Volume of the stool depends on the amount the person eats and the nature of the diet. For example, a diet high in roughage produces more feces than a soft, bland diet. Consistently large diarrheal stools suggest a disorder in the small bowel or proximal colon; small, frequent stools with urgency to pass them suggest a disorder of the left colon or rectum.
Color
Infant: Yellow to brown Adult: Brown
The brown color of the stool is due to stercobilin, a bile pigment derivative. The rapid rate of peristalsis in the breastfed infant causes the stool to be yellow. Stool color is influenced by diet. For example, the stool will be almost black if the person eats red meat and dark green vegetables, such as spinach. The stool will be light brown if the diet is high in milk and milk products and low in meat. The absence of bile may cause the stool to appear white or clay colored. Certain drugs influence the color of the stool. For example, iron salts cause the stool to be black. Antacids cause it to be whitish. Bleeding high in the intestinal tract causes a stool to be black due to the digestion of the blood. Bleeding low in the intestinal tract results in fresh blood in the stool. The stool darkens with standing.
Odor
Pungent; may be affected by foods ingested.
The characteristic odor of the stool is due to indole and skatole, caused by putrefaction and fermentation in the lower intestinal tract. Stool odor is influenced by its pH value, which normally is neutral or slightly alkaline. Excessive putrefaction causes a strong odor. The presence of blood in the stool causes a unique odor.
Consistency
Soft, semisolid, and formed
Stool consistency is influenced by fluid and food intake and gastric motility. The less time stool spends in the intestine (or the shorter the intestine), the more liquid the stool. Many pathologic conditions influence consistency.
Shape
Formed stool is usually about 1 inch (2.5 cm) in diameter and has the tubular shape of the colon, but may be larger or smaller, depending on the condition of the colon.
A gastrointestinal obstruction may result in a narrow, pencil-shaped stool. Rapid peristalsis thins the stool. Increased time spent in the large intestine may result in a hard, marble-like fecal mass.
Constituents
Waste residues of digestion: bile, intestinal secretions, shed epithelial cells, bacteria, and inorganic material (chiefly calcium and phosphates); seeds, meat fibers, and fat may be present in small amounts.
Internal bleeding, infection, inflammation, and other pathologic conditions may result in abnormal constituents. These include blood, pus, excessive fat, parasites, ova, and mucus. Foreign bodies also may be found in the stool.