Human feces (American English) orfaeces (British English), commonly and in medical literature more often calledstool,[1] are the solid or semisolid remains of food that could not be digested or absorbed in thesmall intestine of humans, but has been further broken down by bacteria in thelarge intestine.[2][3] It also contains bacteria and a relatively small amount ofmetabolic waste products such as bacterially alteredbilirubin, and the dead epithelial cells from the lining of the gut.[2] It is discharged through theanus during a process calleddefecation.
Human feces has similarities to the feces of other animals and varies significantly in appearance (i.e. size, color, texture), according to the state of the diet,digestive system, and general health. Normally, human feces are semisolid, with amucus coating. Small pieces of harder, less moist feces can sometimes be seen impacted in thedistal (final or lower) end. This is a normal occurrence when a priorbowel movement is incomplete, and feces are returned from therectum to the largeintestine, where water is further absorbed.
Human feces together with humanurine are collectively calledhuman waste orexcretion. Containing human feces and preventing spread ofpathogens from human feces by thefecal–oral route are the main goals ofsanitation.
The Bristol stool scale is a medical aid designed to classify the form of human feces into seven categories. Sometimes referred to in the UK as the Meyers Scale, it was developed by K.W. Heaton at theUniversity of Bristol and was first published in theScandinavian Journal of Gastroenterology in 1997.[4] The form of the stool depends on the time it spends in thecolon.[5]
The seven types of stool are:
Types 1 and 2 indicateconstipation. Types 3 and 4 are optimal, especially the latter, as these are the easiest topass. Types 5–7 are associated with increasing tendency todiarrhea or urgency.[5]
Meconium is a newborn infant's first feces.
Human fecal matter varies significantly in appearance, depending on diet and health.
Feces possesses physiological odor, which can vary according to diet and health status. For example, meat protein is rich in the amino acidmethionine, which is a precursor of the sulfur-containing odorous compounds listed below.[12][13][14][15][16] The odor of human feces is suggested to be made up from the following odorant volatiles:[13]
(H2S) is the most common volatile sulfur compound in feces.[13] The odor of feces may be increased when various pathologies are present, including:[17]
Attempts to reduce the odor of feces (andflatus) are largely based on animal research carried out with industrial applications, such as reduced environmental impact of pig farming. See also:Flatulence#Management, odor. Many dietary modifications/supplements have been researched, including:
On average, healthy humans eliminate 128 g of fresh feces per person per day with apH value of around 6.6 as indicated by aFecal pH test.[23] Fresh feces contains around 75% water and the remaining solid fraction is 84–93% organic solids along with some insoluble phosphate salts.
These organic solids consist of: 25–54% bacterial biomass, 2–25% protein or nitrogenous matter, 25% carbohydrate or undigested plant matter, and 2–15% fat. Protein and fat come from the colon due to secretion, epithelial shedding, and gut bacterial action. These proportions vary considerably depending on many factors but mainly diet and body weight.[24] The remaining solids are composed of insoluble calcium and iron phosphate salts, intestinal secretions, small amounts of driedepithelial cells, andmucus.[24]
Sometimes undigested food may make an appearance in feces. Common undigested foods found in human feces are seeds, nuts, and corn, mainly because of their highfiber content. Beets may turn feces different hues of red. Artificial food coloring in some processed foods, such as highly colorful packaged breakfast cereals, can cause an unusual coloring of feces if eaten in sufficient quantities.
Undigested objects such as seeds can pass through the human digestive system, and latergerminate. One result of this istomato plants growing where treatedsewage sludge has been used asfertilizer.
Clinical laboratory examination of feces, usually termed as stool examination orstool test, is conducted for the sake of diagnosis; for example, to detect the presence of parasites such aspinworms and their eggs (ova) or to detect disease-spreading bacteria. Astool culture—the controlled growth of microbial organisms inculture media under laboratory conditions—sometimes is performed to identify specific pathogens in stool. Thestool guaiac test (or guaiac fecal occult blood test) is conducted to detect the presence of blood in stool that is not apparent to the unaided eye.
The main pathogens that are commonly looked for in feces include:
Intestinal parasites and theirova (eggs) can sometimes be visible to thenaked eye.
Feces can be analyzed for various markers that are indicative of various diseases and conditions. For example,fecal calprotectin levels indicate an inflammatory process such asCrohn's disease,ulcerative colitis, andneoplasms (cancer).
| Reference ranges for fecal markers | |||||
|---|---|---|---|---|---|
| Marker | Patient type | Upper limit | Unit | ||
| Calprotectin | 2–9 years | 166[25] | μg/g of feces | ||
| 10–59 years | 51[25] | ||||
| ≥ 60 years | 112[25] | ||||
| Lactoferrin | 2–9 years | 29[25] | |||
| ≥ 10 years | 4.6[25] | ||||
Also, feces may be analyzed for anyfecal occult blood, which is indicative of agastrointestinal bleeding.
A quick test for fecal contamination of water sources or soil is a check for the presence ofE. colibacteria performed with the help ofMacConkey agar plates orPetri dishes.E. coli bacteria uniquely develop red colonies at temperature of approximately 43 °C (109 °F) overnight. Although most strains ofE. coli are harmless, their presence is indicative of fecal contamination, and hence an increased possibility of the presence of more dangerous organisms.
Fecal contamination of water sources is highly prevalent worldwide, accounting for the majority of unsafe drinking water. Indeveloping countries most sewage is discharged without treatment. Even indeveloped countries events ofsanitary sewer overflow are not uncommon and regularly pollute theSeine River (France) and theRiver Thames (England), for example.
Diarrhea (or diarrhoea inBritish English) is the condition of having three or more loose or liquidbowel movements per day.[26] This condition can be a symptom of injury, disease, orfoodborne illness and is usually accompanied by abdominal pain. There are other conditions which involve some but not all of the symptoms of diarrhea, and so the formal medical definition of diarrhea involves defecation of more than 200 grams per day (though formal weighing of stools to determine a diagnosis is never actually carried out).
It occurs when insufficient fluid is absorbed by the colon. As part of the digestion process, or due to fluid intake, food is mixed with large amounts of water. Thus, digested food is essentially liquid prior to reaching the colon. The colon absorbs water, leaving the remaining material as a semisolid stool. If the colon is damaged or inflamed, however, absorption is inhibited, and watery stools result.
Diarrhea is most commonly caused by a myriad ofviral infections but is also often the result ofbacterial toxins and sometimes even infection. In sanitary living conditions and with ample food and water available, an otherwise healthy patient typically recovers from the common viral infections in a few days and at most a week. However, for ill or malnourished individuals diarrhea can lead to severedehydration and can become life-threatening without treatment.
Constipation refers to bowel movements that are infrequent or hard to pass.[27] Constipation is a common cause of painful defecation. Severe constipation includes obstipation (failure to pass stools or gas) andfecal impaction, which can progress tobowel obstruction and become life-threatening.
Bile overload is very rare, and not a health threat. Problems as simple as serious diarrhea may cause blood in one's stool. Black stools caused by the presence of blood usually indicate a problem in the intestines (the black color is a sign of digested blood), whereas red streaks of blood in stool usually are caused by bleeding in the rectum or anus.
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Human feces has historically been used asfertilizer for centuries in the form ofnight soil,fecal sludge, andsewage sludge. The use of untreated human feces in agriculture poses significant health risks and has contributed to widespread infection withparasitic worms—a disease calledhelminthiasis, affecting over 1.5 billion people in developing countries.
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There are methods available to safely reuse human feces inagriculture as per the "multiple barrier concept" described by theWorld Health Organization in 2006.[28] The approach to "close the loop" between human excreta (sanitation) and agriculture is also calledecological sanitation. It may involve certain types ofdry toilets such asurine-diversion dry toilets orcomposting toilets.
In humans, fecal transplants (orstool transplant) is the process of transplantation of fecal bacteria from a healthy individual into a recipient who has a certain disease, such asirritable bowel syndrome. The resultinginoculation of healthygut flora can sometimes improve the physiology of the recipient gut.
Fecal bacteriotherapy—also known as a fecal transplant—is a medical procedure wherein fecal bacteria are transplanted from a healthy individual into a patient.[29][30] Recent research indicates that this may be a valuable method to re-establish normal gut cultures that have been destroyed through the use of antibiotics or some other medical treatments.
Thebiogas produced from feces when it is contained insewage and treated in ananaerobic digestion process could be worth as much as US$9.5 billion.[31]
Washington DC plans to produce biogas fromsewage sludge, the by-product ofsewage treatment, which will save US$13 million a year.[32] Teams from the Cambridge Development Initiative, led by Stanford researcher Maisam Pyarali, began a project in 2015 to convert sewage from the slums ofDar Es Salaam into biogas and fertilizer with solar concentrators.[33]
Paleofeces, also known as coprolites (though that name is more commonly used in reference to animal feces), are ancient human feces, often found as part ofarchaeological excavations or surveys. Intact feces of ancient people may be found in caves in arid climates and in other locations with suitable preservation conditions. These are studied to determine the diet and health of the people who produced them through the analysis of seeds, small bones, and parasite eggs found inside. They also may be analyzed chemically for more in-depth information on the individual who excreted them, usinglipid analysis andDNA analysis. The success rate of usable DNA extraction is relatively high in paleofeces, making it more reliable than skeletal DNA retrieval.[34]
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In most human cultures, feces elicit varying degrees ofdisgust. Disgust is experienced primarily in relation to the sense of taste (either perceived or imagined) and, secondarily to anything that causes a similar feeling by sense of smell, touch, or vision. As such, human feces are regarded as something to be avoided diligently: expelled in private and disposed of immediately and without a trace. It often is considered an unacceptable topic in polite conversation and its mere mention may cause offence in certain contexts.
An example of repulsion by feces from the ancient world is found in the writings calledDeuteronomy used byJews andChristians:
Designate a place outside the camp where you can go to relieve yourself. As part of your equipment have something to dig with, and when you relieve yourself, dig a hole and cover up your excrement. For the LORD your God moves about in your camp to protect you and to deliver your enemies to you. Your camp must be holy, so that he will not see among you anything indecent and turn away from you.[35]
Evolution can explain this disgust since feces are a significant disease vector, carrying many kinds of microorganisms that can sicken humans, includingE. coli.
People from different cultures employ a variety of personal cleansing practices after defecation. Theanus andbuttocks may be either washed with liquids or wiped withtoilet paper or other solid materials. In manyMuslim,Hindu andSikh cultures, as well asSoutheast Asia and Southern Europe, water is usually used for anal cleansing using a jet, as with abidet, or most commonly, splashed and washed with the hand. In other cultures (such as manyWestern countries), cleaning after defecation is generally done withtoilet paper only.
There are many synonyms in informalregisters for human feces. Many areeuphemistic,colloquial, or both; some areprofane (such asshit), whereas most belong chiefly tochild-directed speech (such aspoo orpoop) or tocrude humor (such asturd). An example of an euphemistic term for feces isnumber two.
Human feces together with humanurine are collectively referred to ashuman waste or humanexcreta.
Media related toHuman feces at Wikimedia Commons