It’s not uncommon to wake up and almost immediately do a big, window-rattling fart. A properly loud, blanket-lifting, room-filling fart, the kind that the neighbors can hear — one of those that changes the temperature of the room. The sort of fart you could knock ornaments off shelves with. A fart that, if you were locked in a medieval dungeon, you could weaponize by channeling it through the keyhole, sending the chunky medieval key on the outside of the door flying through the dungeon-keeper’s skull. The sort of fart where, if you have a glass of water on your bedside table, you sort of don’t want to drink it afterwards in case it’s been infused with poo. A fart you could kill a shark with.
If you’re a tightly-wound type of person, you can grow to really hate those farts, feeling like they’re proof that even when asleep, you’re not truly relaxed. Farting involves relaxing muscles, so if you didn’t let your honk out when sleeping, what even are you? Every morning’s release can feel like an alarm confirming that you’re failing at sleep, you tired stinking idiot.
Good news, though: Waking up and ripping a fat one doesn’t mean you’re broken.
If you eat regularly, digestive processes are taking place in your body all the time. Farts mostly consist of “fermentation gases” — hydrogen, methane and carbon dioxide formed in the large intestine during the bacterial processes of digestion. The quantities they form in depend on what you’ve been eating, with some foods like onions, garlic, cabbage, fruit, cruciferous vegetables and beans leading to larger amounts being produced, all of which have to come out. These fermentation gases are all odorless, but, again, certain foods lead your body to work in different ways — foods containing sulfur lead to the creation of hydrogen sulfide, which smells like, well, farts.
(Another contributor to farts is swallowing air — eating very fast, smoking, drinking a lot of soda and chewing gum can all take you on board the Butthole Express to Parp City.)
With a morning fart, you have eight(ish) hours of gas built up, which can “pool” as you lie flat, and suddenly shifting to vertical from horizontal when you wake up can move it on a bit to a place it needs to be farted out from. While being vertical isn’t essential for digestion due to peristalsis (the gut’s way of pushing things along), moving around can certainly encourage a fart to come out. That’s why yoga classes are wall-to-wall farts, and watching a child do a forward roll is a multi-sensory experience.
Can’t we just fart it all out while sleeping, though?
Not according to a 1991 study published in the journal Gut, which used rectal catheters to measure farting in volunteers fed half a can of beans on top of their normal diet. (“Hello, I am a scientist. Here is half a can of beans. Show me your asshole please, so I can smell it all night with this pipe.”)
The study found that while night-farts did happen, they happened significantly less frequently than waking ones. There are bodily functions, such as sneezing, that are suspended during sleep due to certain neurotransmitters being shut down. This, combined with the muscle paralysis involved in sleep (which is what, among other things, stops most people from peeing the bed), suggests that the farts that do come out while dreaming might be entirely involuntary.
Most farts you do while awake are at least slightly opt-in — you usually have enough control over the exact second of release to, depending on your personality, walk away or demand someone pull your finger. It seems highly possible that midnight cheese-cutting occurs when enough gas builds up that it’s just a matter of physics, and no muscle movement is actually involved, with a bubble of flatus simply forcing its way out of the body.
Tragically, science is yet to investigate this thoroughly.