Skip to main content

Altitude Sickness

Medically reviewed by Last updated on Jan 3, 2022.

What is altitude sickness?

Harvard Health Publishing

At higher altitudes, the pressure of the air around you (barometric pressure) decreases so there is less oxygen in surrounding air. People can live comfortably at moderately high altitudes, but the body must make some adjustments, and this takes time. If you ascend to altitudes above 8,000 feet, you will be in danger of developing uncomfortable or dangerous symptoms from the change in altitude.

Symptoms of altitude sickness that are not life threatening are called acute mountain sickness. Mountain climbers on any high mountain and skiers in high-altitude locations such as Colorado are at risk of developing acute mountain sickness. Symptoms from acute mountain sickness improve if you descend to lower altitude quickly. For very mild symptoms, a delay before further climbing may be enough to allow symptoms to go away.

Acute mountain sickness is the least dangerous of several kinds of altitude illnesses that can occur. This sickness affects close to half of all people who begin near to sea level and climb to 14,000 feet of elevation without scheduling enough rest time.

Symptoms that develop at high altitude should be taken very seriously, since some altitude problems can develop into fatal illnesses. One dangerous reaction to high altitude is a condition called high-altitude cerebral edema (HACE), in which the brain accumulates extra fluid, swells and stops working properly. A related illness, high-altitude pulmonary edema (HAPE), can occur with or without warning symptoms that signal altitude sickness. HAPE causes fluid to enter the lungs. A type of altitude sickness called high-altitude retinal hemorrhage (HARH) can cause eye damage. Coma and death are the most serious consequences of altitude sickness.

Altitude sickness is more likely to occur in people who have a previous history of altitude sickness. It is more likely if you climb quickly, if you exercise vigorously during your first few days of altitude exposure, and if you have been living at low elevation prior to your climb. Obesity appears to increase the risk for altitude sickness. Genetics may also put some people at increased risk, particularly for high altitude pulmonary edema (HAPE).

Symptoms of altitude sickness

As your body makes normal adjustments to adapt to a high altitude, you may experience a few symptoms that are bothersome but are not cause for concern. They include rapid (but still comfortable) breathing, shortness of breath with strenuous exercise, occasional short pauses in breathing while you sleep, and frequent urination. The last two symptoms are caused by a low carbon dioxide level, which triggers adjustments in the brain and kidney.

More serious symptoms are caused by low levels of oxygen in the blood and adjustments that are made by your circulation system.

Acute mountain sickness usually causes symptoms at least 8 to 36 hours after ascent.

Symptoms of acute mountain sickness can include:

High-altitude cerebral edema is considered by many experts to be an extreme form of acute mountain sickness. It usually develops after symptoms of acute mountain sickness. Symptoms of this more severe altitude disease may not be noticed immediately because the illness can begin during the night. Because this low-oxygen injury affects the brain and thought process, a person with high-altitude cerebral edema may not understand that symptoms have become more severe until a traveling companion notices unusual behavior.

Symptoms may include:

  • Worsening headache and vomiting
  • Walking with a staggering gait
  • Confusion
  • Exhaustion
  • Visual hallucinations (seeing things that are not real)
  • Changes in the ability to think
  • Changes in normal behavior
  • Coma (in advanced cases)

High-altitude pulmonary edema, which is the lungs' response to an increase in altitude, may occur with or without other symptoms of altitude illness. A low oxygen concentration can trigger blood vessels in the lungs to constrict (tighten), causing a higher pressure in the lung arteries. This causes fluid to leak from the blood vessels into the lungs. Symptoms of high-altitude pulmonary edema commonly appear at night and can worsen during exertion.

Symptoms of high-altitude pulmonary edema include:

  • Chest tightness or fullness
  • Extreme fatigue
  • Inability to catch your breath, even when resting
  • Blue or gray lips and fingernails
  • Coughing, which may produce pink frothy fluid
  • Fever (temperature is above normal but is less than 101° Fahrenheit)
  • Noises when breathing, such as rattling or gurgling sounds

High-altitude retinal hemorrhage can occur with or without symptoms. It usually is not noticeable unless the area of the eye that provides the most detailed vision (the macula) is involved.

Blurred vision is the main symptom of high-altitude retinal hemorrhage.

Diagnosing altitude sickness

You must be able to recognize the early symptoms of altitude sickness, and you should watch carefully for symptoms when you are at risk because altitude illnesses can be life threatening.

If headache is your only symptom, you should stop climbing and take a mild pain reliever. If you have a headache that does not go away or if you have other symptoms that suggest acute mountain sickness, this illness can be diagnosed without tests.

High-altitude cerebral edema can make it difficult to walk a straight line, and can lead to changes in thinking, hallucinations or an unexplained change in personality. If a person has these symptoms at high altitude, you should assume that the person has high-altitude cerebral edema. A person with these symptoms should descend immediately and seek medical care. Once a person with high-altitude cerebral edema has been transported to a medical center, a magnetic resonance imaging (MRI) scan may be done to confirm the cause of the symptoms. An MRI can show brain swelling.

Recognizing high-altitude pulmonary edema can be difficult in its early stages because fatigue may be the only sign. Symptoms that should be of concern include difficulty exercising, dry cough, rapid heart rate (more than 100 beats per minute), and shortness of breath while resting. Listening to the lungs with a stethoscope may reveal a crackling noise with each breath. If blood oxygen levels were measured, they would be lower than expected for your altitude. X-rays may show signs of fluid filling one or more areas within the lungs, giving an appearance that is similar to pneumonia.

High-altitude retinal hemorrhage can be diagnosed by a doctor who examines the eye with a hand-held instrument called an ophthalmoscope.

Expected duration of altitude sickness

If you are climbing and do not move back down to an elevation where you last felt well, your symptoms can worsen and can be deadly. Symptoms from acute mountain sickness will go away after two or three days of rest at a lower altitude. Severe syndromes such as HAPE can take weeks to disappear, and will require medical attention and possible hospitalization.

Preventing altitude sickness

Gradual changes in altitude will help your body adapt to the low-oxygen environment and can reduce your chances of developing all forms of altitude sickness. People adapt at different rates, but there are four general guidelines for climbing above 10,000 feet that are practical for climbers to follow:

  • Do not increase your altitude by more than 1,000 feet per night.
  • Each time you increase your altitude by 3,000 feet, spend a second night at this elevation before going farther.
  • Limit your physical exertion to reasonable levels during your first few days of ascent to altitude.
  • Drink plenty of fluid during your altitude exposure.

If you develop early signs of altitude sickness, you can keep from getting worse if you immediately stop ascending or if you descend.

Mild symptoms of altitude adjustment, such as headache, can be prevented or at least limited by taking ibuprofen.

If you have experienced high-altitude illness in the past and are planning to again go to high altitude, you should get a prescription for acetazolamide (Diamox, generic versions) to take with you. All the measures noted above are most important, but you may want to start taking the drug as you reach higher altitudes. Acetazolamide can cause frequent urination, tingling in the fingers and toes and a metallic taste in the mouth.

If you previously have developed HAPE, you may receive the oral drug nifedipine (Procardia), the inhaled drug salmeterol (Serevent), or both medicines for a future rise to altitude. These medications may stabilize the blood-flow pattern in your lungs.

Treating altitude sickness

The first rule of treatment for mild symptoms of acute mountain sickness is to stop ascending until your symptoms are completely gone. If you have more severe symptoms or any symptoms of high-altitude cerebral edema, high-altitude pulmonary edema, or blurred vision, you need to move to a lower altitude as soon as possible, even if it's the middle of the night. If you remain at your current altitude or continue going higher, the symptoms will get worse and the sickness can be fatal.

Besides moving to a lower altitude, you can treat mild altitude sickness with rest and pain relievers. The drug acetazolamide can speed recovery. This drug balances your body chemistry and stimulates breathing.

If you have symptoms of altitude sickness, avoid alcohol, sleeping pills and narcotic pain medications. All of these can slow your breathing, which is extremely dangerous in low-oxygen conditions.

If a descent must be delayed — you can treat high-altitude cerebral edema with supplemental oxygen and the drugs acetazolamide and dexamethasone, which help decrease brain swelling. If one is available, this condition is also helped by time spent in a portable hyperbaric (pressure) chamber, which simulates descent to a lower altitude, during the time that supervision and transportation arrangements are being made for descent to lower altitude.

Treatment for high-altitude pulmonary edema is similar, but may also include oral nifedipine and inhaled salmeterol.

When To Call A Professional

People with altitude sickness may not realize they are ill or that their symptoms are worsening. If you are accompanying someone who has symptoms of altitude sickness, help that person move to a lower altitude and consult a doctor as soon as one is available.


The outlook for altitude sickness depends on how quickly the person can be moved to a lower altitude, and how serious their symptoms are. Symptoms of altitude sickness can disappear in just a few days at lower altitudes. In many cases, activities at high altitude can be resumed. However, the condition can be fatal if the symptoms are severe and the person remains at a high altitude.

Additional Info

National Library of Medicine (NLM)

American Heart Association (AHA)

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.