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Travel health

How to Prevent Altitude Sickness

The most effective way to prevent altitude sickness is gradual ascent, which gives your body time to adapt to lower oxygen levels. Staying hydrated, sleeping lower than your daytime high point, avoiding alcohol for the first 48 hours, and adding rest days also help. Preventive prescription medication can reduce risk for rapid ascents.

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What is altitude sickness?

As you go higher, the air contains the same percentage of oxygen but at lower pressure — each breath delivers less oxygen to your blood. Altitude sickness (the medical umbrella term is Acute Mountain Sickness, or AMS) is your body's response to this relative oxygen shortage 1. It typically begins above roughly 8,000 feet (2,500 meters) and becomes more common and severe above 11,000 to 12,000 feet (about 3,300 to 3,700 meters).

Symptoms of mild AMS include headache (the hallmark), fatigue, dizziness, loss of appetite, and nausea. These usually appear within a few hours of arriving at altitude and often improve with a day of rest — if you do not go higher.

More serious forms — High Altitude Pulmonary Edema (HAPE, fluid in the lungs) and High Altitude Cerebral Edema (HACE, swelling in the brain) — are uncommon but life-threatening 12. Recognizing the difference and knowing when to descend is as important as prevention.

Fitness level does not protect you from altitude sickness. Very fit athletes get it; sedentary travelers sometimes do not. Individual susceptibility is not fully predictable.

How do you ascend safely?

Gradual ascent is the foundation of prevention 12. General principles used in wilderness medicine include:

  • Do not ascend too fast. Above 8,000 feet, avoid increasing your sleeping elevation by more than about 1,000 to 1,500 feet per night.
  • Climb high, sleep low. If you reach a higher elevation during the day, descend to a lower camp or altitude to sleep. Sleep altitude matters more than the peak you reach during the day.
  • Rest days. Build in a day of acclimatization without gaining elevation for every 2,000 to 3,000 feet gained above 8,000 feet.
  • Listen to your body. Headache alone is a signal. If it is more than mild, do not go higher until it resolves.

What other prevention strategies help?

Hydration. Stay well hydrated at altitude — dry mountain air increases fluid loss through breathing. Urine should be pale, not dark. Avoid alcohol for the first 48 hours; it impairs the body's acclimatization response and disrupts sleep 1.

Sleep. Sleep architecture is often disrupted at altitude, with episodes of periodic breathing. This is normal but can worsen fatigue. Sleeping lower helps.

Prescription medication. Acetazolamide is the most well-studied medication for AMS prevention and is recommended by the Wilderness Medical Society as the primary pharmacologic option for rapid ascent or high-risk travelers 2. It works by increasing the breathing rate, which helps the body take in more oxygen. It is typically started one to two days before ascent and continued for two days after reaching your highest planned altitude. People with sulfa allergies should mention this to their clinician. A prescription is required.

Avoid sedatives. Sleeping pills and alcohol can suppress the breathing drive at altitude and worsen oxygen levels during sleep 12.

Rapid ascent by vehicle or plane. Driving or flying directly to a high-altitude destination (such as landing in Cusco, Peru, or driving to a high-altitude ski resort) leaves no time for gradual acclimatization. This is when preventive medication is most often considered.

When should someone with health conditions get evaluated before a high-altitude trip?

People with heart or lung conditions — including heart failure, coronary artery disease, pulmonary hypertension, and COPD — face significantly higher risk of serious altitude illness and should see their cardiologist or pulmonologist before any high-altitude travel 1. People with prior altitude sickness are more likely to get it again, and their clinician may recommend preventive medication and a conservative ascent plan 2.

Pregnancy and high altitude require a discussion with your OB — sustained high altitude can affect fetal oxygen supply, and common preventive medications may not be appropriate.

A brief primary care or travel medicine visit before a major high-altitude trip is worthwhile for any traveler who is uncertain about their plan.

Common questions

Can fit, healthy people get altitude sickness?

Yes. Fitness level does not protect against altitude sickness. Physical conditioning improves performance at altitude but does not prevent the physiologic effects of reduced oxygen pressure. Very fit athletes get AMS; sedentary travelers sometimes do not.

What altitude does altitude sickness start?

Symptoms typically start above roughly 8,000 feet (2,500 meters) and become more common and severe above about 11,000 to 12,000 feet (3,300 to 3,700 meters). Individual thresholds vary.

Does acetazolamide (Diamox) prevent altitude sickness?

Acetazolamide can meaningfully reduce the risk of AMS and is the primary medication recommended by the Wilderness Medical Society for high-risk ascents. It requires a prescription, should be started one to two days before ascent, and is continued for two days after reaching peak altitude. Discuss with your clinician whether it is appropriate for your trip and health history.

What are the warning signs of serious altitude illness?

The hallmark of dangerous progression is continued symptoms at rest, especially worsening headache that does not improve, confusion or difficulty walking straight (signs of HACE), or cough with pink frothy sputum, severe shortness of breath at rest, or crackling sounds with breathing (signs of HAPE). If any of these occur, descend immediately — do not sleep at the same altitude.

Should I drink more water at altitude?

Staying well-hydrated is advisable at altitude because dry mountain air increases fluid loss through breathing. Aim for pale urine. That said, hydration alone will not prevent AMS — gradual ascent remains the most effective strategy.

Talk to a clinician

Nina Osei, NP — Nurse Practitioner

checkups, refills & skin. Gale can match you with a licensed clinician for a visit.

Find care →

Emergency signs at altitude — descend immediately

  • —Loss of coordination or difficulty walking in a straight line — descend and seek emergency care
  • —Confusion, unusual behavior, or difficulty speaking at altitude
  • —Severe shortness of breath at rest, especially with cough
  • —Coughing up pink or frothy mucus
  • —Extreme fatigue or inability to stand
  • —Severe or worsening headache not relieved by rest and over-the-counter pain relief

Signs of HACE (confusion, loss of coordination) or HAPE (severe breathlessness at rest, frothy cough) are life-threatening. Begin descent immediately — every foot lower helps — and call for emergency rescue if available. In remote areas, a portable hyperbaric chamber can be used while awaiting evacuation.

This article provides general educational information about altitude sickness prevention. It is not a substitute for personalized advice from a licensed clinician or travel medicine specialist. Anyone with heart or lung conditions, prior altitude illness, or a pregnancy should consult a provider before high-altitude travel.

References

  1. 1.Centers for Disease Control and Prevention (2025). High-Elevation Travel and Altitude Illness — CDC Yellow Book 2026. CDC Yellow Book. link ✓AMS definition, onset altitude, symptoms, HAPE and HACE recognition, gradual ascent principles, acetazolamide use, alcohol and sedative avoidance, cardiac/pulmonary and pregnancy special populations
  2. 2.Luks AM, Beidleman BA, Freer L, Grissom CK, Keyes LE, McIntosh SE, Rodway GW, Schoene RB, Zafren K, Hackett PH (2024). Wilderness Medical Society Clinical Practice Guidelines for the Prevention, Diagnosis, and Treatment of Acute Altitude Illness: 2024 Update. Wilderness & Environmental Medicine. doi:10.1016/j.wem.2023.05.013 ✓Evidence-based recommendations for gradual ascent, acetazolamide as primary pharmacologic prevention, HAPE and HACE criteria, avoiding sedatives at altitude, and recommendations for prior AMS sufferers

2 sources, numbered by first appearance. General health information, not medical advice — synthetic demonstration content.