Altitude sickness (mountain sickness)

Altitude sickness (mountain sickness) is an illness that ranges from a mild headache and weariness to a life-threatening build-up of fluid in the lungs or brain at high altitudes.

Acute altitude sickness is the mildest and most common form. Because more people are traveling to areas of high elevation for skiing and mountain climbing, acute altitude sickness has become a greater public health concern. Roughly one fourth of Colorado ski area vacationers, two thirds of climbers on Mount Rainier, and half the people who fly to the Khumbu region of Nepal develop acute altitude sickness.