Editing Flatulence (section)

===Production, composition, and odor===
Flatus (intestinal gas) is mostly produced as a byproduct of bacterial fermentation in the gastrointestinal (GI) tract, especially the [[Colon (anatomy)|colon]].<ref name="Tomlin 1991" /> There are reports of [[aerophagia]] (excessive air swallowing) causing excessive intestinal gas, but this is considered rare.<ref name="Hemmink 2009">{{cite journal |last=Hemmink |first=GJ |author2=Weusten, BL |author3=Bredenoord, AJ |author4=Timmer, R |author5= Smout, AJ |title=Aerophagia: excessive air swallowing demonstrated by esophageal impedance monitoring |journal=[[Clinical Gastroenterology and Hepatology]] |date=October 2009 |volume=7 |issue=10 |pages=1127–29 |pmid=19602452 |doi=10.1016/j.cgh.2009.06.029|doi-access=free }}</ref>

Over 99% of the volume of flatus is composed of odorless gases.<ref name="Tangerman 2009" /> These include [[oxygen]], [[nitrogen]], [[carbon dioxide]], [[hydrogen]] and [[methane]]. Nitrogen is not produced in the gut, but a component of environmental air. Patients who have excessive intestinal gas that is mostly composed of nitrogen have aerophagia.<ref name="Levitt 1998" /> Hydrogen, carbon dioxide and methane are all produced in the gut and contribute 74% of the volume of flatus in normal subjects.<ref name="Suarez 1997" /> Methane and hydrogen are [[flammable]], and so [[Fart lighting|flatus can be ignited]] if it contains adequate amounts of these components.<ref name="Mercer2009">{{cite book |last=Mercer |first=Bobby |title=How Do You Light a Fart?: And 150 Other Essential Things Every Guy Should Know about Science |url=https://books.google.com/books?id=gV01_pPEO_AC&pg=PT88 |date=2009-04-18 |publisher=[[Adams Media]] |isbn=9781440519871 |page=71 |access-date=October 2, 2014 }}{{Dead link|date=March 2024 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>

Not all humans produce flatus that contains methane. For example, in one study of the [[feces|faeces]] of nine adults, only five of the samples contained [[archaea]] capable of producing methane.<ref>{{cite journal| author=Miller TL|author2=Wolin MJ |author3=de Macario EC |author4=Macario AJ | title=Isolation of ''Methanobrevibacter smithii'' from human faeces| journal=[[Applied and Environmental Microbiology]] | year=1982| volume=43| pages=227–32 |pmid=6798932 |pmc=241804 |doi= 10.1128/AEM.43.1.227-232.1982| issue=1|bibcode=1982ApEnM..43..227M }}</ref> The prevalence of methane over hydrogen in human flatus may correlate with obesity, constipation and irritable bowel syndrome, as archaea that oxidise hydrogen into methane promote the metabolism's ability to absorb fatty acids from food.<ref name="Pimentel2012">{{cite journal |last=Pimentel |first=Mark |author2=Robert P Gunsalus |author3=Satish SC Rao |author4=Husen Zhang |year=2012|title=Methanogens in Human Health and Disease |journal=[[The American Journal of Gastroenterology|The American Journal of Gastroenterology Supplements]] |volume=1 |issue=1 |pages=28–33|doi=10.1038/ajgsup.2012.6 |doi-access=free }}</ref>

The remaining trace (<1% volume) compounds contribute to the odor of flatus. Historically, compounds such as [[indole]], [[skatole]], [[ammonia]] and [[short chain fatty acids]] were thought to cause the odor of flatus. More recent evidence proves that the major contribution to the odor of flatus comes from a combination of volatile [[sulfur]] compounds.<ref name="Tangerman 2009" /><ref name="Suarez 1998">{{cite journal |last=Suarez |first=FL |author2=Springfield, J |author3=Levitt, MD |title=Identification of gases responsible for the odour of human flatus and evaluation of a device purported to reduce this odour |journal=[[Gut (journal)|Gut]] |date=July 1998 |volume=43 |issue=1 |pages=100–04 |pmid=9771412 |pmc=1727181 |doi=10.1136/gut.43.1.100}}</ref> [[Hydrogen sulfide]], [[methyl mercaptan]] (also known as [[methanethiol]]), [[dimethyl sulfide]], [[dimethyl disulfide]] and [[dimethyl trisulfide]] are present in flatus. The benzopyrrole volatiles [[indole]] and [[skatole]] have an odor of mothballs, <!-- <ref name="Moore 1987" /> ref name not defined--> and therefore probably do not contribute greatly to the characteristic odor of flatus.

In one study, hydrogen sulfide concentration was shown to correlate convincingly with perceived bad odor of flatus, followed by methyl mercaptan and dimethyl sulfide.<ref name="Levitt 1998" /> This is supported by the fact that hydrogen sulfide may be the most abundant volatile sulfur compound present. These results were generated from subjects who were eating a diet high in [[pinto beans]] to stimulate flatus production.

Others report that methyl mercaptan was the greatest contributor to the odor of flatus in patients not under any specific dietary alterations.<ref name="Tangerman 2009" /><!-- <ref name="Moore 1987" /> no ref name defined --> It has now been demonstrated that methyl mercaptan, dimethyl sulfide, and hydrogen sulfide (described as decomposing vegetables, unpleasantly sweet/wild radish and rotten eggs respectively) are all present in human flatus in concentrations above their smell perception thresholds.<ref name="Tangerman 2009" />

It is recognized that increased dietary sulfur-containing amino acids significantly increases the odor of flatus. It is therefore likely that the odor of flatus is created by a combination of volatile sulfur compounds, with minimal contribution from non-sulfur volatiles.<ref name="Levitt 1998" /> This odor can also be caused by the presence of large numbers of microflora [[bacteria]] or the presence of faeces in the rectum. Diets high in protein, especially sulfur-containing amino acids, have been demonstrated to significantly increase the odor of flatus.