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Altitude Sickness: Symptoms, Treatment, and When to Get Help

Altitude sickness occurs when the body cannot adapt to lower oxygen levels at high elevation. Mild symptoms — headache, fatigue, nausea — typically begin within hours above roughly 8,000 feet and improve with rest at the same altitude. Stop ascending when symptoms appear; descend immediately if they worsen. HAPE and HACE are life-threatening emergencies requiring immediate descent.

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What actually happens at altitude?

At high elevation, the air contains the same fraction of oxygen as at sea level, but lower atmospheric pressure means each breath delivers less oxygen to your lungs. Your body gradually adjusts — breathing faster, producing more red blood cells — but this acclimatization takes days 1. If you ascend faster than your body can adapt, you develop altitude sickness, medically called Acute Mountain Sickness (AMS). Almost anyone can get it regardless of age or fitness level; prior trips to altitude do not guarantee immunity on a subsequent ascent 2.

What does mild altitude sickness feel like?

Mild AMS typically begins within 6–12 hours of reaching altitude and often feels like a hangover: dull headache, fatigue, loss of appetite, mild nausea, and poor sleep 1. The Lake Louise Scoring System — a standardized clinical tool — defines AMS as a headache plus at least one of gastrointestinal discomfort, fatigue, dizziness, or difficulty sleeping in the setting of a recent altitude gain 2.

These symptoms are not immediately dangerous, but they are your body's signal to stop climbing. Rest at the same altitude, drink plenty of water, avoid alcohol, and do not ascend further until symptoms fully resolve — usually within 24 to 48 hours.

What are HAPE and HACE — the dangerous forms?

Two dangerous complications can develop when someone continues ascending while symptomatic 12.

High Altitude Pulmonary Edema (HAPE) involves fluid accumulating in the lungs. Symptoms: breathlessness at rest, a dry or wet cough, extreme fatigue, and a blue tint to the lips or fingertips.

High Altitude Cerebral Edema (HACE) involves brain swelling. Symptoms: severe headache, confusion, stumbling gait, or loss of consciousness.

Both are medical emergencies. The treatment is immediate descent of at least 300–600 meters (roughly 1,000–2,000 feet) — more if possible. Supplemental oxygen helps if available. Do not wait for symptoms to worsen.

How can you prevent altitude sickness?

The most reliable prevention is gradual ascent: gain no more than about 300–500 meters (roughly 1,000 feet) per day once above 2,500 meters (8,200 feet), and build in acclimatization days 12. "Climb high, sleep low" is a well-established mountaineering principle — hike to a higher elevation during the day but return to a lower camp to sleep. Stay well hydrated and avoid alcohol in the first days at altitude.

Acetazolamide (Diamox) is a prescription medication that can reduce AMS risk by stimulating faster, deeper breathing at altitude 2. A systematic review found acetazolamide prophylaxis is associated with roughly a 48% relative-risk reduction for AMS compared to placebo 3. It is not appropriate for everyone — a pre-travel clinician visit is the right place to discuss whether it fits your itinerary and health history.

Who should see a clinician before a high-altitude trip?

A pre-travel clinician visit is worthwhile if you are planning to travel above 8,000 feet — destinations such as Cusco, Peru (11,000 feet), or any mountaineering itinerary. It is especially important if you have heart or lung conditions, are pregnant, or have had altitude sickness before.

A clinician can discuss preventive medication options, help you plan a safe ascent schedule, and advise on whether supplemental oxygen or emergency medications are appropriate for your destination. Physical fitness does not protect against altitude sickness — highly trained athletes are just as susceptible as sedentary individuals 1.

Common questions

Can I fly to a high-altitude city and be fine without acclimatizing?

Many people fly directly to cities like Cusco (11,000 feet) or La Paz (11,900 feet) and experience mild symptoms. Most recover within 24 to 48 hours with rest and hydration. However, a meaningful proportion feel significantly unwell, and a small number develop serious complications. If you have heart or lung conditions, a gradual ascent or a pre-travel clinician visit is strongly recommended.

Is descending really the treatment — even in the middle of the night?

Yes. For HAPE or HACE, immediate descent is the treatment, regardless of time of day or weather conditions. Even a descent of 1,000 to 2,000 feet can be life-saving. Do not wait until morning.

Does drinking a lot of water prevent altitude sickness?

Good hydration helps your body function better at altitude and may reduce symptom severity, but it does not prevent AMS. The single most effective prevention is ascending slowly — no more than roughly 1,000 feet per day above 8,000 feet.

Can children get altitude sickness?

Yes. Children are susceptible to AMS just as adults are, and they may have more difficulty describing their symptoms. Behavioral changes, irritability, and loss of appetite in a child at altitude should be treated as possible AMS. A pediatrician should advise before traveling with young children to high altitudes.

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 →

When altitude sickness becomes an emergency

  • —Difficulty walking a straight line, stumbling, or loss of coordination — this is a medical emergency
  • —Confusion, disorientation, unusual behavior, or difficulty staying awake
  • —Shortness of breath at rest — not just with exertion
  • —A wet, gurgling cough or pink frothy sputum
  • —Severe or worsening headache that does not respond to rest or pain relievers
  • —Inability to keep fluids down
  • —Chest tightness or pressure at rest
  • —Symptoms that are getting worse despite staying at the same altitude

Loss of coordination, confusion, shortness of breath at rest, or a gurgling cough are signs of HACE or HAPE — both life-threatening. Descend immediately, even in the dark. Call 911 or local emergency services, or activate an emergency beacon if in a remote area. Do not wait to see if it improves.

This article provides general health education only and is not a personalized medical evaluation or treatment plan. Altitude sickness can escalate to a life-threatening emergency. Consult a licensed clinician before traveling to high altitude, especially if you have any underlying health conditions.

References

  1. 1.Centers for Disease Control and Prevention (2023). High Elevation Travel and Altitude Illness — CDC Yellow Book 2024. CDC Travelers' Health. link ✓Core epidemiology and clinical management of AMS, HAPE, and HACE; the 1,000 feet per day ascent guideline; preventive pharmacotherapy including acetazolamide
  2. 2.Luks AM, Auerbach PS, Freer L, et al. (2019). Wilderness Medical Society Clinical Practice Guidelines for the Prevention and Treatment of Acute Altitude Illness: 2019 Update. Wilderness & Environmental Medicine. doi:10.1016/j.wem.2019.04.006 ✓Evidence-based graded recommendations for AMS prevention and treatment including ascent rate, the Lake Louise Score diagnostic criteria, HAPE/HACE management, and acetazolamide use
  3. 3.Ritchie ND, Baggott AV, Todd WTA (2012). Acetazolamide for the prevention of acute mountain sickness: a systematic review and meta-analysis. Journal of Travel Medicine. doi:10.1111/j.1708-8305.2012.00629.x ✓Acetazolamide prophylaxis associated with approximately 48% relative-risk reduction for AMS compared with placebo; 250 mg/day as effective as higher doses

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