Experts from the University of Edinburgh have shown for the first time that altitude sickness, which is triggered by falling oxygen levels and happens when people reach heights of more than 8202ft, is actually two different illnesses.
It is believed that the research will lead to further work on each individual condition, helping doctors to correctly diagnose patients and then offer the best treatment for them.
Dr Ken Baillie, of the Roslin Institute at Edinburgh University, said: "For more than two decades, we have thought of altitude sickness as a single disease.
"We have now shown that it is at least two separate syndromes that happen to occur in the same people at a similar time.
"Studying these syndromes in isolation will make it easier to understand the cause of each one and to test new treatments."
Altitude sickness is relatively common among climbers who reach certain heights and most cases cause mild symptoms such as headaches, nausea, dizziness and exhaustion.
But in more severe cases it can be life-threatening, causing fluid to build up either on the lungs or the brain.
The researchers used computer analysis to study patterns of symptoms among people in high altitude areas in Bolivia and Tanzania.
The findings, published in the PLOS One journal, will be presented at an international altitude sickness meeting.