feces
Meaning of feces: Color carries most of the information, since bile pigment explains brown, its absence explains pale, and digested blood explains black.
Definition of feces
Feces is the solid waste passed from the digestive tract during a bowel movement. It is mostly water, and the solid portion consists of bacteria, undigested fiber, fat, protein, cells shed from the gut lining, mucus and bile pigments. The characteristic brown color comes from those pigments after resident bacteria have chemically altered them during passage through the colon.
How is it formed?
What leaves the small intestine is liquid. The colon reclaims most of the water and salt from it over many hours, and the residue is compacted as it moves toward the rectum. Transit time governs consistency almost entirely: material hurried through stays loose because the water has not been absorbed, while material held too long becomes hard and dry. The bacterial population of the gastrointestinal tract makes up a large share of the solid weight, ferments fiber the body cannot digest, and produces gases and short-chain fatty acids as it does so.
What do changes in appearance indicate?
| Appearance | What it suggests |
|---|---|
| Pale or clay-colored | Bile is not reaching the bowel, as when a duct is blocked |
| Black and tarry | Blood digested on its way down, from the stomach or upper bowel |
| Bright red | Bleeding lower down, from the colon, rectum or hemorrhoids |
| Greasy, floating, foul-smelling | Fat is not being absorbed, as in pancreatic or coeliac disease |
| Persistently narrow or altered habit | A change in the bowel itself, warranting assessment |
Harmless explanations are common as well: iron tablets and bismuth darken stool, and beetroot reddens it. A single unusual bowel movement means far less than a pattern that persists.
What is a stool sample used for?
Because the material has traveled the entire digestive tract, it carries evidence from all of it. A laboratory test may look for hidden blood, which is the basis of bowel cancer screening programs, or culture bacteria and detect viruses and parasites in prolonged diarrhea. Calprotectin, a protein released by inflammatory cells, helps distinguish inflammatory bowel disease from irritable bowel syndrome. Fat content assesses absorption, and toxin testing identifies Clostridioides difficile after antibiotic use. Sampling requires no preparation, which is part of why it remains so widely used.
Also known as
Used in a sentence
A stool sample was collected to test the feces for signs of infection.
Good to know
A change in the color or consistency of feces, such as unusually pale or dark stool, can reflect a specific underlying process, which is why such changes are often described precisely when reported to a clinician.
Word origin
Where “feces” comes from
From Latin faeces, meaning dregs or sediment, the plural of faex.