Altitude Sickness – Symptoms, Prevention, and Treatment

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This post is dedicated to a condition known as altitude sickness, its signs and symptoms, means of prevention as well as proper treatment. There are lots of interesting facts and statistics about altitude illness. For example, it is possible to suffer from altitude sickness only at higher elevations or that anyone can get it regardless of his or her physical condition, age, weight or previous experience in high altitude environments. If you read the whole post, you’d find and more interesting things about altitude illness.

High altitude[1] activities such as hiking and climbing can be very rewarding, however, they can also pose a serious threat to the state of health of anyone practicing them. Most people who have ever gone at altitude know that there are various dangers related to high altitude travel, climbing, and being at higher elevations, in general. Though many of these health risks can be avoided and/or are more or less manageable (for example, you can prevent most heat and UV radiation-related conditions such as sunburn and snow blindness by using effective techniques such as: applying and reapplying sunscreen when necessary, wearing a long sleeve shirt and sunglasses, being properly hydrated, etc.), some hazards such as the so-called altitude sickness stem from the elevation itself thus they cannot be easily avoided.

Altitude illness is a condition associated with travel to elevations above 2500m. Nonetheless, in some cases, symptoms of some forms of altitude sickness can appear at elevations as low as 2000m.

There are three forms of acute altitude illness:

  • Acute mountain sickness (AMS)
  • High altitude pulmonary edema (HAPE)
  • High altitude cerebral edema (HACE)

Traveling to and living at high altitude regions have become more common. This has given clinicians and scientists an opportunity to become more familiar with the various conditions and disorders related to high altitude. As a result, a ton of information is publicly available so that everyone who’s interested in high-altitude travel (or any other high-altitude activity) can become familiar with the symptoms, dangers, and risks associated with these disorders. Such information will help you plan your high-altitude adventure better.

Note that altitude sickness can affect anyone, however, some people just cannot tolerate high altitudes well and are much more likely to develop this disorder. They should know that this has nothing to do with age, physical shape, endurance or lack of character. Moreover, beginners and seasoned backpackers are equally affected by this disorder.

Hiker approaching snow capped mountains

Photo by Dakota Monk

Altitude sickness and acclimatization

The first documented accounts of altitude illness date back to more than 2000 years ago when a Chinese official named Too Kin described the region of the Himalayan Karakoram Pass as “Big Headache Mountain” because of the difficulties experienced by travelers moving across the area. This shows that people have witnessed and known about the effects of traveling at high altitude for thousands of years.

Understanding altitude physiology is an important part of understanding what causes altitude sickness. Among the biggest challenges at higher elevations are thin air and decreased barometric pressure. As a result of these:

  1. There’s less oxygen available to breathe.
  2. The oxygen there is less dense than at low altitudes, which makes it more difficult to breathe and optimize oxygenation.
  3. The body is hard-pressed to get enough oxygen and enters the state of reduced oxygen called hypoxia.

Hence, the body needs to minimize the effects of altitudes and to adapt to these new conditions. The process is called acclimatization. It allows the body to catch up and optimize oxygenation by increasing the efficiency of oxygen use and its transportation to the cells. For example, an increase in respiratory rate can be observed as this usually continues 4-7 days, though some medications such as acetazolamide can alter the duration of this period.

Though altitude illness can affect anyone, people who quickly ascend at high elevations such as backpackers, climbers, and those who fly to a high altitude and proceed directly to a higher area are more likely to experience altitude sickness. Gradual hiking up combined with allowing sufficient rest at various intermediate altitudes will give your body time to adapt and acclimatize better to areas with decreased air pressure. Factors that facilitate acclimatization (other than the rate of ascent) include:

  • Large fluid intake

Drink at least five liters per day to ensure good hydration. One sign of adaptation is a passage of lots of urine – more than a liter per day if possible. The urine color should be almost clear.

  • Rest

Having enough rest helps and accelerates the process of acclimatization. Pacing is important; undue exertion and overexertion should be avoided.

  • High-carbohydrate diet

A diet high in carbohydrates will give you enough energy to hike at altitude. A healthy appetite is a sign of acclimatization. Also, don’t take salt tablets and avoid excessive salt intake, in general.

The amount of time necessary for proper acclimatization is individual and varies greatly not only from individual to individual but also in the same individual over time. Generally, it’s hard to predict how your body will react at higher elevations but it is possible to predict it if you are familiar with your personal adaptive capabilities (usually comes with experience). As acclimatization occurs, all the physiologic alterations and compensatory mechanisms accompanying it such as increased heart rate normalize over time.

Those who aren’t properly acclimated can get one or more of the three forms of altitude sickness. Though there are various symptoms and signs related to these altitude-related disorders, watch out for some of the most obvious signs such as:

  • Loss of appetite
  • Unusual fatigue while walking and difficulty keeping up
  • Breathlessness at rest
  • Resting pulse over 110 per minute

Judgment is affected by altitude so this list should guide you should you suspect that you or someone else has become a victim of altitude sickness.

Altitude Sickness - Symptoms, Prevention, and Treatment: four climbers

Types of altitude illness

Acute mountain sickness

This is the most common form of altitude sickness as it affects up to 50% of those living or traveling at altitude. It usually comes after a day or two at high altitudes, however, the symptoms may begin as early as two hours after arrival to attitude. The main symptom is a persistent headache, usually present on awakening. It is often accompanied by one or more of the following symptoms:

  • Insomnia or frequent awakening during sleep
  • Loss of appetite
  • Dizziness or light-headedness
  • Nausea
  • Vomiting
  • Feeling tired
  • Listlessness

The symptoms of AMS resemble other common conditions such as a case of flu, carbon monoxide poisoning, or a hangover.

Prevention of AMS

The best way to deal with altitude sickness is prevention done through acclimatization to high elevations. After 3000m, try to stick to a controlled, gradual ascent of no more than 500m in vertical elevation gain in sleeping altitude per day followed by a day of no gain in sleeping elevation every three to four days. Many alpinists from all over the world use another technique called “climb high, sleep low” for accelerating acclimatization. Another technique is also popular mainly among alpinists from Russia and East Europe – instead of descending to the base camp for sleeping, they sleep in the camp they have ascended to during the day so that they don’t have to go down and spend the night at the base camp. The risks of using this technique are relatively small even for the not so well-prepared alpinists. Other measures for prevention of AMS include proper hydration, high-carbohydrate diet, and reduction in energy expenditure to a moderate level until you’re acclimated.

The use of some medicines like acetazolamide (you can find it also under trade names such as Diamox, Diacarb, etc.) and dexamethasone (also available under trade names like Decadron, Diodex, Dexasone, etc.) can also prevent and/or deal with altitude-related health problems, though, at really high altitudes, they may not be effective at preventing and treating AMS. In general, acetazolamide also aids acclimatization, while dexamethasone doesn’t facilitate acclimatization. The recommended use of acetazolamide is 125mg twice daily started the day before the ascent and continued through the first 48 hours after that. Keep in mind that this medication causes frequent urination and thus proper hydration is more than desirable. Roughly 6 to 8% will have an allergic reaction so be careful when using it for the following symptoms: nausea, tingling, ringing in the ears, and metallic taste. You can test the effect of acetazolamide at home before going to the mountains. This way you’ll know for sure if you can use it at high altitudes or not. You’ll probably need a prescription from a doctor to buy this medicine. The recommended treatment dose of dexamethasone is 2mg every six hours or 4mg every twelve hours. Recent studies show that ibuprofen (600mg three times daily) may also be used for preventing AMS symptoms, though further research is needed to measure its performance in comparison to acetazolamide and dexamethasone.

Treatment of AMS

The single best treatment option is a descent of 600-900m or more in elevation. If your condition improves upon descent, you’ll know for sure that you’ve been affected by AMS. However, it’s not always necessary to immediately descend as taking a rest day at the current elevation combined with treatment of symptoms can facilitate acclimatization. Both acetazolamide (the treatment dose is 250mg twice a day) and dexamethasone (4mg every six hours) are helpful. Another effective treatment of AMS is the use of oxygen and portable hyperbaric bag (Gamow bag).

It is important to remember that further ascent should be delayed until the symptoms of AMS have been resolved. Then, cautious return to elevation may occur with appropriate acclimatization.

Hiker with altitude sickness near snow capped mountain

Photo by JoJo Chuk

High-altitude pulmonary edema

HAPE is a potentially fatal condition since this form of altitude sickness leads to problems with respiratory function caused by body fluids leaking into the lungs. The most common altitude-associated cause of death, HAPE can occur quite suddenly in people who were otherwise performing well. HAPE (mainly pulmonary problem) is different than AMS and HACE (both are neurological problems), however, in certain cases, it can occur together with HACE (up to 14% will have both) or AMS (up to 50%).

Main signals and symptoms observed in HAPE include:

  • Persistent and sometimes progressive cough (from dry to wet, bloody and frothy in severe cases)
  • Low-grade fever
  • Rapid breathing (tachypnea) and pulse
  • Chest tightness and breathlessness
  • Respiratory crackles
  • Tachycardia (increased heart rate)
  • Blue discoloration of lips
  • Decreasing ability to exercise
  • Falling behind partners

On some occasions, HAPE symptoms coincide with symptoms of pneumonia, however, HAPE worsens rapidly with the continued ascent. Rapid ascent to high altitude, genetic predisposition, pulmonary hypertension, inflammation, and infection are among the most common factors that contribute to the onset and progression of HAPE. In addition, the condition is more likely to affect those who have ever been affected by high-altitude pulmonary edema before.

The incidence of this type of altitude sickness depends also on the elevation as according to Jensen and Vincent:

“At 4500 meters the incidence is 0.6% to 6%, and at 5500 meters the incidence is 2% to 15%, with faster ascent time correlating to a higher incidence. Those with a prior incidence of HAPE have a recurrence rate as high as a 60%.”

Prevention of HAPE

Prevention via staged and gradual ascent is recommended. You can also use nifedipine (30mg Extended-Release every 12 hours) supplemented by salmeterol.

Treatment of HAPE

Survival depends on a rapid response. If caught early, a descent of 900m or more resolves HAPE successfully in nearly all cases. Some temporary treatments include oxygen and Gamow bag, nifedipine and other drugs that widen blood vessels. However, for solving this condition real descent must occur. Don’t delay it because death can be only a few hours away. Keep in mind that nifedipine decreases blood pressure, so it may drop sufficiently making it difficult for those affected to climb down alone. Seriously ill people should be either evacuated or helped by others to descend without exertion. Once the symptoms of this condition have been resolved, reascending is possible.

Man with altitude sickness descending

Immediate descent is critical to survival when having HAPE or HACE

High-altitude cerebral edema

HACE is often a progression of AMS, though it has more severe symptoms and affects only around 1% of all trekkers, travelers, and climbers at altitude. It usually affects people above 3000m, though it can occur at around 2600m too. HACE occurs often in people who have had AMS that’s worsening. It can be fatal since it is caused by leaking of vessels in the brain that leads to swelling of the brain with increased fluid.

On some occasions, HACE can occur after a day or two at altitude; on others, it can occur after several weeks at high elevation. In both cases, however, once developed, it advances rapidly. Main symptoms and signs of this form of altitude illness include:

  • Headache
  • Nausea
  • Throwing up
  • Deteriorating coordination
  • Severe lassitude
  • Altered mental status (confusion, hallucinations, apathy, etc.) followed by coma and death.

Prevention of HACE

As with all kinds of altitude sickness, prevention through gradual ascent and appropriate acclimatization is key. Just as the case with AMS, acetazolamide (125mg twice daily) and dexamethasone (2mg every six hours or 4mg every twelve hours) can be used for prevention.

Treatment of HACE

Immediate descent is critical to survival because death can occur in less than 24 hours of developing ataxia. Supplemental oxygen and Gamow bags can be used for temporary stabilization (these means can be effective for no more than several hours) if descent cannot be done right away. Dexamethasone (initial dose of 8 mg once, then 4 mg every six hours) delivered by mouth or by IM injection can be used for temporary stabilization too. Acetazolamide may aid in acclimatization and prevention of HACE, but it is not an effective treatment strategy for this condition. Don’t leave people with HACE to descend alone and don’t let them sleep at high elevation – this won’t help but may kill them. Once the symptoms of HACE have been resolved, reascending should not be considered.

Table: Recommended medication dosing to prevent and treat altitude sickness

Altitude sickness treatment table

Source: The official Web site of the Centers for Disease Control and Prevention (CDC)


Altitude sickness is no joke but a condition that can be a serious threat for your life. Many trekkers, experienced climbers, and other top athletes have died from this disorder because they have ignored the possibility of having an altitude sickness or have underestimated the severance of their condition. Note that those trekking with groups are more prone to die from altitude illness than those who hike alone. What’s the reason for this? Probably peer pressure since when in a group, most people have a tendency to keep going to not hold the party back instead of descending.

Remember that proper acclimatization is the key to avoiding altitude-related disorders and don’t skip steps during this process and you should be fine. If you have milder symptoms, try to have some rest at that altitude and never ascend to and sleep at higher elevation until better. If you have severe symptoms such as disorientation, confusion, hallucinations, deteriorating coordination, severe lassitude, persistent cough with blood, etc. Descend at the onset of these symptoms without hesitation – if possible to below the altitude where symptoms first occurred – because this may be your only chance to survive.


[1] High altitude is defined as 1500 to 3500m, very high altitude as 3500 to 5500m, and extreme altitude as 5500m and above.


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