What is altitude sickness?

If you’ve ever hiked up a mountain and felt yourself getting nauseous or lightheaded, you may have experienced altitude sickness, also called mountain sickness. This condition happens when you travel to a high altitude (elevation) too quickly.

It doesn’t happen only to hikers. Just visiting a high-altitude location can cause problems for some. Symptoms happen when your body tries to adjust to the lower air pressure and lower oxygen levels at high altitudes.

Who is at risk for altitude sickness?

Anyone can get altitude sickness. Your age, sex and general health don’t seem to affect your risk. You may be at higher risk if you:

• Have a lung or heart condition: Your healthcare provider may recommend avoiding high altitudes if possible.
• Are pregnant: Talk to you provider before traveling to a high-altitude location.
• Live at low elevation: Since your body isn’t used to higher altitudes, you have a greater risk for symptoms. If you’re planning a trip to a high-altitude location, be aware of the symptoms of altitude sickness and how to treat it.
• Previously had altitude sickness: Talk to your provider about prevention and treatment before your next trip.

What is considered a “high elevation” in terms of getting altitude sickness?

Climbing to these elevations can bring on symptoms of altitude sickness:

• High altitude: 8,000 to 12,000 feet above sea level.
• Very high altitude: 12,000 to 18,000 feet.
• Extremely high altitude: 18,000+ feet.

For context, New York City is at an elevation of 33 feet above sea level. Denver (known as the “Mile High City”) sits at 5,000 feet, and many Rocky Mountain ski slopes are at 11,000 feet or higher. The Grand Canyon is 6,600 feet above sea level. The summit of Mount Everest is over 29,000 feet.

How common is altitude sickness?

Altitude sickness may occur in up to half of people who climb to elevations above 8,000 feet.

What are the different forms of altitude sickness?

Most people who get altitude sickness get AMS, acute mountain sickness. Higher than 10,000 feet, 75% of people will get mild symptoms . There are three categories of AMS:

• Mild AMS: Symptoms, such as mild headache and fatigue, don’t interfere with your normal activity. Symptoms improve after a few days as your body acclimates. You can likely stay at your current elevation as your body adjusts.
• Moderate AMS: Symptoms start to interfere with your activities. You may experience severe headache, nausea and difficulty with coordination. You’ll need to descend to start to feel better.
• Severe AMS: You may feel short of breath, even at rest. It can be difficult to walk. You need to descend immediately to a lower altitude and seek medical care.

Two severe forms of altitude illness occur less frequently but are more serious. Both can be life-threatening. You need to descend immediately and receive medical treatment for:

• HAPE (High-altitude pulmonary edema): HAPE produces excess fluid on the lungs, causing breathlessness, even when resting. You feel very fatigued and weak and may feel like you’re suffocating.
• HACE (High-altitude cerebral edema): HACE involves excess fluid on the brain, causing brain swelling. You may experience confusion, lack of coordination and possibly violent behavior.

What causes altitude sickness?

Altitude sickness results from a rapid change in air pressure and air oxygen levels at higher elevations. You may have symptoms if you travel to a high elevation without giving your body time to adjust to less oxygen. Even if you’re physically fit, you can still experience altitude sickness.

In addition, high altitude and lower air pressure can lead to fluid leaking from blood vessels. Researchers don’t understand exactly why this happens. This leakage causes fluid to build up in your lungs and brain. Ignoring moderate or severe symptoms can lead to a life-threatening situation.

What are the symptoms of altitude sickness?

You’ll likely feel nauseous and lightheaded. You may vomit and have a headache. Different levels of altitude sickness have different symptoms:

Symptoms of mild, short-term altitude sickness usually begin 12 to 24 hours after arriving at high altitude. They lessen in a day or two as your body adjusts. These symptoms include:

• Dizziness.
• Fatigue and loss of energy.
• Shortness of breath.
• Loss of appetite.
• Sleep problems.

Symptoms of moderate altitude sickness are more intense and worsen instead of improve over time:

• Worsening fatigue, weakness and shortness of breath.
• Coordination problems and difficulty walking.
• Severe headache, nausea and vomiting.
• Chest tightness or congestion.
• Difficulty doing regular activities, though you may still be able to walk independently.

Severe altitude sickness is an emergency. The symptoms are similar to moderate AMS, but more severe and intense. If you start experiencing these symptoms, you must be taken to a lower altitude immediately for medical care:

• Shortness of breath, even when resting.
• Inability to walk.
• Confusion.
• Fluid buildup in the lungs or brain.

HAPE, when fluid builds up in the lungs, prevents oxygen from moving around your body. You need medical treatment for HAPE. Symptoms include:

• Cyanosis, when your skin, nails or whites of your eyes start to turn blue.
• Confusion and irrational behavior.
• Shortness of breath even when resting.
• Tightness in the chest.
• Extreme fatigue and weakness.
• Feeling like you’re suffocating at night.
• Persistent cough, bringing up white, watery fluid.

HACE happens when the brain tissue starts to swell from the leaking fluid. You need medical treatment for HACE. Symptoms include:

• Headache
• Loss of coordination.
• Weakness.
• Disorientation, memory loss, hallucinations.
• Psychotic behavior.
• Coma.

How is altitude sickness diagnosed?

If you get a headache and at least one other symptom with 24 to 48 hours of moving to a higher elevation, it’s most likely altitude sickness. If you’re climbing, a more experienced climber may recognize symptoms of altitude sickness and guide you to get help.

If you have severe altitude sickness, a healthcare provider will ask about your symptoms, activities and location. The provider may perform a physical exam, including listening to your chest.

Will I need tests to diagnose altitude sickness?

You may need a chest X-ray to see if there is any fluid in your chest. In severe cases, your healthcare provider may order a brain MRI or CT scan to check for fluid in the brain.

How is altitude sickness treated?

The main treatment for altitude sickness is to move to a lower elevation as quickly and safely as possible. At the very least, do not go higher. If symptoms are mild, staying at your current elevation for a few days might be enough to improve the symptoms.

Other treatments depend on how severe the symptoms are:

• Mild altitude sickness: Over-the-counter medicines can relieve headaches. Other symptoms will improve once your body adjusts or you move to a lower altitude.
• Moderate altitude sickness: Symptoms should improve within 24 hours once you are 1,000 to 2,000 feet lower than you were. Within three days, you should feel completely better.
• Severe altitude sickness, HACE and HAPE: If you have severe symptoms, you must be taken immediately to an elevation that’s no higher than 4,000 feet. Get to a healthcare provider as soon as possible. You may need hospitalization.

What treatments are available for severe altitude sickness?

Treatments depend on your symptoms:

• For fluid in the brain (HACE), you may need dexamethasone, a steroid that helps reduce swelling in the brain. Dexamethasone is sometimes prescribed as a preventive medication.
• For fluid in the lungs (HAPE), you may need oxygen, medication, a lung inhaler or, in severe cases, a respirator.
• If you need more oxygen, a provider might prescribe acetazolamide, which increases your breathing rate, so you take in more oxygen. The medicine helps your body adjust faster to the higher elevation and reduces symptoms of altitude sickness.

How can altitude sickness be prevented?

The best way to prevent altitude sickness is to go slow — called acclimatization. This process allows your body time to adjust to the change in oxygen levels. Take your time when traveling up. For instance, spend a day at a point midway up before continuing to ascend.

You can also talk to your healthcare provider about taking acetazolamide before your trip. Taking it 24 hours before traveling to a high altitude and continuing for five days can help prevent altitude sickness. Dexamethasone can also be used preventively, but it can have serious side effects. Talk to your provider before your trip.

What’s the outlook for someone with altitude sickness?

Most people who get altitude sickness get the mild form. Once you return to a lower elevation (or stay at your current elevation without climbing higher), symptoms improve.

Are there long-term effects of altitude sickness?

If you take care and move to a lower elevation when you feel symptoms, altitude sickness has no long-term negative effects. You’ll recover within a few days. Once you feel better, you can continue to travel to higher elevations, as long as you do so slowly and carefully.

Can altitude sickness be fatal?

In rare cases, altitude sickness can be life-threatening. If you develop HAPE or HACE, you are at risk for complications such as coma or even death. Get treatment as soon as possible to reduce your risk.

Can altitude sickness be cured?

Altitude sickness is temporary. Once you return to a lower altitude, you’ll feel better. When you begin your ascent again (or on your next climb), make sure to travel slowly to let your body acclimate.

If I’m planning a hike to a very high elevation, how can I hike safely without getting altitude sickness?

These steps can help your body acclimate:

• Walk up: Start below 10,000 feet and walk to a high altitude instead of driving or flying. If you drive or fly to an elevation higher than 10,000 feet, stay at your first stop for at least 24 hours before going higher.
• Go slow: Once above 10,000 feet, don’t increase your altitude more than 1,000 feet a day.
• Rest: Build a rest day into your schedule for every 3,000 feet you climb.
• “Climb high and sleep low”: If you climb more than 1,000 feet in a day, come down to sleep at a lower altitude.
• Know your body: Recognize the signs and symptoms of altitude sickness. Move to a lower altitude (or avoid climbing higher) if you notice any symptoms.
• Stay hydrated: Drink 3-4 quarts of water per day.
• Avoid alcohol: Alcohol can dehydrate your body. It also has stronger effects at higher elevations, which can impair judgment.
• Eat carbs: Eat a diet that’s more than 70% carbohydrates.
• Know the “don’ts”: Avoid tobacco and depressant drugs, such as sleeping pills and tranquilizers.

What should I ask my doctor?

If you’re planning to travel to high altitudes, ask your healthcare provider:

• Should I take a preventive medication to avoid altitude sickness?
• Do I have any risk factors that would prevent me from visiting high elevations?
• What other steps can I take to prevent altitude sickness?
• What steps should I take if I start to feel symptoms during my climb?

A note from Cleveland Clinic

Altitude sickness symptoms can range from uncomfortable to life-threatening. But with some planning and precautions, you can avoid this condition. The best way to prevent it is to move at a slower pace and let your body adjust. If you notice symptoms at high elevation, don’t push yourself to go farther. Get back down to a lower elevation and let your body adjust before moving up, slowly and carefully.