The short answer to whether a person can experience altitude sickness while flying is that true Acute Mountain Sickness is exceptionally uncommon in a commercial aircraft. Pressurized cabins are engineered to maintain an internal environment that prevents the severe physiological stress associated with high-altitude exposure. However, the unique atmospheric conditions inside the plane can cause mild symptoms that mimic the general discomfort of altitude sickness, primarily due to a slight reduction in available oxygen.
How Commercial Aircraft Pressurize the Cabin
Commercial airliners typically fly at altitudes between 30,000 and 40,000 feet, where the natural atmospheric pressure is far too low for human survival without specialized equipment. To counteract this, a sophisticated system uses air tapped directly from the running jet engines. This compressed air is cooled, conditioned, and then pumped into the fuselage to create an artificial atmosphere.
The pressure inside the cabin is regulated by a precision outflow valve that constantly releases air to the outside, balancing the rate of incoming air. This controlled environment does not simulate sea-level pressure, because the structural integrity of the fuselage cannot withstand such a large pressure differential at high cruising altitudes. Instead, the cabin atmosphere is typically maintained at a pressure equivalent to an altitude of 6,000 to 8,000 feet above sea level. Newer aircraft designs, such as the Boeing 787 Dreamliner, are built with stronger composite materials that allow the internal pressure to be set even lower, closer to a 6,000-foot equivalent.
Defining Acute Mountain Sickness and Hypoxia
Acute Mountain Sickness (AMS) is a physiological reaction that occurs when the body struggles to adjust to the lower oxygen levels and reduced air pressure found at high elevations. This condition, known as hypobaric hypoxia, results in a lack of sufficient oxygen reaching the body’s tissues. The rapid ascent to high altitudes does not allow the necessary time for the body to acclimatize by increasing breathing rate and red blood cell production.
The mild symptoms of AMS generally include headache, nausea, fatigue, dizziness, and difficulty sleeping. AMS is most frequently triggered when ascending rapidly to elevations at or above 8,000 feet. Severe forms of altitude sickness, like High Altitude Pulmonary Edema (HAPE) or High Altitude Cerebral Edema (HACE), only occur at much higher elevations, typically above 10,000 feet, and are not a concern during commercial flight.
Why Classic Altitude Sickness Is Rare on Planes
True AMS is infrequent during air travel because the pressurized environment keeps the cabin altitude below the conventional threshold for severe sickness. By maintaining a pressure equivalent to 8,000 feet or less, the aircraft ensures the partial pressure of oxygen remains high enough for most healthy individuals. While a minor drop in blood oxygen saturation does occur, it generally falls to about 90%, which is well within the acceptable range for a healthy person.
This mild oxygen reduction is typically not enough to trigger the full syndrome of AMS, especially since passengers are at rest and not exerting themselves. However, the reduced oxygen environment can pose a risk to those with pre-existing cardiopulmonary conditions. Individuals with severe anemia, chronic obstructive pulmonary disease (COPD), or unstable heart failure may experience exacerbated symptoms even at cabin altitudes, as they have a reduced capacity for oxygen uptake or transport.
Common Causes of In-Flight Discomfort
Many common symptoms experienced during a flight that are often mistaken for altitude sickness are actually caused by other factors prevalent in the cabin environment. One of the most frequent complaints is barotrauma, which is pain or pressure in the ears and sinuses. This occurs because the air trapped inside body cavities expands during ascent and contracts during descent, and is unable to equalize quickly through the eustachian tubes or sinus passages.
Dehydration is another significant contributor to in-flight discomfort, manifesting as headaches and general fatigue. The humidity level in a commercial cabin is often extremely low, which accelerates the loss of moisture from the body through respiration. This dry air and the resulting fluid loss can lead to symptoms that mirror the mild aches and fogginess of true altitude sickness. Other non-hypoxic discomforts include fatigue from disrupted sleep and motion sickness.