines guide.

For treks and remote high destinations, check that your insurance includes medical evacuation. Our guide to health insurance abroad explains the gaps to fill.

How do you plan an itinerary around altitude?

Build the ascent into the route. In Peru, many itineraries start in the lower Sacred Valley before Cusco. On Kilimanjaro, longer routes with more days on the mountain give your body more time to adjust and generally improve summit success. Arriving in Colorado ski country from sea level, a night in Denver first can help.

Pack for the conditions too: high-altitude sun and cold are intense. Our adventure trek packing list covers layers, sun protection and a basic medical kit.

How high are popular destinations?

  • Cusco

    Peru · about 11,150 ft (3,400 m)

    The gateway to Machu Picchu, which itself sits lower, at about 7,970 ft (2,430 m). Starting in the Sacred Valley eases the climb.

  • La Paz

    Bolivia · about 11,900 ft (3,640 m)

    Its airport, in neighboring El Alto, sits above 13,000 ft, so you feel the altitude the moment you land.

  • Quito

    Ecuador · about 9,350 ft (2,850 m)

    A common stop before Galápagos cruises; the islands themselves are at sea level.

  • Lhasa

    Tibet · about 11,975 ft (3,650 m)

    One of the highest cities travelers commonly fly into directly, so take the first days slowly.

  • Mount Kilimanjaro

    Tanzania · 19,341 ft (5,895 m)

    Africa’s highest peak. Choose a longer route for better acclimatization.

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  • Colorado ski towns

    USA · Breckenridge about 9,600 ft (2,900 m)

    Altitude headaches are common on day one, especially after a morning flight from sea level.

Frequently asked questions

At what altitude does altitude sickness start?

Risk generally begins around 8,000 feet, roughly 2,400 meters, according to the CDC, and rises the higher and faster you go. Some sensitive travelers notice mild symptoms a little lower. Sleeping elevation matters more than the highest point you reach during the day, which is why itineraries are built around where you spend each night.

Does being fit prevent altitude sickness?

No. Fitness doesn’t protect you from altitude sickness, and very fit travelers sometimes push too hard, too fast. Your speed of ascent, the elevation where you sleep and your individual susceptibility matter far more. Fitness does make trekking more enjoyable, but it’s the gradual ascent and rest days that help your body adjust.

Is there medicine for altitude sickness?

Yes. Prescription medicines can help prevent acute mountain sickness and speed acclimatization for some travelers, and over-the-counter pain relievers may ease headaches. Whether medicine is right for you depends on your health, other medications and itinerary, so talk to a clinician before you go. Medicine supports a gradual ascent; it doesn’t replace one.

How long does it take to acclimatize to high altitude?

Most people adjust to a given elevation over one to several days, and symptoms of mild altitude sickness often ease within that time if you don’t go higher. Each further climb requires more adjustment, which is why multi-day treks add rest days. Plan a relaxed first day or two at any high destination rather than a packed schedule.

Can you get altitude sickness at a ski resort?

Yes. Many Colorado ski towns sit around 9,000 feet or higher, with summits well above that, and visitors arriving from sea level commonly feel headaches, poor sleep or fatigue on the first day or two. Drink water, go easy on alcohol, ski gently on day one and consider a night at a lower elevation on the way in.

Official sources

Rules, fees and schedules change — confirm the latest details at the source before you travel.

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