When you’re mountain climbing, hiking, driving, or doing any other activity at a high altitude, your body may not get enough oxygen.

The lack of oxygen can cause altitude sickness. Altitude sickness generally occurs at altitudes of 8,000 feet and above. People who aren’t accustomed to these heights are most vulnerable. Symptoms include headache and insomnia.

You shouldn’t take altitude sickness lightly. The condition can be dangerous. Altitude sickness is impossible to predict — anyone at a high elevation can get it.

The symptoms of altitude sickness can show up immediately or gradually. Symptoms of altitude sickness include:

  • fatigue
  • insomnia
  • headache
  • nausea
  • vomiting
  • rapid heart rate
  • shortness of breath (with or without exertion)

More serious symptoms include:

  • skin discoloration (a change to blue, gray, or pale)
  • confusion
  • coughing
  • coughing up bloody mucus
  • chest tightness
  • decreased consciousness
  • inability to walk in a straight line
  • shortness of breath at rest

Altitude sickness is classified into three groups:


Acute mountain sickness (AMS) is considered the most common form of altitude sickness. The symptoms of AMS are very similar to being intoxicated.


High-altitude cerebral edema (HACE) occurs if acute mountain sickness persists. HACE is a severe form of AMS where the brain swells and stops functioning normally. Symptoms of HACE resemble severe AMS. The most notable symptoms include:

  • extreme drowsiness
  • confusion and irritability
  • trouble walking

If not treated immediately, HACE can cause death.


High-altitude pulmonary edema (HAPE) is a progression of HACE, but it can also occur on its own. Excess fluid builds up in the lungs, making it difficult for them to function normally. Symptoms of HAPE include:

  • increased breathlessness during exertion
  • severe coughing
  • weakness

If HAPE isn’t treated promptly by decreasing altitude or using oxygen, it can lead to death.

If your body doesn’t acclimate to high elevations, you may experience altitude sickness. As altitude increases, the air becomes thinner and less oxygen-saturated. Altitude sickness is most common at elevations above 8,000 feet. Twenty percent of hikers, skiers, and adventurers traveling to high elevations between 8,000 and 18,000 feet experience altitude sickness. The number increases to 50 percent at elevations above 18,000 feet.

You’re at low risk if you’ve had no previous episodes of altitude sickness. Your risk is also low if you gradually increase your altitude. Taking more than two days to climb 8,200 to 9,800 feet can help reduce your risk.

Your risk increases if you have a history of altitude sickness. You’re also at high risk if you ascend rapidly and climb more than 1,600 feet per day.

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Your doctor will ask you a series of questions to look for symptoms of altitude sickness. They’ll also listen to your chest using a stethoscope if you have shortness of breath. Rattling or crackling sounds in your lungs can indicate that there’s fluid in them. This requires prompt treatment. Your doctor may also do a chest X-ray to look for signs of fluid or lung collapse.

Descending immediately can relieve early symptoms of altitude sickness. However, you should seek medical attention if you have advanced symptoms of acute mountain sickness.

The medication acetazolamide can reduce symptoms of altitude sickness and help improve labored breathing. You may also be given the steroid dexamethasone.

Other treatments include a lung inhaler, high blood pressure medication (nifedipine), and a phosphodiesterase inhibitor medication. These help reduce pressure on the arteries in your lungs. A breathing machine may provide assistance if you can’t breathe on your own.

Complications of altitude sickness include:

  • pulmonary edema (fluid in the lungs)
  • brain swelling
  • coma
  • death

People with mild cases of altitude sickness will recover if it’s rapidly treated. Advanced cases of altitude sickness are harder to treat and require emergency care. People in this stage of altitude illness are at risk of coma and death due to brain swelling and the inability to breathe.

Know the symptoms of altitude sickness before you ascend. Never go to a higher altitude to sleep if you’re experiencing symptoms. Descend if symptoms get worse while you’re at rest. Staying well hydrated can decrease your risk for developing altitude sickness. Also, you should minimize or avoid alcohol and caffeine, as both can contribute to dehydration.

Keep reading: Mountain climbing safety »