Rapid ascents can lead to altitude sickness. The best (and very effective) cure is to descend immediately. The climber's motto in high altitude is "climb high, sleep low", referring to the regiment of climbing higher to acclimitize but returning to lower elevation to sleep. An alternative, traditionally used in South America is the chewing of coca leaves.
Lack of oxygen can start to be a problem for many people at heights below 5,000 m. Everyone needs to acclimatise, even those who can summit Everest without bottled oxygen. Generally speaking, experienced mountaineers do not normally start using bottled oxygen until they reach around 7,000 - 8,000 m.
In 2005, researcher and mountaineer John Semple established that above-average ozone concentrations on the Tibetan plateau may pose an additional risk to climbers.
