There is 66 percent less oxygen in each breath on the summit of Everest than at sea level and while oxygen is used to support climbers, even trekkers visiting Base Camp can experience the breathlessness and headaches associated with Acute Mountain Sickness.
Acclimatising is key. There is 66 percent less oxygen in each breath on the summit of Everest than at sea level and while oxygen is used to support climbers, even trekkers visiting Base Camp can experience the breathlessness and headaches associated with Acute Mountain Sickness. This can kick in anywhere from around 2,400m altitude; Everest Base Camp is more than twice that.