'Altitude sickness’ is caused at high altitude due to

Altitude sickness, also known as acute mountain sickness (AMS), is primarily caused by hypobaric hypoxia at high elevations [3]. As altitude increases, the total atmospheric pressure decreases [3]. Although the percentage of oxygen in the air remains constant at approximately 21%, the reduction in total barometric pressure leads to a corresponding decrease in the partial pressure of oxygen (PO2). At high altitudes, this low partial pressure of oxygen means there is less oxygen available for the lungs to absorb, leading to reduced arterial oxygen saturation [2]. This hypoxic stress triggers physiological responses like hyperventilation to compensate for the lack of oxygen [1]. If the body fails to adapt to this low partial pressure, symptoms such as breathlessness, dizziness, and fatigue occur, potentially progressing to more severe conditions like cerebral or pulmonary edema [2].

Sources

1. [3] Exploring Society:India and Beyond ,Social Science-Class VII . NCERT(Revised ed 2025) > Chapter 2: Understanding the Weather > c) Atmospheric pressure > p. 34
2. [2] https://www.cdc.gov/yellow-book/hcp/environmental-hazards-risks/high-altitude-travel-and-altitude-illness.html
3. [1] https://www.ncbi.nlm.nih.gov/books/NBK430716/