Flatulence Facts

Last reviewed on 2026-04-24.

Beneath the laughter, farting is a normal and surprisingly interesting biological process. This page collects general knowledge about flatulence — why it happens, how often, what makes some farts smell, and how gas behaves in the body. The information here is for general interest only and is not medical advice. If you are worried about your own symptoms, speak to a qualified healthcare professional.

What Causes Farts?

Flatulence forms when bacteria in the large intestine break down food that the small intestine did not fully digest. The bacteria produce gases — mostly nitrogen, hydrogen, carbon dioxide and sometimes methane — which need to exit the body. Belching releases air from the stomach and oesophagus; farting releases gas generated lower down the digestive tract.

A large share of intestinal gas also comes from swallowed air while eating, drinking or chewing gum. The rest comes from bacterial fermentation of undigested carbohydrates in the colon. Certain sugars, such as raffinose (found in beans) and lactose (in dairy), are particularly difficult for many people to break down, which tends to increase gas production.

How Often Do We Fart?

Adults typically pass gas somewhere around 10 to 20 times per day, producing roughly 0.5 to 2 litres of gas over 24 hours. Up to about 21 toots per day is generally considered within the normal range.

Frequency varies with diet, gut microbiome composition and overall digestive health. Most flatulence occurs during bowel movements or within an hour or two after meals. The anal sphincter relaxes slightly during sleep, which is why some people notice more gas in the morning. Swallowed air during heavy breathing — during exercise, for example — can also increase flatulence briefly.

Why Do Some Farts Smell?

About 99 percent of the gas in an average fart is odourless — mostly nitrogen, oxygen, carbon dioxide, hydrogen and methane. The smell comes from trace sulfur compounds produced when gut bacteria break down sulfur-rich foods such as broccoli, cauliflower, Brussels sprouts, eggs and dairy.

The main smelly culprits are hydrogen sulfide (a rotten-egg smell), methanethiol (like rotten cabbage) and dimethyl sulfide. These compounds are detectable by humans at extremely low concentrations, which is why even a tiny amount can make a noticeable impression. Protein-rich diets tend to produce smellier gas because of the extra sulfur, while carbohydrate-heavy diets tend to produce more volume but less odour.

Can You Hold in a Fart?

Many of us have tried to clench through a potentially embarrassing moment. In general, you cannot hold in a fart forever — the gas will eventually find its way out, sometimes more noticeably for having waited. Regularly suppressing gas can contribute to bloating and abdominal discomfort. When you can, letting gas pass is usually the more comfortable option.

The Science of Fart Sounds

Fart sounds depend on three things: the amount of gas being released, the force behind its exit, and how tightly the anal sphincter is held. A tighter sphincter produces higher-pitched notes; a relaxed one gives a lower rumble. When liquid is present, gas bubbling through it produces the characteristic wet popping sound. Body position and clothing also affect the acoustics.

Fart Vocabulary

The medical term for a fart is flatus, borrowed from Latin. The rumbling sound your stomach and intestines make as gas and liquid move around is called borborygmus. Everyday English has produced a long list of creative alternatives: cutting the cheese, breaking wind, letting one rip, blowing a raspberry, passing gas, and plenty more. Modern slang continues to invent new ones, from "crop dusting" (farting while walking) to "Dutch oven" (farting under blankets).

Historical Fart Facts

Humans have found farts funny for a long time. The earliest recorded joke, generally dated to ancient Sumer around 1900 BCE, is a fart joke. Authors as varied as Chaucer and Shakespeare worked flatulent humour into their writing. In the 18th century, Benjamin Franklin wrote a satirical essay titled "Fart Proudly" proposing that scientific study be turned toward flatulence. Edo-period Japan produced a run of "he-gassen" (fart-battle) scrolls depicting elaborate fart duels. Fart humour keeps coming back because its raw material never really changes.

Farts in Space and Extreme Environments

Spaceflight raises unusual questions about flatulence. In microgravity, gas doesn't rise the way it does on Earth, and methane and hydrogen are flammable in an oxygen-rich cabin. Spaceflight programmes pay attention to astronaut diets partly for this reason. At the other extreme, high altitude tends to produce more gas because the lower outside pressure lets intestinal gas expand — a phenomenon sometimes nicknamed HAFE (high-altitude flatus expulsion) by mountaineers.

Animal Flatulence

Humans aren't the only animals that fart. Cattle are significant producers of methane as part of their digestive process, which is one reason livestock gas has become a topic in climate research. Dogs, horses and many other mammals pass gas regularly. Birds generally don't fart, and neither do most fish, due to very different digestive anatomies. Some species use gas in unexpected ways — the bootlace worm and certain fish have been observed using gas for communication or defence.

When to See a Doctor

Passing gas is normal, but excessive flatulence combined with other symptoms can sometimes indicate a digestive issue. Consider talking to a healthcare professional if you experience persistent abdominal pain, sudden changes in bowel habits, unexplained weight loss, blood in the stool, or severe bloating that doesn't settle. Conditions such as lactose intolerance, coeliac disease, small intestinal bacterial overgrowth (SIBO) or irritable bowel syndrome (IBS) can all affect gas production. A food diary is often a useful first step in working out personal triggers.

This page provides general educational information only and is not a substitute for professional medical advice, diagnosis or treatment.