Before you fly to Nepal, trek in Machu Picchu, or ski the epic powder of the Utah Rockies, you need to know how to identify, prevent, and treat altitude sickness. Acute mountain sickness (AMS) most often starts above 2500 meters or 8200 feet, but some people feel symptoms well before that. Knowing how to address AMS can save your trip and even your life.
Altitude sickness occurs when your organs don't get enough oxygen at high altitudes, usually above 2500 m.
If you ascend slowly, you'll likely adjust to the altitude with little to no symptoms. Traveling too high too fast puts you at the greatest risk for altitude sickness.
Altitude sickness includes three conditions: acute mountain sickness (AMS), high-altitude cerebral edema (HACE), and high-altitude pulmonary edema (HAPE).
You can prevent and treat all three conditions.
If you experience severe symptoms of AMS or if it progresses to HACE or HAPE, you must descend to a lower altitude.
What is altitude sickness?
Altitude sickness is an acute mountain sickness (AMS) caused by a lack of oxygen to your organs at high altitudes. At first it causes a headache and sluggishness. If ignored, it may progress to dangerous amounts of fluid on your brain or in your lungs.
When you travel from a lower to a higher altitude, your body typically adjusts well if you take it slowly. However, if your body doesn't adjust, you will get altitude sickness which is divided into three syndromes: acute mountain sickness (AMS), high-altitude cerebral edema (HACE), and high-altitude pulmonary edema (HAPE).
Only about 20% of people feel mild symptoms at 2500 m (8200 ft) above sea level. The risk of altitude sickness increases at altitudes above 3000 m (about 9842 ft). 4% of visitors die from HACE or HAPE at elevations higher than 7000 m.
However, death from AMS is preventable. Severe AMS is often caused by progressing too quickly to a high altitude coupled with serious physical exertion, like hiking or climbing swiftly. This fast pace without acclimating first causes your organs to shut down and can deteriorate rapidly to death in as little as two days.
Your body can adjust to high altitude
Usually, people adjust well to lower oxygen levels with adequate time. Progressing slowly from lower to higher levels – also called acclimatizing – allows your body to adapt.
As you travel higher, your heart rate increases, and your breath becomes faster and deeper to increase your oxygen levels. Breathing faster causes you to take in more oxygen, but it also makes you breathe off more carbon dioxide.
As you lose carbon dioxide, your blood becomes more alkaline – or less acidic. This imbalance makes your body work to restore your normal acid-base balance. It does this by slowing your breathing, mostly at night, and making you urinate more to reduce alkalinity.
This is a normal process that takes a few days. You feel breathless when you exert yourself. You may wake at night feeling like you need more air.
You won't feel great, but it doesn't mean you have AMS. If you remain at that elevation for a few days, stay hydrated, and don't overexert yourself, you'll likely feel better in 2–5 days.
Symptoms of altitude sickness
There are distinct symptoms for each type of altitude sickness. It's important to know what to look out for.
Acute mountain sickness (AMS)
AMS is the first and most common condition. It causes a collection of signs telling you your brain requires more oxygen. When you're at a high altitude, it's important to consider AMS whenever you or a traveling partner feels sick. AMS can worsen fast, so you must be ready to identify and treat altitude sickness when you see it.
- Headache. Since the brain is the most sensitive organ to oxygen stress, it triggers AMS symptoms, usually within 2–12 hours of arriving at higher altitudes. A headache is the classic first symptom. Similar to a hangover, you may also feel fatigued, nausea, a loss of appetite, and have sleeping difficulties.
- Pale skin and irritability. Since children and adults are equally susceptible to AMS, your child may show these signs along with increased irritability and pale skin.
If your symptoms remain mild, you’ll acclimatize within a few days. If your symptoms worsen, you need to head to a lower altitude.
Whatever you do, don't travel higher if you have AMS symptoms. Doing so rapidly increases your chances of HACE, HAPE, or both.
High-altitude eerebral Edema (HACE)
HACE is a rare but life-threatening progression of AMS caused by brain swelling. As the leading cause of death in failed attempts to summit Mount Everest, HACE requires immediate descent to a lower altitude.
In a low-oxygen state, your blood vessels become leaky, causing fluid to accumulate (known as edema) in the brain or lungs.
Fluid on the brain causes the signs and symptoms of HACE, including increased neurological signs like unsteadiness, confusion, slurred speech, clumsiness, aggression, drowsiness, and social withdrawal.
Without immediate help, someone with HACE will lose consciousness and die, even within 24 hours.
High altitude pulmonary edema (HAPE)
HAPE, which often happens along with HACE, occurs when fluid accumulates in your lungs, causing pulmonary symptoms.
Signs and symptoms of HAPE often start when you sleep, causing a sharp increase in breathing difficulty. Symptoms include:
- Extreme fatigue
- Rattling or gurgling breath
- A moist cough sometimes with pink, frothy sputum
- Fast heartbeat
- Blue lips, toes, and fingers
What causes altitude sickness?
At sea level, the weight of the atmosphere is heavy, which increases air pressure. This weight moves oxygen molecules closer together, allowing you to breathe in more molecules with each breath.
As you travel to higher elevations, the atmosphere becomes lighter. This lower pressure — or "thinner" air — spreads out the molecules, causing you to breathe in fewer with each breath. According to the Centers for Disease Control and Prevention, the oxygen you breathe at 3000 meters (10,000 feet) is 69% of what you get at sea level.
No matter how high or low you travel, the air is mainly comprised of five gases:
- Water vapor
- Carbon dioxide
In general, oxygen molecules make up 21% of these gases, whether you're at sea level or on Mount Everest.
Even though the percentage of oxygen remains the same, your body gets less and less as you travel higher and higher.
Who's at risk for AMS?
It's hard to predict who will feel sick at high altitudes. Physical fitness doesn't lower your risk, nor does age for the most part. Individuals over age 50 may be at a slightly higher risk. People with more experience at high altitudes are less in danger, but some still report getting AMS despite several previous high-altitude trips.
Research does reveal a few risks factors including:
- Heart and lungs. Poor cardiac or respiratory health.
- Preexisting conditions. Diabetes.
- Tobacco and alcohol. Drinking alcohol and smoking at high elevations.
- Water. Dehydration.
- Gender. Men are at higher risk than women.
- Genetics. Scientists also believe genetics can make you more susceptible to AMS.
If you've had altitude sickness on a previous trip to high altitudes, you are at a greater risk of experiencing it again. You should see your doctor before traveling to high elevations.
Pregnancy doesn't seem to make you more susceptible, but avoiding high-altitude travel is wise, especially when you're far from medical care. Pregnant women with anemia or any other condition that reduces oxygen supply to the fetus should be extra careful to avoid traveling to high elevations.
In general, everyone increases their risk of AMS when they travel too high too fast with serious physical exertion.
8 tips for preventing altitude sickness
The goal isn't to avoid all AMS symptoms when you travel. Instead, you may have to settle for a mild, manageable illness.
Here are some tips on how to avoid serious altitude sickness on your vacation.
- According to the CDC, aim to travel from a low elevation to no higher than 2750 m (9000 ft) at first. After a day at 2750 m, move your sleeping elevation no higher than 500 m per day. You can trek or drive higher during the day. Lastly, for every 1000 m, plan an extra day to acclimate before moving higher.
- Try to rest for the first 48 hours.
- Stay well-hydrated with water, but don't overdo it. Drink enough water to keep your urine the light color of champagne or straw. When your urine is yellow, you're dehydrated.
- Avoid alcohol for the first 48 hours but continue your normal caffeine intake.
- Data shows that vitamin B6 can be effective in preventing nausea. Consider starting it a few days before traveling.
- For some trekkers and climbers, chewing coca leaves or drinking coca tea may prevent altitude sickness.
- Ibuprofen helps prevent AMS in some travelers. The CDC reports that taking 600mg every 8 hours can help prevent altitude sickness.
- Studies show, however, that acetazolamide (Diamox) is better than ibuprofen. For Diamox to be effective, start taking it 1–2 days before traveling to high elevations. A pediatrician may also prescribe it safely for your child. Scientists aren't positive why Diamox works, but it likely helps the body maintain its acid-base balance. Diamox does have side effects. You may feel an unpleasant tingling in your fingers and feet. Like your body’s natural response to high altitudes, Diamox also increases urination, boosting your chance of dehydration.
Treatment for altitude sickness
The number one treatment for AMS, HACE, and HAPE is to descend to a lower altitude, often triggering immediate relief after dropping 300 m.
However, many people with mild to moderate AMS can safely remain at their current elevation and treat their symptoms.
For a headache due to altitude sickness, doctors recommend ibuprofen because it helps reduce brain swelling. Diamox can also treat AMS symptoms, but it works better for prevention before symptoms start.
Some people also carry ondansetron (Zofran) for nausea. Others try natural remedies like ginger or chamomile tea or digestive bitters. Some people feel relief from rubbing peppermint, lemon, or cannabis essential oil on the back of their necks and the bottoms of their feet. You can also place several drops of the oil on a cool compress and drape it over your forehead.
For those who have access to dexamethasone, a steroid, it rapidly relieves moderate to severe AMS. When available, supplemental oxygen can also treat AMS, possibly saving a traveler from having to descend.
If symptoms worsen, you must head to a lower elevation to reduce your cerebral or pulmonary edema risk using as little physical effort as possible.
For those who develop HACE or HAPE and can’t descend quickly, oxygen and a hyperbaric chamber are lifesaving when available.
Know before you go
You may not be able to prevent altitude sickness altogether, but you can avoid death or evacuation from your long-awaited mountain trip. Since AMS is predictable and easy to identify, it's possible to prevent and treat the condition by adequately preparing before travel.
- Centers for Disease Control and Prevention. CDC Yellow Book, Chapter 3 High-Altitude Travel & Altitude Illness.
- Wilderness and Environmental Medicine. Wilderness Medical Society Clinical Practice Guidelines for the Prevention and Treatment of Acute Altitude Illness: 2019 Update.
- StatPearls. Acute Mountain Sickness.
- Sports Medicine and Health Science. High-altitude illnesses: Old stories and new insights into the pathophysiology, treatment and prevention.