Flatulence is defined in the medical literature as "flatus expelled through the anus" or the "quality or state of being flatulent",[1] which is defined in turn

Flatulence is defined in the medical literature as "flatus expelled through the anus" or the "quality or state of being flatulent",[1] which is defined in turn as "marked by or affected with gases generated in the intestine or stomach; likely to cause digestive flatulence".[2] The root of these words is from the Latin flatus – "a blowing, a breaking wind".[3] Flatus is also the medical word for gas generated in the stomach or bowels.[4] Despite these standard definitions, a proportion of intestinal gas may be swallowed environmental air, and hence flatus is not totally generated in the stomach or bowels. The scientific study of this area of medicine is termed flatology.[5] Flatus is brought to the rectum and pressurized by muscles in the intestines. It is normal to pass flatus, though volume and frequency vary greatly among individuals. It is also normal for intestinal gas to have a feculent odor, which may be intense. The noise commonly associated with flatulence ("blowing a raspberry") is produced by the anus and buttocks, which act together in a manner similar to that of an embouchure. Both the sound and the smell are sources of embarrassment, annoyance or flatulence humor. There are several general symptoms related to intestinal gas: pain, bloating and abdominal distension, excessive flatus volume, excessive flatus smell, and gas incontinence. Furthermore, eructation ("an act or instance of belching", colloquially known as "burping") is sometimes included under the topic of flatulence.[6] When excessive or malodorous, flatus can be a sign of a health disorder, such as irritable bowel syndrome, celiac disease or lactose intolerance.[7] Contents 1    Terminology 2    Signs and symptoms 2.1    Bloating and pain 2.2    Excessive volume 2.3    Smell 2.4    Incontinence of flatus 3    Cause 4    Mechanism 4.1    Production, composition, and smell 4.2    Volume and intestinal gas dynamics 5    Management 5.1    Pain and bloating 5.2    Volume 5.3    Smell 5.4    Incontinence 6    Society and culture 6.1    Environmental impact 6.2    Entertainment 6.3    Religion 7    See also 8    References 9    External links Terminology MENU0:00 A human flatulence Non-medical definitions of the term include "the uncomfortable condition of having gas in the stomach and bowels", or "a state of excessive gas in the alimentary canal". These definitions highlight that many people consider "bloating", abdominal distension or increased volume of intestinal gas, to be synonymous with the term flatulence (although this is technically inaccurate). Colloquially, flatulence may be referred to as "farting", "pumping", "trumping",[8] "blowing off", "pooting", "passing gas", "breaking wind" or simply (in American English) "gas" or (British English) "wind". Derived terms include vaginal flatulence, otherwise known as a queef. Signs and symptoms Generally speaking, there are four different types of complaints that relate to intestinal gas, which may present individually or in combination. Bloating and pain Patients may complain of bloating as abdominal distension, discomfort and pain from "trapped wind". In the past, functional bowel disorders such as irritable bowel syndrome that produced symptoms of bloating were attributed to increased production of intestinal gas. However, three significant pieces of evidence refute this theory. First, in normal subjects, even very high rates of gas infusion into the small intestine (30 mL/min) is tolerated without complaints of pain or bloating and harmlessly passed as flatus per rectum.[9] Secondly, studies aiming to quantify the total volume of gas produced by patients with irritable bowel syndrome (some including gas emitted from the mouth by eructation) have consistently failed to demonstrate increased volumes compared to healthy subjects. The proportion of hydrogen produced may be increased in some patients with irritable bowel syndrome, but this does not affect the total volume.[10] Thirdly, the volume of flatus produced by patients with irritable bowel syndrome who have pain and abdominal distension would be tolerated in normal subjects without any complaints of pain. Patients who complain of bloating frequently can be shown to have objective increases in abdominal girth, often increased throughout the day and then resolving during sleep. The increase in girth combined with the fact that the total volume of flatus is not increased led to studies aiming to image the distribution of intestinal gas in patients with bloating. They found that gas was not distributed normally in these patients: there was segmental gas pooling and focal distension.[9] In conclusion, abdominal distension, pain and bloating symptoms are the result of abnormal intestinal gas dynamics rather than increased flatus production. Excessive volume As mentioned above, the normal range of volumes of flatus in normal individuals varies hugely (476–1,491 mL/24 h).[5] All intestinal gas is either swallowed environmental air, present intrinsically in foods and beverages, or the result of gut fermentation. Swallowing small amounts of air occurs while eating and drinking. This is emitted from the mouth by eructation (burping) and is normal. Excessive swallowing of environmental air is called aerophagia, and has been shown in a few case reports to be responsible for increased flatus volume. This is, however, considered a rare cause of increased flatus volume. Gases contained in food and beverages are likewise emitted largely through eructation, e.g., carbonated beverages. Endogenously produced intestinal gases make up 74 percent of flatus in normal subjects. The volume of gas produced is partially dependent upon the composition of the intestinal microbiota, which is normally very resistant to change, but is also very different in different individuals. Some patients are predisposed to increased endogenous gas production by virtue of their gut microbiota composition.[9] The greatest concentration of gut bacteria is in the colon, while the small intestine is normally nearly sterile. Fermentation occurs when unabsorbed food residues may arrive in the colon. Therefore, even more than the composition of the microbiota, diet is the primary factor that dictates the volume of flatus produced.[9] Diets that aim to reduce the amount of undigested fermentable food residues arriving in the colon have been shown to significantly reduce the volume of flatus produced. Again, increased volume of intestinal gas will not cause bloating and pain in normal subjects. Abnormal intestinal gas dynamics will create pain, distension, and bloating, regardless of whether there is high or low total flatus volume. Smell Although flatus possesses physiological smell, this may be abnormally increased in some patients and cause social distress to the patient. Increased smell of flatus presents a distinct clinical issue from other complaints related to intestinal gas.[11] Some patients may exhibit over-sensitivity to bad flatus smell, and in extreme forms, olfactory reference syndrome may be diagnosed. Recent informal research found a correlation between flatus smell and both loudness and humidity content [12] Incontinence of flatus "Gas incontinence" could be defined as loss of voluntary control over the passage of flatus. It is a recognised subtype of faecal incontinence, and is usually related to minor disruptions of the continence mechanisms. Some consider gas incontinence to be the first, sometimes only, symptom of faecal incontinence.[13] Cause Intestinal gas is composed of varying quantities of exogenous sources and endogenous sources.[14] The exogenous gases are swallowed (aerophagia) when eating or drinking or increased swallowing during times of excessive salivation (as might occur when nauseated or as the result of gastroesophageal reflux disease). The endogenous gases are produced either as a by-product of digesting certain types of food, or of incomplete digestion, as is the case during steatorrhea. Anything that causes food to be incompletely digested by the stomach or small intestine may cause flatulence when the material arrives in the large intestine, due to fermentation by yeast or prokaryotes normally or abnormally present in the gastrointestinal tract. Flatulence-producing foods are typically high in certain polysaccharides, especially oligosaccharides such as inulin. Those foods include beans, lentils, dairy products, onions, garlic, spring onions, leeks, turnips, swedes, radishes, sweet potatoes, potatoes, cashews, Jerusalem artichokes, oats, wheat, and yeast in breads. Cauliflower, broccoli, cabbage, Brussels sprouts and other cruciferous vegetables that belong to the genus Brassica are commonly reputed to not only increase flatulence, but to increase the pungency of the flatus.[15][16] In beans, endogenous gases seem to arise from complex oligosaccharides (carbohydrates) that are particularly resistant to digestion by mammals, but are readily digestible by gut flora – microorganisms (methane-producing archaea; Methanobrevibacter smithii) that inhabit the digestive tract. These oligosaccharides pass through the upper intestine largely unchanged, and when they reach the lower intestine, bacteria feed on them, producing copious amounts of flatus.[17] When excessive or malodorous, flatus can be a sign of a health disorder, such as irritable bowel syndrome, celiac disease, non-celiac gluten sensitivity or lactose intolerance. It can also be caused by certain medicines, such as ibuprofen, laxatives, antifungal medicines or statins.[7][18] Some infections, such as giardiasis, are also associated with flatulence.[19] Interest in the causes of flatulence was spurred by high-altitude flight and human spaceflight; the low atmospheric pressure, confined conditions, and stresses peculiar to those endeavours were cause for concern.[17] In the field of mountaineering, the phenomenon of high altitude flatus expulsion was first recorded over two hundred years ago. Mechanism Production, composition, and smell Flatus (intestinal gas) is mostly produced as a byproduct of bacterial fermentation in the gastrointestinal (GI) tract, especially the colon.[20] There are reports of aerophagia (excessive air swallowing) causing excessive intestinal gas, but this is considered rare.[21] Over 99% of the volume of flatus is composed of odorless gases.[5] 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.[22] Hydrogen, carbon dioxide and methane are all produced in the gut and contribute 74% of the volume of flatus in normal subjects.[23] Methane and hydrogen are flammable, and so flatus can be ignited if it contains adequate amounts of these components.[24] Not all humans produce flatus that contains methane. For example, in one study of the faeces of nine adults, only five of the samples contained archaea capable of producing methane.[25] The prevalence of methane over hydrogen in human farts 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.[26] The remaining trace (<1% volume) compounds give flatus its smell. Historically, compounds such as indole, skatole, ammonia and short chain fatty acids were thought to cause the smell of flatus. More recent evidence proves that the major contribution to the smell of flatus comes from a combination of volatile sulfur compounds.[5][27] 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 a mothball smell, and therefore probably do not contribute greatly to the