What is a common cause of hypoxia at high altitudes?

Reduced barometric pressure at altitude is the primary cause of hypoxia. As altitude increases, the atmospheric pressure decreases, which in turn results in a reduction in the partial pressure of oxygen available in the air. This lower pressure means that even though the percentage of oxygen in the atmosphere remains constant (around 21%), the amount of oxygen that can enter the bloodstream diminishes. This insufficient oxygen intake can lead to the symptoms of hypoxia, such as dizziness, confusion, and impaired cognitive and physical performance.

Understanding this principle is crucial for pilots, as they must recognize the risks of flying at high altitudes and the need for supplemental oxygen to prevent hypoxia. While the other options touch upon aspects related to altitude, they do not directly address the main factor contributing to hypoxia in a clear and definitive manner.