Introduction To Altitude Sickness

An Introduction To Altitude Sickness

Altitude sickness (also known as acute mountain sickness) (AMS), is a condition that only develops at high altitudes. It has been a problem of high altitude travelling, in places like the Himalayas, Andes, and some of the mountains in the Rocky mountain Area. The illness can leave people speaking jibberish (see below), out of breath, and eventually slowly into a coma. 

As altitude increases from sea level, the atmospheric pressure decreases, taking oxygen concentration with it. This makes it more difficult to deliver oxygen to your cells. As a result, your body will need to work extra hard to meet its oxygen demands.

This is then pushed even further when you start doing physical activity like climbing or hiking, which increases your body's demand for oxygen further. 

This article will focus on how altitude sickness works, why is can kill you, and tips on supplements and techniques you can use to reduce its effects, or prevent it from happening altogether.


For those looking for an in depth manual on alpinism, including managing and preventing altitude sickness, check out this Book written by a series of high-level alpinists on the topic. 


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Signs & Symptoms

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Altitude Training Masks

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Altitude Sickness Reference By Altitude:


Atmospheric Pressure And Oxygen:

Oxygen represents about 21% of our air content. This doesn't change at altitude, however, the higher up we go, the less pressure there is. This means that the molecules that make up our air (oxygen, nitrogen, and carbon dioxide) become more spaced out and less concentrated than they were at sea level.

With each breath you take, less of these molecules enter the lungs. The oxygen demands of the body however, do not decrease, so in order to deliver this essential element in adequate supply, our body needs to adapt, and work harder to compensate. Your body does this by taking more breaths, and pumping the blood harder and faster through the body.

This can be seen by an increase in heart rate and breathing rates. 


Altitude Sickness Starts Around 1500m Above Sea Level

At 1500m above sea level, most won't feel the effects of altitude, however, some will begin to notice an altered night vision.

As you continue to increase your altitude, these effects will be felt by more and more people, and some will begin to feel a tingling sensation in their fingers and toes. This is usually the first noticeable indication of AMS.

At 2500m, these effects are much more common, and most people will experience at least some degree of altitude sickness.

According to the International Society of Mountain Medicine (ISMM) “The diagnosis of altitude sickness is made when a headache, along with any one or more of the listed symptoms, is present after a recent ascent above 2500 meters”, they list the following symptoms:

  • Loss of appetite
  • Vomiting
  • Fatigue or weakness
  • Dizziness
  • Difficulty sleeping.

Since the rate of ascent, as well as the altitude itself, is directly related to the development of altitude sickness, it's recommended by ISMM to slow your pace from this point forward to around 300-500m/day for your sleeping elevation.

In the day however, it is good practice to ascend higher before descending back to sleeping elevation. This is commonly referred to as acclimatization. It makes traveling past the 3000m mark very slow but is necessary to lower your chances of acquiring the life-threatening HACE or HAPE (more on these below).

Slowing The Rate Of Ascent

300 - 500 meters per day sleeping elevation

By slowing the elevation where the most amount of time is spent, and where the effects of altitude sickness tend to be the worst (sleeping), you can gradually allow your body to acclimatise to the change in altitude as safely as possible. Numerous physiological changes are ocurring in your body to adapt to this, which takes time.

Pushing further up during the day is helpful, but sleeping should not occur more than 500 meters higher each day past the 2500 meter mark.

Resource For Further Reading

1500 m,

This is the point at which some people will begin to experience the effects of altitude sickness. Early symptoms include poor night vision, headaches, and insomnia.


2500 m,

Most people will experience altitude sickness at this altitude if unacclimatised. Symptoms can range from mild to severe depending on the level of adaptation and acclimatisation.


By 5000 m,

Many unacclimatized people will quickly fall unconscious at this elevation, which will then lead to a coma, and eventual death if not given immediate medical attention (oxygen and immediate descent).


The 8000 m Mark... The Death Zone

The 8000 meter mark is aptly named, the "death zone". This is an altitude where no matter how acclimatized you are, the environment is no longer conducive to cellular reproduction and human life. We can survive here, but not for extended amounts of time.

Everest is a whopping 8848m high, so most people who climb this beast require supplemental oxygen when approaching the 8000m mark. Others will require this much sooner than that depending on the individual. 

It's highly recommended by most "altitude sickness authorities" to remain at this height for the shortest amount of time possible. It's possible to climb Everest and other extreme altitude mountains without supplemental oxygen, but will require rigorous acclimatization practices. See here for Ed Viesturs account on his ascent of Everest without supplemental oxygen.


Critical Symptoms Of Altitude Sickness

The symptoms of altitude sickness start small and increase over time, and along with the increase in altitude.

There are 2 serious complications of altitude sickness:

1. High Altitude cerebral Edema (HACE)

This happens when the brain swells and stops functioning properly. This is a serious, life-threatening condition. People experiencing HACE are often confused and may not be aware of the danger they are in.

People will display confused thoughts, and loss of coordination (ataxia), difficulty understanding or speaking, and vision disturbances.

If you notice someone with these effects, make them walk in a straight line and ask them questions regarding who they are, what time or date it is, and what they are doing. This is a very useful set of simple questions used in emergency medicine to determine if the person is confused or not. Ask specific questions to person, place, time, and event. It is crucial to include questions involving all 4 of these concepts, because if different areas of the brain are affected, someone might be able to answer 3 perfectly, but struggle on the one. By not asking for all of these concepts, HACE may go unnoticed for longer. 

If they fail any of these tests, DESCEND IMMEDIATELY to a lower altitude, and if available, apply supplemental oxygen. Fortunately with a speedy descent, people usually recover quickly, and after a few days may re-ascend with caution.


Remember, do not push yourself, fitness level has very little to do with developing altitude sickness, known your body and listen to it. See the chart above to see when your symptoms go from normal to unhealthy and speak up to your fellow alpinists if this happens. 

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Watch this video of a climber experiencing dysphasia caused by HACE. 


2. High Altitude Pulmonary Edema (HAPE)

This is a serious complication from AMS that is classified as a fluid buildup in the lungs. This condition will ultimately result in death if left untreated for too long and is virtually the same cause of death for conditions like pneumonia, only from a different pathology.  

Just like with HACE, if treated promptly by descending to a lower altitude and supplementing oxygen, this condition will usually clear up without issues. It's most common in younger, more fit hikers and climbers, and usually begins during sleep.


The symptoms of HAPE include:

  • Extreme fatigue
  • Breathlessness at rest
  • Fast shallow breathing
  • Cough
  • Pink frothy sputum
  • Gurgling
  • Chest tightness
  • Blue lips/fingernail beds

Treatment Of Altitude Sickness:

Many write off the early effects of altitude sickness as a cold/flu, or simply fatigue from physical exertion. This causes many people to ignore their symptoms and continue pushing further up in elevation. If you continue past these symptoms for too long or push them too hard, serious complications can arise like HACE, ataxia, HAPE, hallucinations, and loss of consciousness which will eventually result in coma and death.

For this reason, if you are above 2500m, and any of these symptoms are present, IT IS MOST LIKELY altitude sickness. Based on the severity of symptoms you should descend and acclimatize further, or push on WITH CAUTION.

It's unwise to ignore serious symptoms, listen to your body. It;s okay to experience some forms of altitude sickness, but it is not okay to ignore it.

In the early signs of AMS, it's recommended that you slow your pace, and allow more time to acclimatize, and keep hydrated. Have a pot of coffeeyerba maté, or some caffiene or vinpocetine tablets and ensure you are taking long deep breaths. 

Supplements For Altitude Sickness

There are numerous supplements available for reducing the effects of altitude sickness, most of which work best if taken for weeks-months building up to the altitude exposure.

These supplements generally work by increasing the hemoglobin counts in the blood gradually (thus more oxygen carrying capacity), increasing cerebral blood flow through vasodilation, or through a number of other mechanisms.

As the symptoms progress, you need to consider reducing your altitude to the last altitude in which you felt healthy in order to avoid the more dangerous side effects.

In the worst case scenario, where someone has encountered pulmonary edema, or cerebral edema, hallucinations, and possible coma, oxygen should be administered IMMEDIATELY, and this person needs to be removed to a lower altitude.

Hyperbaric bags also exist as a way to immediately increase pressure and  oxygen concentration while removing a severely affected individual to a lower altitude.

Fortunately, AMS is generally easy to treat if the treatment is given before serious complications occur.



The best form of medicine in all cases is prevention. By taking some steps, and preparation before subjecting yourself to altitude, you can both reduce its effects, and increase altitude before it's felt in the first place. Prevention consists of acclimatization, and system toning through herbs, supplements, and training techniques. 



Anybody can get altitude sickness. It's not dependent on age, gender, or fitness levels, and resistance is mainly thought to be genetic. Some acclimate very quickly while others take a long time. It's suggested that those with previous experience at altitude will acclimate much faster, especially if within the last 3-6 months.

Acclimatization basically means allowing the body to adapt to the environment of higher altitudes. To do this requires time.

If you live in the rocky mountains, Himalayas, Andes, or any other range with mountains exceeding 2000 meters, a good practice would be to go up the nearest mountain as often as possible, and spend some time at the top. Many athletes try to spend the night at these elevations about once a week or so to maintain their tolerance to these sorts of altitudes.

Basically by doing this you are trying to convince your body to trigger the defensive steps it takes to reduce the effects of a hypoxic environment, AKA high altitude.


Cardio Training

Another option, which can easily be incorporated into a workout routine to prepare for the low oxygen environment, is to use what is called an elevation mask. We recommend this one. 

The idea is to limit the intake of oxygen during a workout. Although this doesn't offer any impact on the oxygen concentration in the air, it can simulate the hypoxic conditions experienced at higher altitudes. This is useful for both mental preparation, as well as cardiovascular preparation, forcing the heart to beat faster to perform the same activities.

Elevation Masks

Another option, which can easily be incorporated into a workout routine to prepare for the low oxygen environment, is to use what is called an elevation mask.

It's important to note that this training won't increase hemoglobin, or train the body for low oxygen concentrations, however, they can strengthen the lungs and increase heart rate during training.

We Recommend This One

Most models come with the ability to change the breathing difficulty using various filters that go into the mask. 


To Summarize:

The golden rule should be; if your above 2500m and you feel sick, ASSUME it's altitude sickness. Know the symptoms, and know when to turn around and descend to a lower elevation for a few days before continuing back up. There may be times where you will have to make that judgment for your partners when they are too confused to make it for themselves, and keep in mind, this might not be as obvious as it seems.

Let us know about your opinions or experiences with altitude sickness in the comment section below, or contact us directly here, we'd love to hear from you.


Justin Cooke

The Sunlight Experiment

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  4. International Society for Mountain Medicine. (2006, January). Non-Physician Altitude Tutorial. Retrieved from