Altitude Sickness (Mountain Sickness)

Reviewed on 6/17/2022

Things to Know About Altitude Sickness (Mountain Sickness)

Fatigue, insomnia, and headaches are early symptoms of altitude sickness.
Fatigue, insomnia, and headaches are early symptoms of altitude sickness.

What is the medical definition of altitude sickness?

  • Altitude sickness is due to a rapid ascent to higher altitudes (4800 to 11,200 ft or more) due to the decreasing amount of oxygen (low PO2) that occurs at high altitudes.
  • There are three main types of altitude sickness, acute (mild) altitude or mountain sickness (AMS), high-altitude pulmonary edema (HAPE), and high-altitude cerebral edema.
  • The cause of altitude sickness is the decreasing amount of oxygen available as altitude increases.

What are the first signs of altitude sickness?

  • Early symptoms of altitude sickness include
  • Later symptoms include
    • shortness of breath,
    • extreme fatigue,
    • respiratory failure,
    • cerebral edema,
    • coma, and
    • death.
  • Although many people with mild acute mountain sickness require no medical care, as symptoms worsen, emergency medicine physicians, hyperbaric chamber experts, neurologists, and critical care specialists may need to be consulted.
  • Altitude sickness is usually diagnosed by the patient's clinical condition. Occasionally other tests such as chest X-rays, head CTs, and/or MRI scans are utilized.

What is the best remedy for altitude sickness?

  • Some people can use self-care or home remedies, such as simply descending to a lower altitude, to help reduce symptoms or cure altitude sickness.
  • Medical treatment for altitude sickness may include oxygen, hyperbaric treatment, and medicines such as acetazolamide (Diamox, Diamox Sequels) and/or dexamethasone (AK-Dex, Ocu-Dex) as well as over-the-counter (OTC) pain medications and antinausea medications. However, definitive treatment is for the patient to go to a lower altitude.
  • Most people with self-curing acute mountain sickness do not need a follow-up with a healthcare professional. However, those that develop high-altitude pulmonary edema and/or high-altitude cerebral edema may require more extensive follow-up with their doctors.
  • The prevention of altitude sickness is by acclimatizing the body to increasing altitude. Prevention of acute mountain sickness is sometimes with acetazolamide medication.

How long does altitude sickness last?

  • The prognosis for a person that gets altitude sickness depends on the severity of the sickness. Acute mountain sickness can usually resolve with no problems, but patients that develop high-altitude pulmonary edema and/or high-altitude cerebral edema have a more guarded prognosis. About 50% of individuals that develop coma with high-altitude cerebral edema die.

What does someone with altitude sickness look like (pictures)?

 High-altitude pulmonary edema (HAPE). Image courtesy Dr Peter Hackett.
High-altitude pulmonary edema (HAPE). Image courtesy Dr. Peter Hackett.

Hyperbaric treatment at 4250 m in a Gamow bag.
Hyperbaric treatment at 4250 m in a Gamow bag.

What Is Altitude Sickness?

Altitude sickness (sometimes termed mountain sickness) is an illness due to the decreasing the amount of oxygen at above sea level altitudes ranging usually about 4800 ft or 1500 m that may range from a mild headache and weariness to a life-threatening build-up of fluid in the lungs or brain, and even fatality at moderate to high altitudes.

Altitude sickness usually occurs when people travel from lower altitudes in less than one day to higher altitudes (8000 feet or 2438 m or higher), but depending upon the individual's health, altitude sickness may occur at considerably lower altitudes, even 4800 feet or 1500 m. Altitude sickness has a spectrum of symptoms and is a general term that covers three major syndromes.

  1. Acute mountain sickness (AMS)
  2. High-altitude pulmonary edema (HAPE)
  3. High-altitude cerebral edema (HACE)

In this article:

  • Moderate to high-altitude is considered 4800 feet to about 6400 feet (1500-2000 m) above sea level
  • High-altitude is considered to be about 6400 to 11,200 feet (2000-3500 m)
  • Very high altitude is considered 11,200 feet to 18,000 feet (3500-5600 m)
  • Extreme altitude is above 18,000 feet.

High-altitude cerebral edema and high-altitude pulmonary edema most commonly occur at very high-altitude; however, they can occur in some people at high altitudes.

What Is Acute Altitude Sickness?

Acute altitude sickness or acute mountain sickness is the mildest and most common form of altitude sickness. Because more people are traveling to areas of high elevation for recreational and professional sports, for example, skiing, hiking, mountain climbing, and biking; acute mountain sickness has become a greater public health concern. Roughly one-fourth of Colorado ski area vacationers, two-thirds of climbers on Mount Rainier, and half the people who fly to the Khumbu region of Nepal develop acute altitude sickness.

A more serious form of altitude sickness is high-altitude edema. This illness occurs when fluid builds up within the lungs, a condition that can make breathing extremely difficult. Usually, this happens after the second night spent at a high altitude, but it can happen earlier or later.

What is high-altitude pulmonary edema?

High-altitude pulmonary edema often comes on quickly. If left untreated, it can progress to respiratory collapse and ultimately to death. High-altitude pulmonary edema is the number one cause of death from altitude sickness.

What is high-altitude cerebral edema?

A severe form of altitude sickness is high altitude cerebral edema, in which fluid builds up within the brain. As the brain swells with fluid, the person's mental state changes. Loss of coordination, coma, and, finally, death can follow unless the problem is recognized and treated promptly.

What Are the Early Signs and Symptoms of Altitude Sickness?

Early symptoms of acute altitude sickness are usually the following:

However, acute altitude sickness may be associated with any combination of the following symptoms:

What are the late symptoms of acute altitude sickness?

Late symptoms of acute altitude sickness include:

  • Swelling of extremities (late symptom)
  • Social withdrawal (late symptom)

People with acute altitude sickness often attribute their symptoms to other causes such as an uncomfortable bed, bad food, or a hangover. However, it is important to recognize that these symptoms may indicate a high-altitude illness.

What Are the Signs and Symptoms of High-Altitude Pulmonary Edema?

High-altitude pulmonary edema, an advanced form of altitude sickness, causes the following progression of symptoms to develop. The person may have:

  • Several of the acute mountain sickness symptoms develop slowly or rapidly (early symptoms)
  • Shortness of breath at rest (early symptom)
  • Gurgling respirations
  • A wet cough with frothy sputum
  • A fever
  • Respiratory failure (late symptom)

The onset of high-altitude pulmonary edema can be gradual or sudden. High-altitude pulmonary edema typically occurs after more than one day spent at a high altitude. High-altitude pulmonary edema requires immediate treatment.

What Are the Signs and Symptoms of High-Altitude Cerebral Edema?

High-altitude cerebral edema produces symptoms that can become progressively worse over a short time period.

  • Any acute mountain sickness or high-altitude pulmonary edema symptoms (early symptoms)
  • confusion (early symptom)
  • Cannot do usual functions (hiking, skiing, for example) because of fatigue or shortness of breath
  • Walking and coordination become impaired.
  • As the brain continues to swell, lethargy and then coma will develop (late symptoms).
  • If left untreated, high-altitude cerebral edema will ultimately result in death.

What Are the Causes of Altitude Sickness?

Altitude sickness develops when the rate of ascent into higher altitudes outpaces the body's ability to adjust to those altitudes due to the decreasing levels of oxygen in the air as altitude increases. This results in abnormally low blood levels of oxygen.

Altitude sickness generally develops at elevations higher than 8,000 feet (about 2,400 meters) above sea level and when the rate of ascent exceeds 1,000 feet (300 meters) per day.

The following actions can trigger altitude sickness:

  • Ascending too rapidly (not allowing enough time for the body to compensate for decreased oxygen in the air)
  • Overexertion within 24 hours of ascent
  • Inadequate fluid intake
  • Hypothermia
  • Consumption of alcohol o or other sedatives

It is possible, depending on the person's health, that an individual can rapidly go through symptoms of acute mountain sickness and then progress to high-altitude pulmonary edema or high-altitude cerebral edema at moderate to high altitudes.

Which Doctors Treat Altitude Sickness?

The initial treatment for altitude sickness is no further ascent in altitude. If symptoms do not resolve quickly, descend to a lower altitude. If the person develops any signs and symptoms of high-altitude cerebral edema or high-altitude pulmonary edema, they should descend to a lower altitude and be seen by an emergency medicine physician.

Other physicians that may be involved in the care of the patient may be a hyperbaric-trained physician, neurologist, and/or pulmonary or critical care specialist, depending on the severity of symptoms.

When Should a Person Seek Medical Care for Altitude Sickness?

If symptoms such as headache or shortness of breath do not improve promptly with simple changes, visiting a doctor may be helpful if descending to a lower altitude is inconvenient and a doctor is available.

Descend immediately if shortness of breath at rest, mental confusion or lethargy, or loss of muscle coordination develop. Symptoms of most people with acute altitude sickness improve by the time they reach a medical facility, which is usually located at a lower altitude.

How Do Doctors Diagnose Altitude Sickness?

The diagnosis of acute altitude sickness is based on the patient's signs and symptoms. After traveling to a high altitude, symptoms of loss of appetite, generalized weakness, dizziness, shortness of breath during exertion, nausea, or a headache associated with insomnia may indicate altitude sickness.

  • The doctor may hear crackles or rales (a rattling sound) when listening to the patient's lungs.
  • Shortness of breath at rest may indicate high-altitude pulmonary edema.
  • The patient's vital signs may be abnormal and may include low-grade fever and faster-than-normal heart and breathing rates.
  • Pulse oximetry, which measures oxygen saturation of the blood, may reveal that the patient's oxygen saturation is lower than expected for that particular altitude.
  • The doctor may treat the patient with fever and cough for pneumonia in addition to high-altitude pulmonary edema.
  • High-altitude cerebral edema is diagnosed if a person's mental state is altered or coordination is lost at a high altitude.

What Self-Care or Home Remedies Soothe or Cure Altitude Sickness?

  • Delay further ascent until symptoms improve.
  • Rest and stay warm.
  • Take acetaminophen (Tylenol) for headaches.
  • Do not use sleeping pills or other central nervous system depressants to treat insomnia because they can suppress breathing.
  • If symptoms continue, do not travel any higher and consider descending to a lower altitude.
  • If symptoms worsen, descend approximately 1,000-2,000 feet (300-600 meters) immediately.
  • If descent is not possible, a portable hyperbaric chamber (Gamow bag) can be used to simulate a lower altitude.
    • The higher the altitude at which a hyperbaric chamber is used, the greater the apparent descent can be simulated. (This is because portable hyperbaric chambers can increase atmospheric pressure by 2 pounds per square inch.)
    • For example, a hyperbaric chamber at 9,800 feet (3,000 meters) can simulate a descent of 4,800 feet (1,500 meters), but the same hyperbaric chamber used at 24,600 feet (7,500 meters) can simulate a descent of 7,800 feet (2,400 meters).

What Is the Medical Treatment for Altitude Sickness Treatment?

Descending to lower altitudes (about 1640-3280 feet or 500-1000 meters lower altitude than the altitude the person was at when symptoms developed) or delaying further ascent are treatments for altitude mountain sickness until symptoms are gone.

  • A Gamow bag may be used if descent is not feasible (see previous sections for details).
  • Oxygen (2-4 liters per minute) will improve the oxygen saturation of the blood.
  • Aspirin, acetaminophen (Tylenol), or ibuprofen (Advil, Motrin) may be taken for headaches (do not give aspirin to children).
  • For nausea, the doctor may prescribe prochlorperazine (Compazine), an antinausea medication that also enhances the body's ability to increase the breathing rate in response to low-oxygen environments. Other antiemetics have been used (for example, ondansetron (Zofran).
  • Sleeping pills for insomnia should not be taken. They are potentially dangerous because they can slow breathing. However, some doctors still may prescribe them under certain circumstances.
  • Acetazolamide (Diamox) may be prescribed to hasten acclimatization.
    • Acetazolamide is a diuretic (a drug that increases urine output) that increases kidney excretion of bicarbonate. This decreases the blood pH, thereby stimulating extra breathing, which results in higher oxygen levels in the blood.
    • In addition, acetazolamide corrects nighttime pauses in breathing known as periodic breathing. Acetazolamide also improves symptoms of insomnia.
    • This medication may also be utilized in a preventative manner in people with a prior history of altitude sickness.

High-altitude pulmonary edema responds best when the person descends from their current altitude.

  • Oxygen, if available, should be provided.
  • Nifedipine (Procardia), a medication for high blood pressure, has been shown to be beneficial for high-altitude pulmonary edema.
  • Antibiotics may be given if a fever is present and pneumonia is possible.
  • For more severe cases of high-altitude pulmonary edema, continuous positive airway pressure (CPAP) mask ventilation can be used. Although uncomfortable to wear, the CPAP mask helps by increasing the pressure of the inhaled air.
  • If this intervention fails, a tube may be placed through the mouth and into the airway (intubation). This, along with assisted ventilation, is required to treat respiratory failure.

The only definitive treatment for high-altitude cerebral edema is descent from the person's current altitude.

  • Dexamethasone (Decadron), a steroid, may be beneficial.
    • Generally, if xamethasone is considered, then a plan for descent should be in place unless descent is impossible.
    • Some people, after receiving dexamethasone, may feel so much better that they want to continue ascending. Under no circumstance should this be allowed?
  • Oxygen may be helpful.
  • A Gamow bag may buy time until descent is possible.

Anyone with high-altitude cerebral edema or high-altitude pulmonary edema should be kept as comfortable as possible.

  • Exertion of any type should be minimized, even during descent
  • This means that it may be necessary to arrange descent for the ill person by whatever means available (helicopter, snowmobile, or mule, for example).

Do I Need to Follow-up With a Doctor After an Episode of Altitude Sickness?

Mild acute mountain sickness that resolves quickly usually does not need to require follow-up with a healthcare professional. However, if one is seen, proceed with the following instructions:

  • Follow instructions regarding activity limitation, use of additional oxygen, postponement of climbing, or immediate descent, if required.
  • Take medications as prescribed.
  • Do not drink alcohol, and avoid smoking tobacco, especially while at a high altitude.
  • Keep any follow-up appointments.
  • Seek medical attention immediately if symptoms worsen or if new symptoms develop.

Is It Possible to Prevent Altitude Sickness?

Altitude sickness is preventable. The body needs time to adjust to high altitudes. Physical conditioning has no bearing on this. So everyone, including children and infants, maybe at some risk when ascending to higher altitudes.

  • For people who do not know the rate at which their bodies adjust to high altitudes, the following preventive measures are recommended.
    • If traveling by air to a ski area above 8,250 feet (2,500 meters), incorporate a layover of 1-2 days at an intermediate altitude.
    • Avoid physical exertion for the first 24 hours.
    • Drink plenty of fluids, and avoid alcoholic beverages.
    • Consume a high-carbohydrate diet.
    • If mountain climbing or hiking, ascend gradually once past 8,000 feet (2,400 meters) above sea level.
    • Increase the sleeping altitude by no more than 1,000 feet (300 meters) per 24 hours. The mountaineer's rule is "climb high, sleep low." This means that on layover days, a climber can ascend to a higher elevation during the day and return to a lower sleeping elevation at night. This helps to hasten acclimatization.
  • The doctor may prescribe acetazolamide (Diamox) to prevent acute altitude sickness. This medication speeds acclimatization.
  • If rapid ascent is unavoidable, as in rescue missions, or if a person is prone to developing high-altitude pulmonary edema, the doctor may also prescribe nifedipine (Procardia). Nifedipine is normally used to treat high blood pressure.
  • Prevention of high-altitude cerebral edema and/or high-altitude cerebral edema is the same as acute altitude sickness.

What Is the Outlook for a Person Who Gets Altitude Sickness?

The prognosis for acute altitude sickness is excellent as long as common sense is used. Descending, delaying further ascent, resting, and paying attention to the body's symptoms are usually all that is necessary to ensure a complete recovery.

High-altitude pulmonary edema has a good outcome if symptoms are recognized and treated early. If descent is impossible or if hyperbaric therapy, supplemental oxygen, and access to medical care are not available, high-altitude pulmonary edema can progress to respiratory failure and ultimately to death. High-altitude pulmonary edema is the number one cause of death from high-altitude illness.

More than half of people with high-altitude cerebral edema who develop a coma die. Of those who survive, mental impairment and coordination defects may continue to affect them. High-altitude cerebral edema can be fatal if not recognized and treated quickly.

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Acute Altitude Sickness Symptoms

The symptoms of altitude sickness include:

  • A throbbing headache that usually gets worse during the night and when you wake up.
  • Lack of appetite
  • Feeling sick to your stomach. You may vomit.
  • Feeling weak and tired. In severe cases, you do not have the energy to eat, dress yourself, or do anything.
  • Waking up during the night and not sleeping well.
  • Feeling dizzy.
Reviewed on 6/17/2022
Medically reviewed by Kelly A. Truesdale, DO; Board Certification: Family Practice


Goyal, R. "High-Altitude Pulmonary Edema." Medscape. Nov. 30, 2013. <>.