We all know the feeling. The telltale build-up of hydrogen and methane in your large intestine. The discomfort as the gases expand and the mortal dread that comes as the pressure builds. They want out. They're going to evacuate, violently if necessary, from one end of the digestive tract or the other, as is nature's way. But why now? Why here, in the middle of a job interview or the first meeting with your partner's aristocratic parents?
Flatulence doesn't care about your schedule, unfortunately. But it could be a lot worse than a burp over dinner or a bottom burp in an overpopulated elevator. Spare a thought for the characters of A Quiet Place, the sci-fi-horror film starring Emily Blunt in which blind, carnivorous aliens hunt people down with their acute sense of hearing. Forget the embarrassment, this is a world in which farts are fatal.
As A Quiet Place Part II is released in cinemas, it got us thinking. How long could a human being suppress a touch of the windy-pops? And what would happen if you tried to hold it for too long? Strangely, the scientific literature is somewhat thin, but some researchers do have insights because what happens when we fart is fairly well understood.
"On average, a person passes wind around 15 times a day," says Julie Thomson at the digestive health charity Guts UK. "We really don’t know how long a person could go without passing wind (and the safety aspects of that) from a science basis – it also has to be said that it would be difficult to suppress wind for long."
We expel around 2.5 litres of gas a day. It could be air we've inadvertently swallowed or gas released when gut bacteria get to work on undigested carbohydrates. When we try to hold in a toot, a guff, an angel's whisper, we feel discomfort – but it can potentially lead to other problems, too.
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Professor Claire Collins is research director at the University of Newcastle School of Health in Australia. In an article for The Conversation, she discussed research which linked the retention of gas to a condition called diverticulitis, where 'pouches' develop in your gut lining and lead to inflammation. The jury's out, she tells Science Focus.
"It's unclear whether the risk of diverticulitis was increased or not," she says. "The main research [is] related to reabsorption of gasses and then expulsion in the breath."
That's right. A fart you hold in for too long could eventually be expelled as foul breath, as your stomach balloons until some of the gas is reabsorbed into your circulation. When you bear in mind that this can include hydrogen sulphide – the stuff that causes the smelliest farts – maybe holding in wind isn't worth the effort.
But what about poor old Emily Blunt in A Quiet Place? Even then, where an unexpected trumpet could bring a pack of monsters down on you, letting rip is better than holding tight. Because, says Thomson, the more you hold it in, the more likely it is to make a noise since that only builds pressure inside your body.
"The sound is made by the speed (or perhaps more precisely the pressure) of the gas and this might depend on the contractions of the bowel and the amount of gas produced and the shape of the anus – narrower will likely produce more sound," she says.
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"There are ways of reducing it but the options in a healthy person would be to reduce ingested gas. Reduce carbonated drinks, stop chewing gum, stop smoking and eat slowly, chewing food well. If fibre is reduced, this results in constipation which is not helpful and could make the situation worse."
Got that, Em?
A former deputy editor at Science Focus, Ian once undertook a scientific ranking of the UK's best rollercoasters on behalf of the magazine. He is now a freelance writer, which is frankly a lot less fun.