What Is It?
At higher altitudes, the pressure of the air around you (barometric pressure) decreases so there is less oxygen in surrounding air. People can live comfortably at moderately high altitudes, but the body must make some adjustments, and this takes time. If you ascend to altitudes above 8,000 feet, you will be in danger of developing uncomfortable or dangerous symptoms from the change in altitude.
Symptoms of altitude sickness that are not life threatening are called acute mountain sickness. Mountain climbers on any high mountain and skiers in high-altitude locations such as Colorado are at risk of developing acute mountain sickness. Symptoms from acute mountain sickness improve if you descend to lower altitude quickly. For very mild symptoms, a delay before further climbing may be enough to allow symptoms to go away.