Blood in the stool may be visible, or it may be "occult," which means that it can only be detected by laboratory analysis. Visible blood may be bright red, maroon or (if it has passed through a large portion of your digestive tract) black. It is important to see your doctor if you see definite or suspected blood in your stool. Some conditions that can cause blood in or on the stool include:

Hemorrhoids

Anal fissures

Colon cancer

Diverticulosis

Peptic ulcer disease

Erosive gastritis

Esophagitis

Crohn's disease

Ulcerative colitis

Stomach cancer

Meckel's diverticulum

Bleeding varices

Nosebleed

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Black, Tar-Like Stool

Stools that appear dark and thick like tar are caused when blood has been in the digestive tract for several hours. Because this type of stool indicates internal bleeding, you should see your doctor as soon as possible. Disorders that can cause black, tarry stools are generally from upper gastrointestinal sources and include:

Peptic ulcer disease

Esophagitis

Gastritis

Stomach cancer

Bleeding varices

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Unusually Light Stool

Pale, greasy, usually foul-smelling stool is often indicative of digestive and absorption problems. The appearance is due to undigested fats that remain in the stool, or in some cases due to a lack of bilirubin in the intestines. Disorders that may cause pale or yellowed stool include:

Acute viral hepatitis

Alcohol and drug-induced hepatitis

Bile-duct disease

Cancer of gallbladder and bile ducts

Gluten sensitivity (celiac sprue)

Giardiasis

Bacterial overgrowth

Chronic pancreatitis

Chronic hepatitis

Cirrhosis

Crohn's disease

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Mucus Or Pus In Stool

Pus in the stool is evidence of inflammation with or without infection of the lower GI tract. Pus may be present in the stool of people with ulcerative colitis, Crohn's disease, infectious colitis or diverticulitis.

Mucus can be caused by inflammation or by any other irritation in the colon. It is common in people with irritable bowel syndrome. It is also a possible symptom of colon cancer.

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Dry, Hard Or Rough Stool

These are common symptoms of constipation. The changes may simply be related to lack of fiber or water in the diet. See above for the medical conditions that can cause constipation.