At what altitude can hypoxia occur?

Hypoxia, the deficiency in the amount of oxygen reaching the tissues, can occur at various altitudes due to the decreasing atmospheric pressure and the corresponding decrease in the partial pressure of oxygen as altitude increases. While it is commonly recognized that significant risks of hypoxia arise at altitudes above 5,000 feet, particularly noticeable at 10,000 feet MSL or higher where oxygen consumption is greatly affected, individuals may experience hypoxic symptoms even at lower altitudes, especially depending on personal factors such as physical condition, acclimatization, and pre-existing health issues.

Circumstances such as exertion, cabin pressure failures, or latent health conditions can exacerbate the potential for hypoxia at any altitude. Therefore, understanding that hypoxia can technically manifest at any elevation underscores the importance of monitoring physical symptoms and environmental factors throughout flight operations, regardless of altitude.