At what altitude does extreme hypoxia occur?

Extreme hypoxia occurs at altitudes around 20,000 feet. At this altitude, the partial pressure of oxygen in the atmosphere decreases significantly, leading to inadequate oxygen availability for human physiological needs. This can cause severe impairments in cognitive function, coordination, and overall performance. The body's ability to compensate for the reduced oxygen becomes limited, and symptoms like confusion, shortness of breath, and, in extreme cases, unconsciousness can manifest. While hypoxia can start to affect individuals at lower altitudes, the term "extreme hypoxia" is specifically associated with conditions present around 20,000 feet, where the risks to health increase substantially without supplemental oxygen or cabin pressurization.