Altitude Sickness
Symptoms that arise when the body cannot adjust quickly to high elevations
Quick Facts
- Type: Environmental illness
- Cause: Reduced oxygen at high elevation
- Typical onset: Usually above 8,000 ft (2,500 m)
- Severe forms: HAPE (lungs) and HACE (brain) are emergencies
Overview
Altitude sickness, also called acute mountain sickness, develops when a person ascends to a high elevation faster than their body can adapt. At higher altitudes the air pressure is lower and each breath delivers less oxygen, which can cause a range of symptoms. It commonly affects hikers, skiers, and travelers who go quickly above roughly 8,000 feet (2,500 meters).
Most cases are mild and improve with rest and time to adjust. However, two severe forms, high-altitude pulmonary edema (fluid in the lungs) and high-altitude cerebral edema (swelling of the brain), are life-threatening and require immediate descent and emergency care.
Symptoms
Mild altitude sickness often feels like a hangover and usually starts within a few hours to a day of arriving at altitude.
- Headache, often the first and most prominent symptom
- Nausea, loss of appetite, or vomiting
- Dizziness or lightheadedness
- Fatigue and weakness
- Trouble sleeping
- Shortness of breath with exertion
Warning signs of severe illness include: a cough with frothy or pink spit, breathlessness at rest, confusion, trouble walking in a straight line, severe headache that does not improve, and unusual drowsiness. These are emergencies.
Causes
Altitude sickness is caused by the lower oxygen levels found at higher elevations. When you climb too quickly, your body does not have time to make the gradual changes it needs to cope with thinner air.
The main driver is the rate of ascent rather than how fit you are. Climbing high and sleeping high too soon, heavy exertion before adjusting, and dehydration all make symptoms more likely. The exact way reduced oxygen leads to fluid shifts in the brain and lungs is complex and not fully understood.
Risk Factors
- Rapid ascent to high altitude
- Living at or near sea level before traveling
- A previous episode of altitude sickness
- Heavy physical exertion soon after arriving
- Certain heart or lung conditions
- Dehydration and alcohol use at altitude
- Flying or driving directly to a high-altitude destination
Diagnosis
Altitude sickness is usually diagnosed from the symptoms and the recent history of going to a high elevation. There is no specific test for the mild form.
- Symptom review: a headache plus other symptoms after a recent ascent strongly suggests altitude sickness
- Physical exam: listening to the lungs and checking coordination and alertness to look for severe forms
- Oxygen level: a pulse oximeter may show low oxygen, though readings are normally lower at altitude
- Imaging: a chest X-ray may be used in a medical setting if pulmonary edema is suspected
Treatment
The most important treatment is to stop going higher and let the body adjust.
- Rest and acclimatize: stay at the current altitude and do not climb higher until symptoms ease
- Descend: if symptoms worsen or do not improve, go down to a lower elevation; descent is the single most effective treatment
- Hydration and pain relief: drink fluids and use simple pain relievers for headache
- Oxygen: supplemental oxygen relieves symptoms when available
- Medications: drugs such as acetazolamide can help the body adjust and may be used for prevention or treatment under medical guidance
Severe forms (HAPE and HACE) require immediate descent, emergency oxygen, and specific medications, and can be fatal if not treated quickly. A common guideline for any altitude illness is to stop ascending if you feel unwell, descend if symptoms get worse, and never leave someone with worsening symptoms alone. Even a descent of a few hundred to a thousand meters often brings rapid improvement.
Prevention
- Ascend slowly and allow your body time to adjust
- Once high, avoid increasing your sleeping altitude too quickly each day
- Take a rest day if you feel unwell, and do not climb higher with symptoms
- Stay well hydrated and avoid alcohol on arrival
- Ask a doctor about preventive medication for fast ascents or a history of altitude sickness
When to See a Doctor
Seek help if mild symptoms do not improve with rest or get worse. Descend and seek emergency care immediately for:
- Shortness of breath while resting or a cough with pink, frothy spit
- Confusion, drowsiness, or trouble staying awake
- Difficulty walking straight or loss of coordination
- A severe headache that does not respond to medicine
These signs point to fluid in the lungs or swelling of the brain, both of which can be fatal without rapid treatment.
Frequently Asked Questions
At what altitude does altitude sickness start?
Symptoms most often begin above about 8,000 feet (2,500 meters), though some people feel effects a bit lower. The faster you ascend and the higher you sleep, the more likely symptoms become.
How do I prevent altitude sickness?
Ascend slowly, avoid large jumps in your sleeping altitude each day, stay hydrated, and avoid alcohol when you first arrive. If you have had it before or must ascend quickly, ask a doctor about preventive medication such as acetazolamide.
When is altitude sickness an emergency?
It is an emergency if you have breathlessness at rest, a cough with frothy or pink spit, confusion, severe drowsiness, or trouble walking straight. These can signal fluid in the lungs or brain swelling, and you should descend and get emergency care immediately.
Does being physically fit protect me?
No. Fitness does not prevent altitude sickness, and very fit people sometimes push too hard and get sick. The most important factor is how quickly you ascend, not your fitness level.
How is altitude sickness treated?
Mild cases improve by stopping the climb, resting, drinking fluids, and using simple pain relief. If symptoms worsen, the best treatment is to descend to a lower elevation. Oxygen and certain medications can also help.
References
- Centers for Disease Control and Prevention (CDC). High Altitude Travel and Altitude Illness.
- Mayo Clinic. Altitude sickness.
- MedlinePlus, U.S. National Library of Medicine. Acute mountain sickness.
- Wilderness Medical Society. Acute Altitude Illness.