A fart is mainly composed of odorless gases such as nitrogen, oxygen, carbon dioxide, hydrogen, and sometimes methane. Nitrogen makes up a large part and comes from swallowed air. Gut bacteria break down food and release hydrogen and carbon dioxide. Less than 1% of a fart contains sulfur compounds, which are responsible for the smell. These include hydrogen sulfide, methanethiol, and dimethyl sulfide, all of which create the characteristic odor. Wondering what else affects this mix of gases?
Everyone farts, and while it might be a source of humor or embarrassment, understanding the gases in a fart can be enlightening. Flatus, the medical term for intestinal gas, is made up of more than 99% odorless gases. The main components are nitrogen, oxygen, carbon dioxide, hydrogen, and sometimes methane. Each of these gases contributes to the total gas produced in your digestive system.
Nitrogen is typically the largest component, making up 20% to 90% of flatus, and mostly comes from swallowed air. Hydrogen can account for up to 50% and is created by gut bacteria as they break down undigested carbohydrates. This fermentation process, along with bacterial production of carbon dioxide and methane, makes up much of the gas released. Carbon dioxide, present in 10% to 30% of flatus, is produced both from swallowed air and from bacterial reactions, including the neutralization of stomach acid. Methane, produced by certain archaea in the gut, isn’t found in everyone but can make up to 10% of flatus. Oxygen is also present in small amounts, mainly from swallowed air.
Although most gases are odorless, the small amount of smelly gases—less than 1%—causes the distinctive odor. Sulfur-containing compounds like hydrogen sulfide, methanethiol, and dimethyl sulfide are mainly responsible for the smell. Hydrogen sulfide gives a rotten egg odor, even in tiny amounts. Methanethiol can smell like rotting vegetables or garlic, while dimethyl sulfide adds a cabbage-like or slightly sweet scent.
These gases originate from two main sources: air that you swallow and gas produced by bacteria in your gut. Eating quickly, drinking carbonated drinks, or chewing gum increases air swallowing, which adds more nitrogen and oxygen. Most swallowed air, however, is released through belching rather than as flatus. Flatulence arises from fermentation by yeast or prokaryotes in the gastrointestinal tract, leading to the production of various gases.
The majority of gas is produced in the large intestine, where bacteria break down undigested carbohydrates, generating hydrogen, carbon dioxide, methane, and sulfur gases. About 74% of the volume of flatus comes from this bacterial activity.
Your diet has a big influence on both the amount and smell of gas. Foods high in fiber, such as beans and whole grains, increase gas production, while sulfur-rich foods like onions and garlic make the odor stronger. Your gut microbiome, food intolerances, medications, and health conditions can also affect the makeup and smell of your gas, so everyone’s flatulence is a bit different. Knowing what causes these differences can help explain this everyday bodily function.
Conclusion
To sum up, passing gas mostly releases nitrogen, oxygen, carbon dioxide, hydrogen, and methane. These result from digestion and the work of gut bacteria. Some gases, like hydrogen sulfide, create odor, while others remain scentless. So, if you feel awkward, remember it’s a normal part of how your body stays balanced. Appreciate the science and humor, and let things happen naturally!
