In-flight flatulence is a common discomfort – so what causes it? And what can we do to save embarrassment? David Robson speaks to a Danish doctor with some surprising answers.

Jacob Rosenberg’s interest with in-flight flatulence began on a long-haul trip to a New Zealand. He looked down at his stomach and it seemed to have visibly grown since he stepped on the plane. When he opened his bag and saw his empty bottle of water this made sense. The bottle had expanded in the low pressure and then crumpled as the plane reached the ground. The gases in his stomach, he realised, must have been doing exactly the same thing.

"Since then, I’ve noticed just how much flatulence you have on a flight,” he says. “Which is very much.”

While hardly comparable to the effects of outside turbulence, wind inside planes is a common complaint. “When you talk to people, they have all experienced a bad odour at some time,” says Rosenberg, who is a clinical professor at the University of Copenhagen. But it was only once he was back on the ground and having a few drinks with his colleagues that he began to think seriously about the scientific consequences of this. The result was a paper that might just suggest ways to relieve our discomfort on flights.

Even on the ground, we all pass a surprising quantity of gas every day. According to one estimate, the average person breaks wind 10 times every 24 hours, expelling about 1 litre in total. The gases are brewed from food that has failed to be absorbed by the gut, and so is fermented by bacteria, which produce nitrogen, carbon dioxide, and hydrogen – along with more odorous, sulphurous compounds.

It may be a universal experience, but as Rosenberg combed the medical literature, he found that there are some surprisingly prevalent misconceptions surrounding our wind. Despite popular belief, studies show men are not more flatulent than women, for example (though they may be more public about it); in fact the same study from the late 90s found women’s flatulence has a higher concentration of the smelly sulphurous compounds, and was rated as having a more potent odour by a few unlucky judges. And although beans may be known “as the musical fruit”, a recent experiment found that it is not nearly as inflammatory as most would believe, and its effects differ widely from person to person. Foods known to reduce flatulence include fish, rice, dairy products, fish and strained fruit juice – since they leave less waste in the gut for fermentation.

Bloated pilots

But if our flatulence on ground level passes mostly unnoticed (or is at least politely ignored) in day-to-day life, it can become something of an unwanted companion in the confines of an air cabin. Its frequency on planes is simple physics, Rosenberg says. “The pressure drops and the air must expand into more space.” That 1 litre of gas now needs to fill a 30% bigger volume, leading to that nasty bloating feeling.  This seems to be a regular problem for pilots – more than 60% report feeling regular abdominal bloating, much higher than the average for office workers.

You could just try to hold it in, of course, but that’s not necessarily a wise idea; besides the discomfort, Rosenberg thinks there could be a slight risk. “If you are young and healthy it’s not a problem, but for a frail old person, it may put strain on cardiac function,” he says.

Freeing the wind has its own potential problems at altitude: one paper from 1969 highlighted the risk of a fireball arising from astronauts’ wind, held in high concentration in the space cabin. Thankfully, no such accidents have been recorded so far. Even so, a team from the Canadian Space Agency recently suggested that fermented soy may be the perfect space food, since it is packed with probiotic bacteria that could compete with the wind-producing microbes – reducing the astronauts’ bloating.

While the worst-case scenario on aeroplanes may be discomfort or embarrassment, airlines have already taken some action. As part of his research for his paper, Rosenberg interviewed aeroplane engineers at Copenhagen, and he found that many airlines already use charcoal filters in the air conditioning. Charcoal is highly porous and has been shown to readily absorb a range of odours – so the filters stop the sulphurous fumes from recirculating around the cabin. Airlines also tend to make sure the in-flight food is low in fibre, but high in carbohydrates – a balance that is more likely to calm our digestion. It’s not clear when or how they came to these decisions – but we can guess that Brussels sprouts and cabbage left the in-flight menu at a fairly early point in aviation history.

Charcoal underpants

Even so, Rosenberg’s personal feeling is that more could be done – particularly since no smoking policies have made other odours more easily discernible. It may be possible to place charcoal within the seats themselves, he suggests – though previous studies have suggested that is not particularly effective, perhaps because most trousers and skirts create a “tunnel effect” that direct the fumes away from the cushion. Instead, he thinks that airlines would do better to use blankets with charcoal woven into the fabric. For people who are especially worried about their own flatulence, he points out that you can now buy underwear designed along similar principles; the American Journal of Gastroenterology reports that charcoal-lined underwear absorbs nearly 100% of the odour, compared to removable (and reusable) pads placed within trousers, which only absorb about 70%.

Rosenberg has some other, more tongue-in-cheek suggestions. The flatulent are more likely to release tell-tale gases resulting from food fermentation through their oesophagus and out of their mouth, which means that certain devices can provide a breath test for people harbouring something in their colon. Airlines could, feasibly, screen passengers at check-in and place you in a special section of the plane, near the toilets – or simply ban entry.

As unpleasant as inflight flatulence is, it would be an extreme solution to, let’s face it, a trivial issue. So perhaps the best answer is just to lose our embarrassment. As Rosenberg says, “Farting is not a rare problem, but we just don’t talk about it”. Let’s hope his paper has gone a little way to remedying that.

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