Acute Mountain Sickness (AMS) is an illness that can affect anyone at high altitude, typically above 4300 metres. AMS is brought on by the combination of reduced air pressure and lower oxygen concentrations at high altitudes. At around 5500 metres the oxygen available is less than half than at sea level. Symptoms can range from mild to life-threatening. AMS can involve the nervous system, lungs, muscles, and heart.

In most cases the symptoms are mild. In severe cases, pulmonary edema occurs. This is a condition where fluid collects in the lungs causing breathing shortcomings. The diminished breathing capacity further reduces the oxygen entering the bloodstream, and in turn, reaching the vital organs and tissue. Brain swelling may also occur, this is cerebral edema. This can cause confusion, coma, and when untreated, death.

The chance of getting AMS increases the faster a person ascends. People who normally live at or near sea level are more likely to suffer from AMS. Around 20% will develop mild symptoms at altitudes starting at 2500 metres, however pulmonary or cerebral edema is extremely rare at these heights. Above 4300 metres, almost everyone will suffer mild symptoms, and a few will develop pulmonary or cerebral edema. Above 8000 metres is the death zone. Your body starts to “die” above this altitude. No one can stay unprotected in the “death zone” for very long.



Mild to moderate AMS:
  • Difficulty sleeping,
  • Dizziness or light-headedness,
  • Fatigue,
  • Headache,
  • Loss of appetite,
  • Nausea or vomiting,
  • Rapid pulse,
  • Shortness of breath with exertion.
Severe AMS:
  • Bluish discolouration of the skin,
  • Chest tightness or congestion,
  • Confusion,
  • Cough,
  • Coughing up blood,
  • Decreased consciousness,
  • Withdrawal from social interaction,
  • Grey or pale complexion,
  • Inability to walk in a straight line,
  • Shortness of breath at rest.


The main treatment for all forms of AMS is to descend to a lower altitude.  People with severe AMS will be admitted to a hospital. In mild cases, the symptoms improve very quickly when returned to a lower altitude. Severe cases may result in death from respiratory distress or brain swelling.

The ascent should be slow to allow for acclimatization.

To protect most people from AMS, consider the following:

  • Above 3000 metres altitude – ascent should be slow and gradual,
  • Do not ascend more than 300 metres per day
  • For every 1000 metres above 3000 metres – two nights should be spent at that altitude,
  • Sleep at a lower altitude when possible,
  • Learn how to recognize early symptoms,
  • When above 3,000 metres – carry oxygen,
  • Drink enough fluids,
  • Avoid alcohol,
  • Eat regularly.


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