Altitude sickness: What is it, what does it do?

Altitude sickness happens when you’re climbing a mountain, and you ascend above about 8,000 feet – or about 2,400 meters. People with altitude sickness feel tired and nauseated – have a headache – and may feel strangely uneasy.

Lack of oxygen is what causes altitude sickness. As you climb to higher elevations, the air pressure decreases. You take in fewer molecules of air – and thus less oxygen – with each breath. The faster and higher you climb, the greater your risk.

In severe cases, altitude sickness can kill you. Several of the early hot-air balloonists died of altitude sickness. Today, air is pumped into the cabin of passenger planes so we don’t get sick.

In a healthy person at sea level, blood is 99 percent saturated with oxygen. When you’re up at 18,000 feet elevation – or about 5,500 meters – your blood carries about thirty percent less oxygen than it does at sea level.

Still, some people get altitude sickness, and others don’t. No one knows exactly why. If you’re like most people, if you ascend gradually and take it easy, you can become acclimated to the thin air. And, over time, it’s possible for your body to undergo changes to use oxygen more efficiently.

But your immunity to altitude sickness doesn’t last when you descend. About two weeks back at sea level – and those adaptations are almost gone.