Editing Altitude sickness (section)

=== Extreme altitude ===
Above {{convert|5500|m|ft}}, marked hypoxemia, [[hypocapnia]], and [[alkalosis]] are characteristic of extreme altitudes. Progressive deterioration of physiologic function eventually outstrips acclimatization. As a result, [[List of highest settlements|no permanent human habitation occurs above {{convert|6000|m}}]]. A period of acclimatization is necessary when ascending to extreme altitude; abrupt ascent without supplemental oxygen for other than brief exposures invites severe altitude sickness.<ref name="Auerbach 2007"/>