Also referred to as stool.

Feces are the solid or semisolid remains of the food that could not be digested or absorbed in the small intestine, and has been degraded by bacteria in the large intestine.

Stooling is a vital biological function that rids the body of bacteria, fiber, cells, water, and indigestible plant matter.


Stool frequency is between three times a day and every three days.

Feces contains bacteria, small amounts of metabolic waste products such as bacterially altered bilirubin, and the dead epithelial cells from the lining of the gut.

Feces is discharged through the anus during defecation.

Urine and feces together are called excreta.

Feces vary significantly in size, color, texture, according to the state of the diet, digestive system and general health.

Normally human feces are semisolid, with a mucus coating.

Harder and less moist feces can sometimes be seen, and this is a normal occurrence when a prior bowel movement is incomplete, and feces are returned from the rectum to the large intestine, where water is absorbed.

Preventing spreading of pathogens from human feces via the fecal�oral route, are the main goals of sanitation.

The Bristol stool scale is a medical aid designed to classify the form of human feces into seven categories.

The Bristol stool scale is a medical aid designed to classify the form of human feces into seven categories. 


The stool form depends on the time it spends in the colon.


Types 1 and 2 indicate constipation. 


Types 3 and 4 are optimal, as these are the easiest to pass. 


Types 5-7 are associated with increasing tendency to diarrhea or urgency.

The stool form depends on the time it spends in the colon.



Meconium refers to the newborn’s first feces.

Usually feces has a light to dark brown coloration.

Fecal color results from a combination of bile, and bilirubin derivatives of stercobilin and urobilin, derived from dead red blood cells.

Normally stool is semisolid, with a mucus coating.

Yellowing of feces can be caused by an infection known as giardiasis, and Gilbert’s syndrome, and may indicate that food is passing through the digestive tract relatively quickly.

Yellow stool can be found in people with gastroesophageal reflux disease.

Yellowing of feces can be caused by giardiasis, an anaerobic flagellated protozoan parasite that can cause severe and communicable yellow diarrhea. 

Pale or gray stool 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.

Anything that decreases bile output, causes the stool to be much lighter in color.

Black feces an be due to the presence of red blood cells that have been in the intestines long enough to be broken down by digestive enzymes.

Black feces due to gastrointestinal bleeding is known as melena.

Melena is typically due to bleeding in the upper digestive tract.

such as from a bleeding peptic ulcer.

Blood in the stool an be due to many conditions including: hemorrhoids, anal fissures, diverticulitis, colon cancer, and ulcerative colitis.

Melena can be observed after consuming foods that contain a substantial proportion of animal blood.

Black stools can also be caused by a number of medications, such as bismuth subsalicylate and dietary iron supplements, or foods such as beetroot, black liquorice, or blueberries.

Hematochezia is 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.

Hemorrhoids can also cause surface staining of red on stools.

Blue feces can occur with the use of blue coloring in the treatment of radiation with Prussian blue in  cesium, and thallium poisoning, and with consumption of products containing blue food dye, such as blue grape soda, can have the same effect.

Consumption of products containing blue food dye, or grape soda, can turn stool blue.

Silver or aluminum paint-like feces color can be a result of biliary obstruction combined with gastrointestinal bleeding from any source.

Carcinoma of the ampulla of Vater, can result in gastrointestinal bleeding and biliary obstruction, resulting in silver stool.

Green stool can be due to having large amounts of unprocessed bile in the digestive tract.

Green stool can occasionally be due to eating liquorice candy, as it is typically made with anise oil rather than liquorice herb, and from consuming excessive amounts of green dye.

Purple feces is a symptom of porphyria.

Feces have odor which can vary according to diet and health status.

Meat protein contains a lot of the sulfur-containing amino acid methionine, which is a precursor of the sulfur-containing odorous compounds.

Fecal odor is made up of odorific volatiles:

Methyl sulfides


dimethyl sulfide

dimethyl trisulfide

dimethyl disulfides

Benzopyrrole volatiles



Hydrogen sulfide is the most common volatile sulfur compound in feces.

Fecal odor is increased by:

Celiac disease

Crohn’s disease

Ulcerative colitis

Chronic pancreatitis

Cystic fibrosis

Intestinal infection


Short bowel syndrome

Attempts to reduce the odor of feces and flatus:

Activated charcoal

Bismuth subsalicylate


Herbs such as rosemary

Yucca schidigera

Zinc acetate

On average humans eliminate 128 g of feces per person per day with a pH value of around 6.6.

Feces contains around 75% water and the remaining solid fraction is 84�93% organic solids.

These organic solids consist of:

25-54% bacterial biomass

2-25% protein or nitrogenous matter

25% carbohydrate or undigested plant matter

2-15% fat.

Colon secretions, epithelial shedding and gut bacterial action add protein and fat, the proportions of which vary depend on many factors diet and body weight.

Remaining solids are composed of calcium and iron phosphates, intestinal secretions, small amounts of dried epithelial cells, and mucus.

Fecal pH is 6.6.

Undigested food may appear in the stool and include

seeds, nuts, corn, and beans, mainly because of their high dietary fiber content.


Undigested seeds can pass through the human digestive system, and later germinate: tomato plants in sewage sludge.

Beets may turn stool into different hues of red.

Food coloring in some processed foods, can cause unusual coloring of feces,

Stool analysis can be conducted to detect the presence of parasites such as pinworms and their eggs or to detect disease-spreading bacteria. 

A stool culture can be performed to identify specific pathogens in stool.

The main pathogens include:

Bacteroides species

Salmonella and Shigella





E. coli O157


Entamoeba histolytica

Intestinal parasites and their ova

A test for fecal contamination of water or soil is a check for the presence of E. coli bacteria performed with the help of MacConkey agar plates or Petri dishes. 



Most E. coli organism strains are harmless, their presence is indicative of fecal contamination.



Fecal contamination of water sources is highly prevalent worldwide.

The stool guaiac test and fecal immunologic tests can be conducted to detect the presence of blood in stool that is not apparent to the unaided eye.

DNA analysis of stool Cologuard can be utilized to diagnose colon abnormalities.

The feces can be analyzed for calprotectin levels an indicator of inflammatory process such as Crohn’s disease, ulcerative colitis and neoplasms.

Lactoferrin can be assessed in the feces as a determinant of the degree of inflammation.

Because neutrophils are a defining feature of acute inflammation, and elevated fecal calprotectin or lactoferrin are highly sensitive and specific for intestinal information from any cause.

Inflammation can be assessed via calprotectin or lactoferrin assays.

Fecal calprotectin and lactoferrin are antimicrobial peptides released by activated neutrophils, and neutrophils are the defining feature of acute inflammation.

Elevated calprotectin or lactoferrin in stools are highly sensitive and specific for intestinal inflammation from any cause: includes active colitis in inflammatory bowel disease and immune checkpoint inhibitor induced colitis


Diarrhea is the condition of having three or more loose or liquid bowel movements per day.

Diarrhea can be a symptom of injury, disease or foodborne illness and is usually accompanied by abdominal pain.

The formal medical definition of diarrhea involves defecation of more than 200 grams per day , though weighing of stools to determine a diagnosis is never actually carried out.Diarrhea occurs when insufficient fluid is absorbed by the colon.

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, absorption of water is inhibited, and watery stools result.

Diarrhea is most commonly caused viral infections but is also often the result of bacterial toxins and sometimes even infection.

Healthy patients typically recover from the common viral infections in a few days.

Constipation refers to bowel movements that are infrequent or hard to pass.

Less moist feces can sometimes become impacted in the distal end of the rectum, and  occurs  when a prior bowel movement is incomplete, and feces is returned from the rectum to the large intestine, where water is further absorbed.


Severe constipation includes obstipation and fecal impaction, which can progress to bowel obstruction and become life-threatening.


Constpation is a common cause of painful defecation. 


Stool cultures are performed to identify specific pathogens in stool. 


Common stool pathogens: 

Bacteroides species

Salmonella and Shigella





E. coli O157 


Entamoeba histolytica

Intestinal parasites.


The use of untreated human feces in agriculture poses significant health risks: infection with parasitic worms, a disease called helminthiasis, affecting over 1.5 billion people in developing countries.


Fecal transplants from a healthy individual into a recipient who is suffering from a certain disease, such as Clostridium difficile infection are now possible.

((Fecal microbiota transplantation)) is the process of transplantation of fecal bacteria from a healthy individual into a recipient who is suffering from a certain diseases.



The innoculation results in healthy gut flora and can sometimes improve the physiology of the recipient gut.



Fecal bacteriotherapy may re-establish normal gut flora that have been destroyed through the use of antibiotics or some other medical treatments.


Biogas can be produced by anaerobic digestion process of feces.

Leave a Reply

Your email address will not be published. Required fields are marked *