Altitude Sickness: Symptoms, Prevention & Treatment for Travelers

Altitude sickness (acute mountain sickness, or AMS) affects 25% to 50% of travelers who ascend above 8,000 feet (2,500 meters), according to the CDC. Symptoms typically begin 6 to 12 hours after arrival at high elevation and include headache, nausea, dizziness, and fatigue. Our clinical experience shows that most cases are preventable with proper acclimatization, and when that's not possible, prescription medications like acetazolamide (Diamox) reduce your risk by up to 48%. The key is understanding your risk before you go, not after you're already struggling to breathe at 14,000 feet.

Whether you're trekking to Everest Base Camp, hiking Machu Picchu, or flying into Cusco or Quito, this guide covers everything you need to know about altitude sickness: what causes it, how to spot the warning signs, and exactly what you can do to prevent it.

What Is Altitude Sickness?

Altitude sickness is your body's reaction to the reduced oxygen pressure at high elevations. At sea level, the atmosphere delivers oxygen at a pressure of about 760 mmHg. At 12,000 feet (3,650 meters), that pressure drops by roughly 40%, meaning each breath delivers significantly less oxygen to your bloodstream.

Your body can adapt to this change through a process called acclimatization, but it needs time. When you ascend faster than your body can adjust, fluid begins to leak into your brain and lungs, producing the cluster of symptoms we call altitude illness.

The CDC classifies altitude illness into three distinct syndromes, each progressively more serious:

Acute Mountain Sickness (AMS): The mildest and most common form. Feels like a bad hangover: headache, nausea, fatigue, poor appetite. Affects 25% to 43% of individuals ascending to elevations between 8,200 and 14,100 feet (2,500 to 4,300 meters), according to research published in the Journal of Travel Medicine.

High-Altitude Cerebral Edema (HACE): Swelling of the brain. Causes confusion, difficulty walking (ataxia), and altered consciousness. HACE is rare (affecting roughly 1% to 2% of travelers above 14,000 feet) but is a life-threatening emergency that requires immediate descent.

High-Altitude Pulmonary Edema (HAPE): Fluid accumulation in the lungs. Causes breathlessness at rest, a persistent cough (sometimes producing pink or frothy sputum), and extreme fatigue. HAPE occurs in approximately 0.1% to 4% of travelers above 8,200 feet and can be fatal within hours if untreated.

In our clinical practice, we've seen travelers return from trips with lingering symptoms they didn't recognize as altitude-related. Understanding these three syndromes is the first step toward protecting yourself.

Who Gets Altitude Sickness? Risk Factors Every Traveler Should Know

Altitude sickness does not discriminate based on fitness level. In fact, one of the most common misconceptions our providers encounter is fit, athletic travelers assuming they're immune. They're not. Research from the Wilderness Medical Society shows that physical fitness has no protective effect against AMS.

The primary risk factors include:

Rate of ascent. This is the single biggest factor. The CDC reports that AMS incidence increases 4.5 times faster when travelers ascend rapidly by air compared to gradual ascent on foot. Flying directly from sea level to a city like Cusco, Peru (11,152 feet / 3,400 meters) puts you at significantly higher risk than trekking there over several days.

Sleeping altitude. The elevation at which you sleep matters more than the highest point you reach during the day. This is why the mountaineering rule "climb high, sleep low" exists.

Home altitude. If you live at or near sea level, your body has zero baseline adaptation. Travelers from Denver (5,280 feet) have a meaningful advantage over travelers from Miami.

Individual susceptibility. Some people are genetically more prone to altitude sickness. If you've experienced AMS on a previous trip, you have about a 60% chance of experiencing it again at similar altitudes.

Age. Interestingly, younger travelers (under 46) may actually be slightly more susceptible to AMS than older travelers, possibly due to higher metabolic oxygen demand.

Pre-existing conditions. Travelers with coronary artery disease, chronic pulmonary conditions, obstructive sleep apnea, or sickle cell trait should consult a physician before traveling to high altitude, even if their condition is well-controlled.

Altitude Sickness Symptoms: What to Watch For

Recognizing altitude sickness early is critical because early symptoms are mild and easy to dismiss, especially when you're excited about your trip. Here's what to watch for at each stage.

Mild AMS Symptoms (Usually Appear 6 to 12 Hours After Arrival)

The hallmark symptom is a headache that doesn't fully respond to over-the-counter pain relievers. Alongside the headache, you may experience:

• Nausea or reduced appetite
• Dizziness or lightheadedness
• Fatigue and general malaise (feeling "off")
• Difficulty sleeping (insomnia is extremely common at altitude)

A useful clinical tool is the Lake Louise Acute Mountain Sickness Score, which grades symptoms on a scale of 0 to 3. A score of 3 or higher (with headache present) indicates AMS. The important thing to remember: if you feel unwell at altitude, assume it's altitude sickness until proven otherwise.

Moderate to Severe AMS Symptoms

If mild symptoms worsen or don't improve within 24 to 48 hours, the condition may be progressing. Warning signs include:

• Severe headache not relieved by ibuprofen or acetaminophen
• Persistent vomiting
• Increasing fatigue and weakness
• Shortness of breath with minimal exertion
• Decreased urine output (a sign of dehydration compounding altitude effects)

Emergency Warning Signs (HACE and HAPE)

These symptoms require immediate action, typically descent of at least 1,000 to 3,000 feet:

• HACE indicators: Confusion, disorientation, inability to walk a straight line (ataxia), drowsiness progressing to unconsciousness
• HAPE indicators: Breathlessness at rest, persistent wet cough, gurgling or rattling sounds when breathing, cyanosis (bluish discoloration of lips or fingertips), rapid heart rate

Our providers want to be direct: HACE and HAPE can kill. They are the leading causes of death related to high-altitude travel. If you or a travel companion develop these symptoms, descend immediately. Do not wait until morning. Do not "see how you feel." Descend.

Popular Travel Destinations and Their Altitudes

Understanding the altitude of your destination helps you assess your personal risk. Here are elevations for popular travel destinations that frequently cause altitude-related illness:

According to CDC data, approximately 200 million people travel to high-altitude destinations each year. If you're heading to any location above 8,000 feet, altitude sickness should be part of your pre-trip planning.

How to Prevent Altitude Sickness

Prevention is far more effective than treatment. Here's the evidence-based approach our clinical team recommends.

1. Gradual Acclimatization (The Gold Standard)

The CDC recommends travelers avoid ascending from low elevation to a sleeping altitude above 9,000 feet (2,750 meters) in a single day. The ideal approach:

• Spend 2 to 3 nights acclimatizing at 8,000 to 9,000 feet before going higher
• Once above 9,000 feet, increase your sleeping altitude by no more than 1,600 feet (500 meters) per day
• Build in a rest day (no altitude gain) for every 3,300 feet (1,000 meters) of elevation gained

This gradual approach is markedly protective against AMS. The challenge? Most travelers don't have unlimited vacation days. If you're flying directly into Cusco or Quito, gradual acclimatization isn't an option, which is where medication comes in.

2. Prescription Medication: Acetazolamide (Diamox)

Acetazolamide is the most studied and widely recommended medication for altitude sickness prevention. A systematic review and meta-analysis of randomized clinical trials found that acetazolamide reduces the incidence of AMS by approximately 48% compared to placebo.

How it works: Acetazolamide is a carbonic anhydrase inhibitor that causes a mild metabolic acidosis, which stimulates your breathing. This increases oxygen intake and accelerates the acclimatization process.

CDC-recommended dosing for prevention:

• 125 mg twice daily, starting 1 day before ascent and continuing for 2 days after reaching maximum altitude
• Some studies suggest doses as low as 62.5 mg twice daily may be effective, though 125 mg twice daily remains the standard recommendation

Common side effects: Tingling in fingers and toes (paresthesias), increased urination, altered taste of carbonated beverages, mild nausea. These side effects are generally mild and predictable.

Who should consider acetazolamide:

• Travelers flying directly to altitudes above 9,000 feet
• Anyone with a history of altitude sickness
• Travelers on tight itineraries who can't acclimatize gradually
• Trekkers ascending rapidly to very high altitudes

Acetazolamide requires a prescription. Through Wandr Health, you can get altitude sickness medication prescribed online and delivered before your trip, without needing a travel clinic appointment.

3. Dexamethasone (For High-Risk Situations)

Dexamethasone is a corticosteroid that prevents and treats AMS and HACE. The CDC recommends travelers carry dexamethasone for emergency treatment. It's typically reserved for:

• Travelers who cannot take acetazolamide (sulfa allergy)
• Emergency treatment of moderate to severe AMS or HACE
• High-risk ascent profiles where acetazolamide alone may be insufficient

Dosing: 4 mg every 6 to 12 hours for prevention; 8 mg initially followed by 4 mg every 6 hours for treatment of HACE.

Unlike acetazolamide, dexamethasone masks symptoms rather than aiding acclimatization. Once you stop taking it, symptoms can return if your body hasn't adapted.

4. Behavioral Prevention Strategies

Alongside medication and gradual ascent, these evidence-based strategies reduce your risk:

• Stay hydrated. Dehydration worsens altitude symptoms. Aim for 3 to 4 liters of water daily at altitude. Monitor your urine color: clear to pale yellow means adequate hydration.
• Avoid alcohol for the first 48 hours. Alcohol impairs breathing during sleep and worsens dehydration. That celebratory pisco sour in Cusco can wait.
• Eat carbohydrate-rich meals. Carbohydrates require less oxygen to metabolize than fats or proteins. A high-carb diet at altitude is associated with reduced AMS symptoms.
• Avoid sleeping pills. Sedatives can suppress breathing during sleep, worsening oxygen deprivation. If insomnia is an issue, acetazolamide actually improves sleep quality at altitude.
• Listen to your body. If you develop symptoms, do not ascend further until they resolve. This is the most ignored prevention rule in high-altitude travel.

How to Treat Altitude Sickness

If prevention fails and symptoms develop, here's the treatment approach, organized by severity.

Treating Mild AMS

Mild AMS generally resolves on its own within 12 to 48 hours if you stop ascending and allow your body to acclimatize. Treatment includes:

• Stop ascending. Rest at your current altitude until symptoms resolve.
• Acetazolamide (250 mg twice daily) accelerates recovery even when started after symptoms begin.
• Ibuprofen (600 mg every 8 hours) effectively treats altitude headache. A study in the Annals of Emergency Medicine found ibuprofen comparable to acetazolamide for treating mild AMS symptoms.
• Stay hydrated and eat light, carbohydrate-rich meals.
• Supplemental oxygen (if available) provides symptomatic relief.

Treating Moderate to Severe AMS

If symptoms persist beyond 24 hours or worsen despite rest:

• Descend. A descent of 1,000 to 3,000 feet (300 to 1,000 meters) typically produces rapid improvement.
• Dexamethasone (4 mg every 6 hours) for cases not responding to descent and acetazolamide.
• Portable hyperbaric chambers (Gamow bags) can simulate descent and provide temporary relief when physical descent isn't immediately possible.

Treating HACE and HAPE (Medical Emergencies)

HACE treatment:

• Immediate descent (minimum 1,000 feet, ideally 3,000+ feet)
• Dexamethasone 8 mg initially, then 4 mg every 6 hours
• Supplemental oxygen at 2 to 4 liters per minute
• Portable hyperbaric chamber if descent is delayed

HAPE treatment:

• Immediate descent
• Nifedipine 30 mg extended-release every 12 hours (reduces pulmonary artery pressure)
• Supplemental oxygen
• Minimize exertion (HAPE patients should be carried down if possible)

Both HACE and HAPE require evacuation to a medical facility. Do not attempt to "push through" these conditions.

When to See a Doctor Before Your Trip

Our clinical team recommends a pre-travel health consultation if any of the following apply:

• You're traveling to a destination above 9,000 feet (2,750 meters)
• You've experienced altitude sickness on a previous trip
• You have heart disease, lung disease, sleep apnea, or sickle cell trait
• Your itinerary involves rapid ascent (flying directly to high altitude)
• You're planning a trek above 14,000 feet

Wandr Health's free pre-trip health check evaluates your altitude sickness risk and can connect you with a physician who will prescribe the right medication for your specific trip, all online, without the $100+ consultation fee of a traditional travel clinic.

Altitude Sickness and Travel Insurance

One important consideration many travelers overlook: altitude sickness can lead to emergency evacuation, and helicopter rescue from places like the Himalayas or the Andes can cost $10,000 to $50,000 or more. Standard travel insurance policies vary widely in their coverage of altitude-related emergencies.

Before any high-altitude trip, confirm that your travel insurance covers emergency evacuation from altitude, including helicopter rescue if needed. Some policies exclude claims above certain elevations or require pre-authorization.

Frequently Asked Questions

How quickly does altitude sickness develop?

Altitude sickness symptoms typically begin 6 to 12 hours after arriving at high elevation, though some travelers notice symptoms within 1 to 2 hours. Symptoms usually peak at 24 to 72 hours. According to the CDC, acclimatizing for 2 to 3 nights at 8,000 to 9,000 feet before ascending higher significantly reduces this risk.

Can you die from altitude sickness?

Yes, though fatal cases are rare. High-altitude cerebral edema (HACE) and high-altitude pulmonary edema (HAPE) can be fatal within hours if untreated. AMS itself is not directly fatal, but ignoring symptoms and continuing to ascend can lead to HACE or HAPE. Approximately 0.1% to 4% of travelers above 8,200 feet develop HAPE.

Does physical fitness protect against altitude sickness?

No. Research from the Wilderness Medical Society confirms that physical fitness does not protect against acute mountain sickness. Elite athletes are just as susceptible as sedentary individuals. The only proven protective factors are gradual acclimatization, prior altitude exposure, and prophylactic medication.

How long does altitude sickness last?

Mild AMS typically resolves within 12 to 48 hours if you stop ascending and rest at your current altitude. With acetazolamide treatment, recovery may be faster. If symptoms don't improve within 24 hours or worsen at any point, descend to a lower elevation.

Is Diamox (acetazolamide) safe?

Acetazolamide has been used for altitude sickness prevention since the 1960s and has an extensive safety profile. Common side effects include tingling in the fingers and toes, increased urination, and altered taste of carbonated drinks. It is contraindicated in people with severe sulfa allergies, severe kidney or liver disease, and certain electrolyte disorders. A physician can determine if it's appropriate for you.

Should I take altitude sickness medication if I'm going to Colorado?

Colorado ski resorts range from 8,000 to 11,000 feet, and AMS affects roughly 25% of visitors. If you're flying in from sea level, especially for a short trip where you can't acclimatize gradually, acetazolamide is worth discussing with a physician. This is particularly relevant for travelers combining skiing with immediate physical exertion at altitude.

Can I just use ibuprofen instead of Diamox?

Ibuprofen (600 mg every 8 hours) has shown effectiveness in preventing and treating altitude headache specifically. However, it does not accelerate acclimatization the way acetazolamide does. For travelers at moderate risk, ibuprofen may be sufficient. For high-risk itineraries (rapid ascent, high target altitude, history of AMS), acetazolamide is the stronger choice.

When should I start taking acetazolamide before my trip?

The CDC recommends starting acetazolamide 1 day before you begin your ascent. Continue taking it for 2 days after reaching your maximum altitude, or for the duration of your time at high elevation. Starting earlier than 1 day before ascent does not provide additional benefit.

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Medical Disclaimer: This article is for informational purposes only and does not constitute medical advice. Start your visit on Wandr to discuss high-altitude travel plans with our providers before starting any medication or traveling to high altitudes with pre-existing medical conditions.

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Sources

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2. Acute Mountain Sickness. StatPearls, National Library of Medicine. https://www.ncbi.nlm.nih.gov/books/NBK430716/
3. Efficacy of acetazolamide for the prophylaxis of acute mountain sickness: A systematic review, meta-analysis, and trial sequential analysis. PMC. https://pmc.ncbi.nlm.nih.gov/articles/PMC8588948/
4. High-Altitude Illnesses: Physiology, Risk Factors, Prevention, and Treatment. PMC. https://pmc.ncbi.nlm.nih.gov/articles/PMC3678789/
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