The main reason why trekkers fail to climb Mt. Kilimanjaro is due to altitude sickness. This sickness is a person’s body’s response to the low oxygen content within the surrounding. Although oxygen is not required for Kilimanjaro climb, supplemental oxygen may be needed on the summit attempt is a person is hit by altitude sickness caused by the lack of oxygen. However, unnecessary use of supplemental oxygen may pose a grave health risk. Supplementary oxygen is normally used if a person suffers from altitude sickness at extreme elevations above 23,000 feet.