High altitude illness

High-altitude illness (HAI) encompasses acute mountain sickness, high-altitude pulmonary edema (HAPE), and high-altitude cerebral edema (HACE). These diseases typically occur in lowland residents following an ascent to high altitude.

Although acute mountain sickness is normally a self-limiting disease, it is associated with the development of HACE; HAPE and HACE are often fatal if left untreated.

Descent is the most effective form of treatment for all three conditions.

The diagnosis is usually clinical. However, the combination of a remote and hostile environment together with the potential for other medical conditions sometimes makes confirmation of the diagnosis difficult to achieve.

New symptoms at altitude should be assumed to be those of a high-altitude illness until proven otherwise.

Healthcare providers should counsel international travelers to high-altitude destinations on gradual acclimatization strategies and the use of drugs to prevent altitude illness.

HAI encompasses acute mountain sickness, HAPE, and HACE.[1]Centers for Disease Control and Prevention. CDC Yellow Book 2026: health information for international travel. Section 3: environmental hazards & risks - high altitude travel and altitude illness. Apr 2025 [internet publication]. https://www.cdc.gov/yellow-book/hcp/environmental-hazards-risks/high-altitude-travel-and-altitude-illness.html These diseases typically occur in lowland residents following an ascent to high altitude.