Human feces

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Human feces (or faeces; Latin: fæx), also known as stool,[1] is the waste product of the human digestive system including bacteria. It varies significantly in appearance, according to the state of the digestive system, diet and general health. Normally stool is semisolid, with a mucus coating. Small pieces of harder, less moist feces can sometimes be seen impacted on the distal (leading) end. This is a normal occurrence when a prior bowel movement is incomplete, and feces are returned from the rectum to the intestine, where water is absorbed. Meconium (sometimes erroneously spelled merconium) is a newborn baby's first feces.

Color variations[edit]

Human fecal matter varies significantly in appearance, depending on diet and health.

Human feces ordinarily has a light to dark brown coloration, which results from a combination of bile and bilirubin that is derived from dead red blood cells. Normally it is semisolid, with a mucus coating.
Yellowing of feces can be caused by an infection known as Giardiasis, which derives its name from Giardia, an anaerobic flagellated protozoan parasite that can cause severe and communicable yellow diarrhea. Another cause of yellowing is a condition known as Gilbert's Syndrome. Yellow stool can also indicate that food is passing through the digestive tract relatively quickly. Yellow stool can be found in people with GERD gastroesophageal reflux disease.
Pale or Clay
Stool that is pale or grey may be caused by insufficient bile output due to conditions such as cholecystitis, gallstones, giardia parasitic infection, hepatitis, chronic pancreatitis, or cirrhosis. Bile salts from the liver give stool its brownish color. If there is decreased bile output, stool is much lighter in color.
Black or Red
Feces can be black due to the presence of red blood cells that have been in the intestines long enough to be broken down by digestive enzymes. This is known as melena, and is typically due to bleeding in the upper digestive tract, such as from a bleeding peptic ulcer. Conditions that can also cause blood in the stool include hemorrhoids, anal fissures, diverticulitis, colon cancer, and ulcerative colitis. The same color change can be observed after consuming foods that contain a substantial proportion of animal blood, such as black pudding or tiết canh. Black feces can also be caused by a number of medications, such as bismuth subsalicylate (the active ingredient in Pepto-Bismol), and dietary iron supplements, or foods such as beetroot, black liquorice, or blueberries.[2]
Hematochezia is similarly the passage of feces that are bright red due to the presence of undigested blood, either from lower in the digestive tract, or from a more active source in the upper digestive tract. Alcoholism can also provoke abnormalities in the path of blood throughout the body, including the passing of red-black stool.
Prussian blue, a coloring used in the treatment of radiation, cesium, and thallium poisoning, can turn the feces blue. Substantial consumption of products containing blue food dye, such as blue curaçao or grape soda, can have the same effect.[3]
A tarnished-silver or aluminum paint-like feces color characteristically results when biliary obstruction of any type (white stool) combines with gastrointestinal bleeding from any source (black stool). It can also suggest a carcinoma of the ampulla of Vater, which will result in gastrointestinal bleeding and biliary obstruction, resulting in silver stool.[4]
Feces can be green due to having large amounts of unprocessed bile in the digestive tract and strong-smelling diarrhea. This can occasionally be the result from eating liquorice candy, as it is typically made with anise oil rather than liquorice herb and is predominantly sugar. Excessive sugar consumption or a sensitivity to anise oil may cause loose, green stools.[5]
Violet or Purple
Violet or Purple feces is a symptom of porphyria.


Feces possess physiological odor, which can vary according to diet (especially the amount of meat protein e.g., methionine)[6][7][8][9][10] and health status. The odor of human feces is suggested to be made up from the following odorant volatiles:[7]

(H2S) is the most common volatile sulfur compound in feces.[7] The odor of feces may be increased in association with various pathologies, including:[11]

Attempts to reduce the odor of feces (and flatus) 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:

Personal hygiene[edit]

Main article: Anal cleansing

Cultures employ a variety of personal cleansing practices after defecation.

Bristol stool scale[edit]

Main article: Bristol stool scale
Bristol stool chart.svg

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 the University of Bristol and was first published in the Scandinavian Journal of Gastroenterology in 1997.[17] The form of the stool depends on the time it spends in the colon.[18]

The seven types of stool are:

  1. Separate hard lumps, like nuts (hard to pass)
  2. Sausage-shaped but lumpy
  3. Like a sausage but with cracks on the surface
  4. Like a sausage or snake, smooth and soft
  5. Soft blobs with clear-cut edges
  6. Fluffy pieces with ragged edges, a mushy stool
  7. Watery, no solid pieces. Entirely Liquid

Types 1 and 2 indicate constipation. Types 3 and 4 are optimal, especially the latter, as these are the easiest to pass. Types 5–7 are associated with increasing tendency to diarrhea or urgency.[18]

Fecal markers[edit]

The 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 as Crohn's disease, ulcerative colitis and neoplasms (cancer).

Reference ranges for fecal markers
MarkerPatient typeUpper limitUnit
Calprotectin2–9 years166[19]µg/g of feces
10–59 years51[19]
≥ 60 years112[19]
Lactoferrin2–9 years29[19]
≥ 10 years4.6[19]

Also, feces may be analyzed for any fecal occult blood, which is indicative of a gastrointestinal bleeding.


Stool analysis (stool sample)[edit]

The main pathogens that are commonly looked for in feces include:

Intestinal parasites and their ova (eggs) can sometimes be visible to the naked eye.

Undigested food remnants[edit]

Undigested objects such as seeds can pass through the human digestive system, and later germinate. One result of this is tomato plants growing where sewage sludge has been used as fertilizer.


Main article: Diarrhea

Diarrhea is the condition of having three or more loose or liquid bowel movements per day.[20] This condition can be a symptom of injury, disease or foodborne 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 myriad viral infections but is also often the result of bacterial 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 severe dehydration and can become life-threatening without treatment.


Main articles: Humanure and Composting toilet

Fecal contamination[edit]

A quick test for fecal contamination of water sources or soil is a check for the presence of E. coli bacteria performed with the help of MacConkey agar plates or Petri dishes. E. coli bacteria uniquely develop red colonies at temperature of approximately 43 °C (109 °F) overnight. Although most strains of E. 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. In developing countries most sewage is discharged without treatment. Even in developed countries events of sanitary sewer overflow are not uncommon and regularly pollute the Seine River (France) and the River Thames (England), for example.

See also[edit]



  1. ^ Sometimes but not always stools in UK English; plural use not even mentioned in Oxford online dictionaries
  2. ^ Heller, JL (2009-11-01). "Bloody or tarry stools". National Institutes of Health. Retrieved 2009-11-30. 
  3. ^ "Fact Sheet: Prussian Blue". Centers for Disease Control and Prevention. 2006-05-10. Retrieved 2009-11-30. 
  4. ^
  5. ^
  6. ^ Hiele, M; Ghoos, Y; Rutgeerts, P; Vantrappen, G; Schoorens, D (June 1991). "Influence of nutritional substrates on the formation of volatiles by the fecal flora.". Gastroenterology 100 (6): 1597–602. PMID 2019366. 
  7. ^ a b c Tangerman, A (Oct 15, 2009). "Measurement and biological significance of the volatile sulfur compounds hydrogen sulfide, methanethiol and dimethyl sulfide in various biological matrices.". Journal of chromatography. B, Analytical technologies in the biomedical and life sciences 877 (28): 3366–77. doi:10.1016/j.jchromb.2009.05.026. PMID 19505855. 
  8. ^ Chavez, C; Coufal, CD; Carey, JB; Lacey, RE; Beier, RC; Zahn, JA (June 2004). "The impact of supplemental dietary methionine sources on volatile compound concentrations in broiler excreta.". Poultry science 83 (6): 901–10. doi:10.1093/ps/83.6.901. PMID 15206616. 
  9. ^ Geypens, B; Claus, D; Evenepoel, P; Hiele, M; Maes, B; Peeters, M; Rutgeerts, P; Ghoos, Y (July 1997). "Influence of dietary protein supplements on the formation of bacterial metabolites in the colon.". Gut 41 (1): 70–6. doi:10.1136/gut.41.1.70. PMC 1027231. PMID 9274475. 
  10. ^ Otto, ER; Yokoyama, M; Hengemuehle, S; von Bermuth, RD; van Kempen, T; Trottier, NL (July 2003). "Ammonia, volatile fatty acids, phenolics, and odor offensiveness in manure from growing pigs fed diets reduced in protein concentration.". Journal of animal science 81 (7): 1754–63. PMID 12854812. 
  11. ^ Dugdale, David C. ""Stools - foul smelling" on Medline Plus". U.S. National Library of Medicine. Retrieved 21 October 2012. 
  12. ^ Levine, J; Ellis, CJ; Furne, JK; Springfield, J; Levitt, MD (January 1998). "Fecal hydrogen sulfide production in ulcerative colitis.". The American journal of gastroenterology 93 (1): 83–7. doi:10.1111/j.1572-0241.1998.083_c.x. PMID 9448181. 
  13. ^ Bartlett, John G.; Gerding, Dale N. (15 January 2008). "Clinical Recognition and Diagnosis of Infection". Clinical Infectious Diseases 46 (s1): S12–S18. doi:10.1086/521863. 
  14. ^ Suarez, FL; Furne, J; Springfield, J; Levitt, MD (January 1999). "Failure of activated charcoal to reduce the release of gases produced by the colonic flora.". The American journal of gastroenterology 94 (1): 208–12. doi:10.1111/j.1572-0241.1999.00798.x. PMID 9934757. 
  15. ^ Suarez, FL; Furne, JK; Springfield, J; Levitt, MD (May 1998). "Bismuth subsalicylate markedly decreases hydrogen sulfide release in the human colon.". Gastroenterology 114 (5): 923–9. doi:10.1016/s0016-5085(98)81700-9. PMID 9558280. 
  16. ^ a b Giffard, CJ; Collins, SB; Stoodley, NC; Butterwick, RF; Batt, RM (Mar 15, 2001). "Administration of charcoal, Yucca schidigera, and zinc acetate to reduce malodorous flatulence in dogs.". Journal of the American Veterinary Medical Association 218 (6): 892–6. doi:10.2460/javma.2001.218.892. PMID 11294313. 
  17. ^ Lewis SJ, Heaton KW (1997). "Stool form scale as a useful guide to intestinal transit time". Scand. J. Gastroenterol. 32 (9): 920–4. doi:10.3109/00365529709011203. PMID 9299672. 
  18. ^ a b "Constipation Management and Nurse Prescribing: The importance of developing a concordant approach" (PDF). Archived from the original on 2006-07-05. Retrieved 2006-11-06. 
  19. ^ a b c d e Joshi, S.; Lewis, S. J.; Creanor, S.; Ayling, R. M. (2009). "Age-related faecal calprotectin, lactoferrin and tumour M2-PK concentrations in healthy volunteers". Annals of Clinical Biochemistry 47 (Pt 3): 259–263. doi:10.1258/acb.2009.009061. PMID 19740914.  edit
  20. ^ "Diarrhoea". World Health Organization. 

External links[edit]