Why Does Acute Mountain Sickness (AMS) Occur?

If you are climbing Kilimanjaro, you should be aware of a condition called Acute Mountain Sickness, or AMS.

AMS occurs when the human body reacts negatively to high altitude due to a lack of oxygen. High altitude is defined as an altitude greater than 5,000 feet. At both sea level and high elevation, the oxygen percentage does not change – it comprises approximately 21 percent of the air.

However, at high altitude the air pressure is lower and thus there are less gases overall. The number of oxygen molecules decreases. On the summit of Kilimanjaro, there is only about half the oxygen found at sea level.

This shortage of oxygen leads to our body’s physiological response. We compensate by breathing faster and deeper. We produce more red blood cells which carry oxygen around the body. The process continues as we adjust to the atmospheric conditions – a process known as acclimatization.

When our bodies struggle to adjust to the elevation, we develop symptoms of AMS. Some early symptoms include a headache, nausea, shortness of breath and a general feeling of malaise. AMS is typically the result of ascending too quickly, which is why it is preferable to take slower routes to the top and to walk at a deliberately slow pace.

AMS is common, yet unpredictable. It is hard to know who will or will not be stricken with AMS until they are actually at high altitude. Interestingly, a good level of physical fitness does not appear to have much of a correlation with the ability to acclimatize better. Genetics seems to play a main role.

Who is at Risk for Acute Mountain Sickness?

Your risk of experiencing acute mountain sickness is greater if the following factors apply:

  • live by or near the sea/unaccustomed to high altitudes
  • gain elevation quickly at high altitudes
  • exert yourself physically at high altitudes
  • have a low red blood cell count due to anemia
  • have heart or lung disease
  • take medications like sleeping pills, narcotic pain relievers, or tranquilizers that can lower your breathing rate
  • have had past bouts of AMS

In general, any illness at altitude should be presumed to be AMS. On the mountain, our professional guides will monitor you throughout the climb. We implement daily health checks to make sure our clients are able to climb as safely as possible, though risks always remain as AMS can develop and worsen quickly.

Treatment for acute mountain sickness varies depending on its severity. The most effective treatment is to simply descend to a lower altitude. Hospitalization is necessary if you have brain swelling or fluid in your lungs, conditions known as High Altitude Cerebral Edema (HACE) and High Altitude Pulmonary Edema (HAPE).

You may receive oxygen on the mountain also. Our teams carry emergency oxygen and a portable stretcher on every trip in case a rescue is necessary.

Read more about AMS and Ultimate Kilimanjaro’s safety precautions here.


See Should I Use Supplemental Oxygen to Climb Kilimanjaro? 

See Diamox: Does it Mask AMS?

See Are You Afraid of High Altitude?

See Can Training with an Altitude Mask Help Me Climb Kilimanjaro?

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