IAMAT |International Association of Medical Assistance to Travellers| IAMAT |International Association of Medical Assistance to Travellers|

Altitude Illness

Photo By: William Dixon

Altitude Illness occurs as a result of decreased oxygen pressure at high altitudes. The illness is divided into three syndromes recognized by a cluster of symptoms arising from rapid ascent to high altitudes, especially more than 2400m / 7874ft.


Altitude Illness can occur to anyone at any time regardless of physical fitness. All non-acclimatized travellers, including children, are potentially at risk of developing altitude illness which depends on level of exertion, speed of ascent, altitude reached, humidity, oxygen, and air pressure levels, as well as personal susceptibility. The human body is able to acclimatize to high altitude but must be given time to do so, ideally 3 to 5 days.

Acclimatizing to high altitudes:


The first syndrome, Acute Mountain Sickness (AMS), is characterized by headache, fatigue, loss of appetite, nausea and sometimes vomiting, dizziness, insomnia and disturbed sleep appearing 2 to 12 hours after arrival at high altitude. Symptoms usually disappear within 24 to 72 hours as the body acclimatizes to the altitude. If AMS symptoms persist, rest and acclimatization medication is needed. Do not continue to ascend to a higher altitude if symptoms persist. If there is no improvement descend to a lower altitude, by at least 300m / 984ft.

In rare cases AMS progresses to the second syndrome, High Altitude Cerebral Edema (HACE), which is characterized by worsening AMS symptoms, drowsiness, confusion, staggering gate and ataxia (lack of voluntary muscle coordination). Immediate descent to lower altitude is important since developing HACE symptoms can be life threatening if untreated immediately. HACE is rare at altitudes below 3600m / 11811ft.

The third syndrome, High Altitude Pulmonary Edema (HAPE), affects the lungs and is characterized by increased breathlessness with exertion progressing to breathlessness during rest, a dry cough, chest tightness or congestion, rapid heart beat, general weakness, and blue / purple skin tissue coloration. Developing HAPE symptoms can be life threatening if untreated. Immediate descent to a lower altitude and administration of oxygen are imperative.

Immediate descent, combined with medication (and oxygen, if available), is the best treatment for severe AMS, HACE, or HAPE. Consider evacuation if necessary.


Information last updated: January 2020

Risk of Altitude Illness is present in the following countries:

Travel Health Journal