How to Read Bloody Stools and Changes in Stool Color

If you see blood in stools, your first instinct may be to ignore it and wait for it to go away. This is particularly true if the bleeding seems incidental.

And, while you may be right and everything is perfectly fine, it is important that you take the time to look and assess what is actually happening. The very appearance of a stool can give you pretty strong clues as to the cause and origin of any bleeding.

What Stool Color Tells Us

Bloody stools often are a sign of a problem in the digestive tract, originating at any point on the journey from the mouth to the rectum. Coloration plays a huge part in pinpointing where the problem is and can generally be interpreted as follows:

• Darker stools suggest that the bleeding has taken place higher up in the gastrointestinal tract. As the stool slowly moves through the small and large intestines, any collected blood has time to coagulate and darken. Melena is the term used to describe black, tarry stools.
• Brighter, redder stools suggest that the bleeding is at the lower end of the gastrointestinal tract as the blood is fresh. Hematochezia is the term that refers to the passage of blood by the anus whether directly or on stools.
• Sudden, profound changes in stool color that return quickly to normal suggest that the problem may be something you ate. For example, eating licorice, iron supplements, Pepto-Bismol, or blackberries can cause purple-ish to black-colored stools while eating beets can definitely turn your stools a striking red. 

• While pale, chalky stools don't suggest bleeding, they are a definite sign of a liver problem such as hepatitis. The appearance of these stools is often accompanied by a yellowing of the skin or eyes (called jaundice).

Causes of Bloody Stools

If food and medication have been ruled out as causes of stool discoloration, you can start to consider other sources and causes of bleeding.

If stools are black and tarry, causes may include:

• Peptic ulcer
• Trauma
• A tear in the esophagus caused by violent vomiting
• Bleeding caused by inflammation of the stomach lining (gastritis)
• Restriction of blood flow to the large intestines caused by injury or inflammation (ischemic colitis)
• Infections that cause severe esophageal ulcerations (usually in immune-compromised persons)
• Cirrhosis which causes a blockage of blood flow to the liver and the widening of veins in the esophagus or stomach (called varices)
• Stomach cancer
• Esophageal cancer

If stools are maroon to bright red, causes may include:

• Diverticulosis (development of abnormal pouches in the colon)
• Hemorrhoids
• Colon cancer
• Non-cancerous growths such as polyps
• Bacterial infections (bacterial enterocolitis) such as salmonella and E. coli
• Inflammatory bowel diseases including Crohn's disease and ulcerative colitis
• Recent trauma including those caused by medical procedures such as colonoscopy
• Restriction of blood flow to the small intestines caused by injury (​mesenteric ischemia)
• Use of non-steroidal anti-inflammatory drugs (NSAIDs) such as aspirin and ibuprofen

See your doctor if you notice blood in your stool or experience changes in the color, consistency, or frequency of your bowel movements.

This is especially true if movements are accompanied by abdominal pain, fever, profuse anal bleeding, persistent pencil thin stools, or the vomiting of blood or a coffee ground-like grit (hematemesis).