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Anne Marie Helmenstine, Ph.D.

What Is the Chemical Composition of Farts?

By January 5, 2013

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Fart chemistry depends on the individual. (Getty Images)Have you ever wondered about the chemical composition of farts, or to be more technical, flatus? The exact chemical composition of human flatulence varies from one person to another, based on his or her biochemistry, the bacteria inhabiting the colon and the foods that were eaten. If the gas results from ingesting air, the chemical composition will approximate that of air. If the fart arises from digestion or bacterial production, the chemistry may be more exotic. Farts consist primarily of nitrogen, the principal gas in air, along with a significant amount of carbon dioxide. A typical breakdown of the chemical composition of farts is:

Nitrogen: 20-90%
Hydrogen: 0-50% (flammable)
Carbon dioxide: 10-30%
Oxygen: 0-10%
Methane: 0-10% (flammable)

Lighting Farts on Fire - The Blue Flame

Human flatus may contain hydrogen gas and/or methane, which are flammable. If sufficient amounts of these gases are present, it's possible to light the fart on fire. Keep in mind, not all farts are flammable. Although flatus has great YouTube fame for producing a blue flame, it turns out only about half of people have the archaea (bacteria) in their bodies that are necessary to produce methane. If you don't make methane, you may still be able to ignite your farts (a dangerous practice!), but the flame will be yellow or possibly orange rather than blue.

The Smell of Farts

Flatus often stinks! There are several chemicals that contribute to the smell of farts:
  • skatole (by-product of meat digestion)
  • indole (by-product of meat digestion)
  • methanethiol (a sulfur compound)
  • dimethyl sulfide (a sulfur compound)
  • hydrogen sulfide (rotten egg odor, flammable)
  • volatile amines
  • short chain fatty acids
  • feces (if present in the rectum)
  • bacteria
The chemical composition and thus odor of farts differs according to your health and diet, so you would expect a vegetarian's farts to smell different from those produced by a person who eats meat.

Got questions or comments? Feel free to post a response.


May 18, 2012 at 6:41 am
(1) KevinW says:

I read that flatus produces hydrogen. Over time would flatus (not just human) effectively be splitting oxygen from hydrogen (although not necessarily directly from water)? I have also read that hydrogen can escape the earth’s atmosphere. Could flatus cause an increase in atmospheric oxygen and a decrease in the earth’s mass? Would similar processes in early bacteria (4 bn yrs ago) have enriched the atmosphere to the point where animals could exist (breathe)?

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