Altitude Sickness

Altitude sickness is when your body doesn’t have time to adjust to lower oxygen availability higher up in the atmosphere. It’s usually preventable and treatable. When severe, it can rapidly turn into a life-threatening concern. Recognizing the symptoms early is key to pausing your ascent, which can head off complications or worsening symptoms.


What is altitude sickness?

Altitude sickness is the term for medical conditions that can happen when you move to a higher altitude too quickly. The higher up you go, the thinner the atmosphere gets. That means breathing in the same amount of air gets you less oxygen than at a lower altitude. Altitude sickness happens when your body has trouble adjusting to the difference in how much oxygen you’re getting with each breath.

Types of this condition

Altitude sickness can refer to three distinct conditions:

  • Acute mountain sickness (AMS). This is the mildest and most common form of altitude sickness.
  • High altitude pulmonary edema (HAPE). This is when altitude sickness affects your lungs, causing them to fill with fluid. It’s a medical emergency that needs immediate medical attention. While not the most severe form, it can cause death faster than other forms of altitude sickness.
  • High altitude cerebral edema (HACE). This is the most severe form. It happens when altitude sickness causes your brain to swell. It’s a very dangerous condition that needs emergency care.

How common is altitude sickness?

Altitude sickness is common among people who aren’t acclimated, meaning they’re not used to breathing at high altitudes. AMS is rare below 8,000 feet (2,438 meters) above sea level. Almost everyone who ascends quickly to 11,000 feet (3,352 meters) will develop AMS.


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Symptoms and Causes

What are the symptoms of altitude sickness?

Altitude sickness can cause many symptoms, and these can vary depending on the severity. The symptoms of acute mountain sickness usually appear within the first day or so of reaching a high altitude. More severe forms like HAPE or HACE take longer to appear, usually between two and five days.

The symptoms of AMS include:

  • Headache (this is the most common symptom).
  • Nausea and vomiting.
  • Loss of appetite.
  • Fatigue, even when resting.
  • Malaise (a noticeable “unwell” feeling).
  • Trouble sleeping.
  • Dizziness or lightheadedness.
  • Vision changes (while rare, these usually indicate more severe altitude sickness, and are due to blood vessel ruptures in your retinas).

What causes altitude sickness?

Given time, your body can usually adapt to altitude-related changes that affect how much oxygen you get with each breath. Without enough time to adapt, altitude sickness is the result.

What are the risk factors for altitude sickness?

The risk factors for altitude sickness often relate to the altitude itself or how you get there.

  • Higher altitudes: The higher you go, the greater your risk for altitude sickness.
  • Speed of ascent: Getting to a higher altitude quickly increases your risk of developing altitude sickness. People who fly to high altitudes rather than walk, hike or drive are much more likely to develop it. Above 8,000 feet, you should ascend no more than 1,640 feet (500 meters) per day.
  • Alcohol and drug (medical and nonmedical) use. Drinking alcohol or using certain medications, especially sedatives (either medical or nonmedical), can greatly increase the chances of developing altitude sickness.
  • History of altitude sickness. Having any form of altitude sickness, especially the more severe forms like HAPE or HACE, increases your risk of having it in the future.

A common misconception is that your physical health is a risk factor for developing altitude sickness. It isn’t, but altitude sickness can make symptoms of some existing conditions worse. Examples include anemia and chronic obstructive pulmonary disease (COPD).


What are the complications of altitude sickness?

Altitude sickness can become deadly if AMS turns into HAPE or HACE. HAPE can be deadly within 12 hours. HACE can be deadly within 24 hours. That’s why recognizing altitude sickness of any kind is critical to preventing severe complications.

Diagnosis and Tests

How is altitude sickness diagnosed?

A healthcare provider can diagnose altitude sickness based on your symptoms and a physical exam. That includes checking your breathing, blood pressure and heart rate. They’ll also ask questions about what you’re experiencing and how you feel. They may also check your coordination or other abilities to see if you have any signs of a more serious condition like HAPE or HACE.

What tests will be done to diagnose altitude sickness?

Altitude sickness often happens in locations that are remote and don’t have readily available medical equipment. By the time you descend to lower elevations where you can receive more advanced medical care, your symptoms are improved or gone entirely. However, medical testing is still possible when you reach a place where more advanced care is available.

Tests that may help diagnose or treat altitude sickness include:

  • X-rays. These can check your lungs for signs of HAPE, which causes fluid to fill your lungs.
  • Electrocardiogram (EKG). These can rule out other conditions like a heart attack. Some symptoms of altitude sickness are similar to heart attack symptoms, so an EKG may be necessary to rule out a heart attack.
  • Magnetic resonance imaging (MRI) scans. These can look for signs of swelling in your brain. MRI scans can also sometimes detect longer-lasting changes left behind by altitude sickness you had in the past.

Management and Treatment

How is altitude sickness treated, and is there a cure?

There’s only one way to “cure” altitude sickness outright: descend to a lower altitude.

Several treatments can help altitude sickness when it’s not as severe. Some of these are also helpful when an immediate descent isn’t possible. Treatment approaches include:

  • Stop and acclimate. Stopping and resting is a good idea at the first signs of altitude sickness.
  • Descend. If symptoms are more severe (such as additional dizziness, fatigue or nausea) or get worse, descending is a top priority. Most experts recommend descending until the symptoms get better. This usually involves a decrease of at least 984 feet (300 meters) and as much as 3,281 feet (1,000 meters).
  • Supplemental oxygen. Breathing higher concentrations of oxygen can help offset some of the symptoms of altitude sickness.
  • Medications. Certain medications, especially acetazolamide, dexamethasone or nifedipine, can treat altitude sickness and delay more severe symptoms or complications. Dexamethasone and nifedipine are generally reserved for moderate or worse altitude sickness.
  • Hyperbaric therapy. This is similar to treating a scuba diver with decompression sickness (better known as “the bends”). At high altitudes, hyperbaric therapy is possible with portable hyperbaric bags (sometimes known as “Gamow bags” after their inventor, Igor Gamow). These can delay the worsening of symptoms until it’s possible to evacuate a person to a lower altitude.

Complications/side effects of the treatment

Complications can vary depending on the treatment you receive, especially medications. Your healthcare provider is the best person to tell you what complications you might experience or should watch for.

How soon after treatment will I feel better?

How quickly you feel better depends strongly on the severity of your altitude sickness and the treatments you receive. Descending to a lower altitude is the fastest way to feel better, and most people feel progressively better as they descend.

People who choose to stop and acclimate may have symptoms that last several hours or up to a day. Minor symptoms usually stop within a day or two as your body gets used to the altitude.


Can altitude sickness be prevented?

Altitude sickness is very preventable, and there are a few key ways you can prevent it. They are:

  • Limit how fast you ascend. Altitude sickness is more likely when you ascend too far and too fast. A slower ascent is ideal for preventing altitude sickness. At 8,202 feet (2,500 meters), the recommendation is ascending no more than 984 feet (300 meters) to 1,640 feet (500 meters) per day. The starting altitude for the day is where you last slept. And if you ascend quickly early on because you flew to a high-altitude destination, factor that into your plans!
  • Take rest days to acclimate. At 8,202 feet (2,500 meters), experts recommend a day of initial rest to acclimate. If you continue ascending, rest every third day. Above 14,000 feet (4,267 meters), a two-day rest per 1,000 feet is recommended.
  • Sleep at a lower altitude if possible. If you can, ascend during the day and return to a lower altitude to sleep. That can make altitude sickness less severe and make it easier to acclimate.
  • Preventive medications. Medications like acetazolamide or nifedipine can prevent altitude sickness and treat it. Phosphodiesterase (PDE) inhibitors like sildenafil and tadalafil can also serve as preventive medications.

Outlook / Prognosis

What can I expect if I have altitude sickness?

For most people, altitude sickness doesn’t get beyond acute mountain sickness, the mildest form. A headache is the most common — and often the earliest — symptom of acute mountain sickness. If you notice you have a headache or other mild symptoms and stop ascending, your symptoms should remain the same. After a day or two, they should stop.

How long altitude sickness lasts

Milder forms of altitude sickness usually only last a few days. The symptoms should disappear once your body gets used to the higher altitude.

When altitude sickness is more severe, however, it can get worse quickly. The more severe forms of altitude sickness, HAPE and HACE, can be deadly within 24 hours. Because of that, keeping altitude sickness from worsening is critical. Recognizing the symptoms of HAPE and HACE, such as trouble breathing (even while resting) or clumsiness (ataxia), is crucial.

What’s the outlook for altitude sickness?

The outlook for altitude sickness depends on the severity, how you react to the symptoms and how you respond to treatment. If you ignore symptoms and keep ascending, you’ll likely experience worsening symptoms. Ascend too quickly, and you’re more likely to develop dangerous complications.

If you experience more disruptive symptoms of acute mountain sickness, especially nausea or fatigue, you should stop ascending. They’re a warning that you’re at risk for more problems if you keep going.

If you experience symptoms of HAPE or HACE, especially trouble breathing or loss of coordination, descend immediately (if possible). They’re signs of life-threatening complications.

Living With

How do I take care of myself?

If you develop symptoms of altitude sickness, the best thing you can do right away is not make it worse. Stop ascending, or descend if you can. Resting and limiting exertion are also helpful. Try to make it as easy as possible for your body to adjust to the altitude.

If you use tobacco products, you should quit before going to high altitudes. Tobacco use of any kind can affect oxygen levels, which is a key concern with altitude sickness. If you use tobacco products, stop. Your healthcare provider can guide you and offer resources on how to do so before you travel.

What can’t I eat or drink with altitude sickness?

If you have altitude sickness, modifying your diet is usually not necessary. But you should avoid alcohol for the first couple of days after you arrive at a high altitude. Alcohol can make some of the symptoms of altitude sickness worse. You should also be sure to get plenty of fluids to avoid dehydration, which can worsen some altitude sickness symptoms.

When should I see my healthcare provider, or when should I seek care?

You should talk to a healthcare provider before traveling to a high-altitude destination. They can advise you on precautions to take that’ll be helpful for your specific needs. They may also be able to advise you on preventive measures or prescribe medications that can prevent altitude sickness.

When should I go to the emergency room?

You should get emergency medical care (at a hospital, emergency room or another facility or setting that’s applicable) if you experience more serious symptoms of altitude sickness.

The most important symptoms to watch for are:

  • Shortness of breath, even when resting.
  • Chest tightness or pain.
  • Clumsiness or coordination problems.
  • Confusion.
  • Slurred speech.
  • Decreased consciousness.

These are all symptoms of more severe forms of altitude sickness. Both these other forms, HAPE and HACE, can be deadly within hours. Treating them as soon as possible is essential.

Additional Common Questions

How serious is altitude sickness?

The milder form of altitude sickness, acute mountain sickness, isn’t dangerous (as long as you don’t keep ascending). It’s unpleasant and disruptive but should resolve in a day or two.

The more severe forms of altitude sickness, HAPE and HACE, are life-threatening medical emergencies. They need immediate care.

A note from Cleveland Clinic

Altitude sickness is a widespread issue for people traveling to higher elevations. If you experience the symptoms, take them for the warning signs they are. Stop ascending and descend if you can. Resting and giving your body time to acclimate are the best ways to get past altitude sickness. Treatments can also help you feel better.

Altitude sickness is often very preventable. A flexible schedule can make a big difference, allowing time to acclimate to higher altitudes. Medications can also help. And if you experience more severe symptoms, don’t ignore them.

Medically Reviewed

Last reviewed by a Cleveland Clinic medical professional on 08/21/2023.

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