You board feeling completely normal. Two hours later you’re doing the classic seat-24C shuffle, quietly convinced you’ve never produced this much gas in your life. You didn’t eat anything strange. Nobody spiked the pretzels. What’s actually happening is physics, and it’s a real enough problem that doctors have published peer-reviewed papers with an actual acronym for it.
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The condition is called HAFE, it has a genuine 1981 medical paper behind it, and decades of follow-up research have found the original explanation was only half right. Here’s what’s really going on inside your body at 35,000 feet and 14,000 feet, and why the full answer turned out to be stranger than ‘gas expands when pressure drops.’
Quick answer
Airplane cabins are pressurized to feel like roughly 8,000 feet of altitude, not sea level, and that lower pressure lets trapped intestinal gas expand — by as much as 30% according to aerospace medicine estimates — so it has to escape. The same pressure drop happens on mountains and even short drives to elevation, a phenomenon doctors formally named High-Altitude Flatus Expulsion, or HAFE, in 1981.
The doctors who named it
In February 1981, physicians Paul S. Auerbach and York E. Miller published a short paper in the Western Journal of Medicine titled, with admirable directness, ‘High Altitude Flatus Expulsion (HAFE).’ They described a gastrointestinal syndrome triggered by ascent: as atmospheric pressure falls, gas already sitting in the colon expands, and the frequency and volume of flatulence goes up until you descend again, at which point it resolves on its own.
They weren’t the first to notice. A Russian physician and naturalist named Joseph Hamel documented the effect on Mont Blanc as early as 1820, describing ‘pneumatic flatulence’ alongside shortness of breath and fatigue during the ascent — though the observation was largely forgotten for over 150 years. In 1972, a physician named E.Y. Davis documented the same thing among Everest-region trekkers in a paper called ‘Flatulence Accompanying Rigorous Trekking,’ published in the Kathmandu Medical Bulletin. There was even harder data behind it: a 1969 study by Greenwald, Allen, and Bancroft in the Journal of Applied Physiology had already measured abdominal gas volume changing at altitude versus at ground level. Auerbach and Miller just revived the syndrome and gave it its lasting name — and its acronym.
Then someone took it to the airport
The mountaineering finding eventually migrated indoors, onto airplanes, courtesy of a 2013 paper in the New Zealand Medical Journal called ‘Flatulence on Airplanes: Just Let It Go,’ by Hans Pommergaard, Jakob Burcharth, Anders Fischer, and Jacob Rosenberg of Copenhagen’s Herlev Hospital, along with William Thomas of Sheffield Teaching Hospitals in England.
Their argument was pure applied physics: a cabin held at around 565 mmHg of pressure — the equivalent of 8,000 feet — versus roughly 760 mmHg on the ground means gas in your gut genuinely expands in volume during flight. The average person already produces 0.7 to 1 liter of intestinal gas a day and passes it about 10 times, and the authors’ actual medical recommendation was to let it happen rather than hold it in, since suppression just causes discomfort and bloating. Their proposed fix, only partly tongue-in-cheek: charcoal-lined seat cushions, blankets, and even underwear to absorb the odor, since ordinary cushions already blunt roughly half of it.
The part most people miss
The tidy ‘gas just expands’ story turned out to be incomplete. A 2013 pilot study in Medical Hypotheses, led by Graham Slaney, drove eight volunteers up into the Australian Alps to an altitude of about 5,900 feet — roughly Denver’s elevation, far below where Hamel or later mountaineers had climbed — and still found flatus frequency more than doubled after ascent, with participants recording around 14 expulsions each over an 18-hour window. Stranger still, the surge wasn’t instant: it built over several hours, suggesting the gas wasn’t just old air stretching out under lower pressure. The researchers proposed that carbon dioxide was actively diffusing out of the bloodstream and into the gut in response to the pressure change, effectively manufacturing new gas rather than only expanding what was already there. So the real story isn’t a single simple gas law — it’s your blood chemistry and your plumbing responding to elevation together, which is also why the effect shows up at modest ski-town altitudes, not just on 14,000-foot peaks.
Sources
Paul S. Auerbach and York E. Miller, ‘High Altitude Flatus Expulsion (HAFE),’ Western Journal of Medicine, February 1981.
Hans C. Pommergaard, Jakob Burcharth, Anders Fischer, William E.G. Thomas, and Jacob Rosenberg, ‘Flatulence on Airplanes: Just Let It Go,’ The New Zealand Medical Journal, 2013.
Graham Slaney et al., ‘High Altitude Syndromes at Intermediate Altitudes: A Pilot Study in the Australian Alps,’ Medical Hypotheses, 2013, plus the historical record of Joseph Hamel’s 1820 Mont Blanc expedition, as summarized on PubMed and Wikipedia’s entry on High-altitude flatus expulsion.
Explore more: More true stories about your amazing body.
HAFE (High-Altitude Flatus Expulsion) FAQs
Why do I fart more on airplanes specifically?
Airplane cabins are pressurized to roughly the equivalent of 8,000 feet of altitude, well below sea-level pressure, which lets intestinal gas expand and increases how much and how often you need to pass it.
Is HAFE dangerous?
No — High-Altitude Flatus Expulsion is uncomfortable, not harmful, and resolves on its own once you return to lower altitude or land. Doctors who’ve studied it actually recommend letting it out rather than holding it in.
At what altitude does this start happening?
Research has found increased flatulence at altitudes as modest as about 5,900 feet, a 2013 Australian Alps study found, though the phenomenon was first documented during an 1820 Mont Blanc ascent well above 11,000 feet.
Is it just trapped gas expanding, or something else?
Both. Lower pressure does expand existing gas, but a 2013 study suggests the body may also generate additional gas by letting carbon dioxide diffuse from the bloodstream into the intestines during ascent.
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