This is Why You Fart So Much at Altitude

It’s called high-altitude flatus expulsion, and yes, it’s a real thing.

Photo: Sergey Pesterev

Heading out the door? Read this article on the new Outside+ app available now on iOS devices for members! Download the app.

I huffed and puffed as I approached the summit of Mt. Kilimanjaro. In retrospect, some of my puffs weren’t just breath.

At 19,341 feet Kilimanjaro is the highest peak in Africa, and draws about 35,000 climbers every year. But those visitors are leaving more than footprints: Rip-roaring bouts of flatulence are standard-issue up here. An article in the Huffington Post estimated that these climbers release 75 cubic meters of intestinal gas in a year. (I don’t know how they arrived at that figure. I’m just glad I was not the one who measured all those fumes.)

When I asked my Tanzanian guides, Arnold Fredrick and Michael John, if climbers fart much on Kilimanjaro, they looked at me, confused. Then I made a noise like an eighth grader, and they laughed. Yes, they said, climbers do tend to blaze a trail, especially on summit day.

It turns out that smelly condition has a name: high altitude flatus expulsion, or HAFE. Its discoverers—the pioneers of alpine flatulence—are Dr. Paul Auerbach, Redlich Family Professor Emeritus at the Stanford University School of Medicine and a founder of the Wilderness Medical Society, and Dr. York Miller, professor of pulmonary and critical care medicine at the University of Colorado School of Medicine.

In the summer of 1980, the two young doctors were hiking in the San Juan Mountains of southwestern Colorado, on a mission to summit three 14ers. When they climbed above 11,000 feet, they noticed something didn’t smell right.

On the trail and in the tent, their bodies emitted noxious fumes. The two friends accused each other of being the guiltier culprit. The farts flew so frequently, Dr. Miller said, that “informally we were trying to outdo each other.”

“I thought it was all the freeze-dried chili he was eating, and nuts and GORP and beans,” Dr. Auerbach said. All the beer they downed might have contributed, too.

About how much gas did he and Dr. Miller pass?

“I can’t give you the exact volume,” Dr. Auerbach replied without hesitation, “but it was enough to blow up at least five party balloons. The good part was it seemed to keep the insects away.”

Even the best sleeping bag can contain only so much stench before it leaks out. At night, Dr. Auerbach curled up against the tent wall, struggling to get as far away from his friend as he could.

Dr. Auerbach wondered if there was a name for this odoriferous condition. Dr. Miller suggested Rocky Mountain barking spiders. They decided that if they were going to publish their findings, they’d need a more formal moniker.

Familiar with high altitude pulmonary edema and high altitude cerebral edema, Dr. Auerbach suggested high altitude flatus expulsion. Like the physical phenomenon it was named after, the moniker had a certain ring to it.

When they returned to their homes, the pair sent a letter about their discovery to the prestigious New England Journal of Medicine, but it held its nose. They then submitted it to the now-defunct Western Journal of Medicine, which published the letter in its February 1981 issue.

In the letter, the doctors attributed the disorder to the “expansion of colonic gas at the decreased atmospheric pressure of high altitude.” or Boyle’s law.

“Take a balloon and blow it up at sea level and carry it to the top of Kilimanjaro,” Dr. Miller said. “The balloon is going to get bigger. There’s less atmospheric pressure on the outside of it.” Likewise, he continued, there’s less atmospheric pressure on the outside of a hiker at high altitude, and any bubbles in his or her gastro-intestinal tract will expand. It’s similar to the bends experienced by some deep-sea divers but not as serious.

The doctors now say they don’t know for sure what causes high-altitude flatulence.

Perhaps the lower concentration of oxygen at altitude affects the bowels’ ability to move digested food, Dr. Auerbach theorized, giving it more time to create gas.

In subsequent months, the Western Journal published a flurry of letters on high-altitude farting from sympathetic readers. Perhaps they were relieved to know that they had not suffered alone. Bombarded editors eventually pulled the plug.

Drs. Auerbach and Miller’s discovery became a kind of legend in the backpacking community. Thirty-six years later, a six-minute short titled HAFE: The Story Behind, released at Telluride Mountainfilm, commemorated their discovery. In the movie, Dr. Miller said he had received more notoriety from his HAFE letter than any of the other 150-plus scientific manuscripts that he has published.

Of course, many guilty hikers are loath to admit their dirty deed.

“When my wife is hiking at high altitude, I know she’s going to start [passing gas] because she starts talking louder,” Dr. Auerbach said. “I don’t know if she wants that in the national press, but the kids know all about it.”

I got my own close-up look at HAFE on summit day. As I trudged to Kilimanjaro’s summit, I made a special point to note how my digestive system was responding to the higher elevation. I recorded my first gastric blast about 1:30 a.m. After that, my brain entered a high-altitude fog that clouded memory and perception. I could scarcely think of anything, except taking another step and trying not to roll down the mountain.

Afterwards, I asked Arnold how my digestive system performed. “Yes, you farted a lot,” he responded. “The good thing is that all this farting doesn’t destroy the mountain.” He added that, while Tanzanians looked down their noses at farting in public, they were willing to give foreigners a pass.

I asked Arnold and Dr. Auerbach: if trekkers feel the need to let loose on the trail, what should they do?

Let it go, they agreed. Holding it may cause too much discomfort.

“I don’t know why people are ashamed of it,” added Dr. Auerbach. “It’s a natural process, and at altitude it’s enhanced.” If anything, “you shouldn’t put your hind end into a campfire, because back flashes are a real phenomenon. I’ve never heard of anybody exploding because of that, but people have been singed where they don’t want to be.”

And that, readers, is the toot, the whole toot, and nothing but the toot.

Trending on Backpacker