Merck Manual

Please confirm that you are not located inside the Russian Federation

honeypot link
Quick Facts

Altitude Sickness

By

The Manual's Editorial Staff

Last full review/revision May 2021| Content last modified May 2021
Click here for the Professional Version
Get the full details

What is altitude sickness?

Altitude is the distance above sea level. As you go to higher altitudes, the air contains less oxygen.

Altitude sickness happens when you're at a height with less oxygen than you're used to. For many people this happens above 8,000 feet (2400 meters). Some people can go to much higher altitudes without getting symptoms.

  • The higher you go and the quicker you get there, the more likely you are to get altitude sickness

  • Most people just get headache, tiredness, an upset stomach, and trouble sleeping

  • Some people get a dangerous swelling of their brain or fluid buildup in their lungs

  • You treat altitude sickness by going down to a lower altitude

  • You can prevent altitude sickness by taking your time going up in altitude

  • Certain medicines also can help prevent altitude sickness

What are the types of altitude sickness?

There are 3 types of altitude sickness:

  • Acute mountain sickness: The mildest type of altitude sickness, with symptoms that usually last 1 or 2 days

  • High-altitude cerebral edema (HACE): An uncommon and sometimes fatal medical emergency that causes brain swelling

  • High-altitude pulmonary edema (HAPE): A severe and sometimes fatal medical emergency that causes breathing problems and fluid to fill your lungs

What causes altitude sickness?

Altitude sickness is caused by traveling to a high altitude where the air you breathe contains less oxygen. You have a greater chance of having symptoms if you travel to a higher altitude too quickly or if you sleep at a high altitude.

You're at increased risk for altitude sickness if:

  • You've had it before

  • You normally live at a very low altitude

  • You push yourself too hard (overexert)

Medical problems such as asthma, COPD, and heart disease are NOT risk factors for altitude sickness. However, if you have a serious medical disorder, low oxygen levels at a high altitude can be dangerous.

What are the symptoms of altitude sickness?

Symptoms depend on what type of altitude sickness you have.

With acute mountain sickness, within 6 to 10 hours of traveling to over 8,000 feet you may have:

  • Headache

  • Light-headedness

  • Loss of appetite, upset stomach, or throwing up

  • Feeling tired, weak, or cranky

  • Trouble sleeping

Sometimes people mistake these symptoms for a hangover, migraine, extreme tiredness, or a viral infection.

HACE causes brain swelling that can cause:

  • Headache

  • Confusion

  • Walking that is unsteady and clumsy

If not treated quickly, HACE can cause seizures, coma, and death.

HAPE may happen 24 to 96 hours after you travel quickly to a high altitude. Symptoms are worse at night when you lie down and may become more severe very quickly. HAPE causes lung problems such as:

  • Dry cough and shortness of breath after mild activity

  • Shortness of breath while resting

  • A bluish color in your skin, lips, and nails

  • Sometimes gasping for breath, coughing up pink or bloody mucus, and making gurgling sounds while breathing

If not treated quickly, HAPE can be fatal.

People who live at high altitudes may get HAPE when they return home after a brief stay at a lower altitude (this is called re-entry pulmonary edema).

Even if you don't have one of these types of altitude sickness, you may have symptoms from being at a high altitude such as:

  • Swelling of your hands, feet, and face—this is common and usually goes away in a few days

  • Headache, without other symptoms of acute mountain sickness

  • Small areas of bleeding in the back of the eye (retinal hemorrhages), after traveling above 9,000 feet

Retinal hemorrhages may sometimes cause a small blind spot in your vision, but the blind spot usually goes away after you travel to a lower altitude.

How can doctors tell if I have altitude sickness?

Doctors tell if you have altitude sickness based on your symptoms. They may also:

  • Listen to your chest with a stethoscope to see if you have fluid in your lungs

  • Do an x-ray of your chest

  • Test the amount of oxygen in your blood

How do doctors treat altitude sickness?

Treatment depends on your symptoms and what type of altitude sickness you have. The best first step in treatment for all types of altitude sickness is:

  • Going to a lower altitude

For mild symptoms, doctors will have you:

  • Rest

  • Avoid going to a higher altitude until symptoms disappear

  • Drink lots of fluids

  • Take medicines such as ibuprofen or acetaminophen for headache

For severe acute mountain sickness, doctors will:

  • Have you travel to a lower altitude

  • Give you extra oxygen

  • Have you take altitude medicine such as acetazolamide or dexamethasone

If symptoms are severe, and if traveling to a lower altitude isn't possible, doctors sometimes have you breathe pure oxygen while lying in a special high-pressure bag (hyperbaric oxygen therapy).

How can I prevent altitude sickness?

The best way to prevent altitude sickness is to travel to higher altitudes slowly so your body has time to adjust. The altitude at which you sleep has the greatest effect on you.

Being physically fit doesn't protect you from getting altitude sickness.

Most people easily adjust to altitudes of up to 8,000 feet (2,400 meters) without special precautions. But adjusting to higher altitudes, especially above 10,000 feet (3,000 meters), can take many days or weeks. To go to that height, climbers should only increase their sleeping altitude by about 500 to 1500 feet (300 or 500 meters) a day and should take a day off from climbing higher every 3 or 4 days.

Other ways to prevent altitude sickness:

  • Before you travel, ask your doctor about taking altitude medicines

  • Avoid heavy activity when you arrive at a high altitude location

  • Don't use alcohol, opioids, or sleep medicine

If you’ve had altitude sickness before, watch for signs you’re getting it again and travel to a lower altitude if needed.

NOTE: This is the Consumer Version. DOCTORS: Click here for the Professional Version
Click here for the Professional Version
Others also read

Also of Interest

Download the Manuals App iOS ANDROID
Download the Manuals App iOS ANDROID
Download the Manuals App iOS ANDROID
TOP