The question of experiencing altitude sickness on a commercial flight is common. Altitude sickness, medically known as Acute Mountain Sickness (AMS), results from a rapid ascent to high elevation where the air contains less oxygen. While severe AMS is extremely rare during air travel, the controlled cabin environment simulates a mild altitude. This simulated environment can affect sensitive individuals, causing discomfort that mimics the initial stages of true altitude sickness.
Understanding True Altitude Sickness
True altitude sickness occurs due to hypobaric hypoxia, where both barometric pressure and the partial pressure of oxygen drop significantly. This reduction means less oxygen enters the bloodstream with every breath, challenging the body’s ability to function normally. Symptoms commonly include a persistent headache, nausea, vomiting, fatigue, and dizziness. True AMS typically appears in unacclimatized individuals who ascend rapidly above 8,000 feet (2,400 meters). The condition worsens if the ascent continues without a period of rest and acclimatization.
The Reality of Cabin Pressurization
Commercial aircraft cruise between 30,000 and 40,000 feet, where outside air pressure is too low for human survival. The cabin is pressurized to simulate an altitude, typically maintained at 8,000 feet above sea level, though newer jets often simulate 5,000 to 7,500 feet. This simulated altitude causes a drop in the partial pressure of oxygen available to passengers. For a healthy person, arterial oxygen saturation (SpO2) drops from 97-98% at sea level to around 90-94% during flight. This mild hypoxia is generally well-tolerated.
Sensitive Travelers and Hypoxia
Individuals with pre-existing cardiopulmonary conditions (e.g., COPD or heart conditions) may experience a more significant drop in SpO2. This stress can trigger symptoms similar to mild altitude sickness, sometimes requiring supplemental oxygen. The combination of sustained mild hypoxia and the body’s compensatory mechanisms is the closest a passenger gets to experiencing altitude sickness in a plane.
Symptoms Mistaken for Altitude Sickness
While mild hypoxia can occur, many common discomforts experienced during a flight that resemble altitude sickness are caused by other factors. One major contributor is barotrauma, which is pain caused by expanding gases trapped within the body’s cavities. As cabin pressure changes during ascent and descent, air in the middle ear and sinuses expands, leading to pain, pressure, or a sharp headache.
Environmental Factors
Another significant factor is the extremely low cabin humidity, typically ranging between 10 and 20%. This dry air causes irritation in the nasal passages and throat, contributing to fatigue and general malaise. Low humidity can also compound feelings of lightheadedness or headache, especially if the traveler is not drinking enough fluids.
Travel Fatigue
Restricted movement and general travel fatigue are also frequently mistaken for the lethargy associated with AMS. Prolonged immobility in a cramped seat leads to muscle stiffness and discomfort, often exacerbated by disrupted sleep patterns and travel stress. These non-hypoxic factors combine to create symptoms that mimic the mild effects of true altitude sickness.