Talking about poop is never really pleasant, but it is sometimes necessary when it comes to being proactive about your digestive health. The size, shape, color, and consistency of your poop (or stool in medical terms) can, perhaps surprisingly, tell you a lot about the health of your gastrointestinal tract. Indeed, it can even be somewhat alarming to look down in the toilet and see a very different sight than you’re used to. One example of this is black or tarry stools.

How Does Digestion Work? 

To understand why stools may be a different color or consistency, it’s important to consider how the digestive process works. When chewed food reaches the stomach, muscles that surround the organ physically mash the food as digestive juices break it down into mostly liquid elements. This liquid, called chyme, makes its way into the small intestine where additional gastric juices introduce enzymes that break the food down on a molecular level and send vital nutrients around the body through the bloodstream.

The remaining semi-fluid waste materials and indigestible fiber enter the large intestine. As these materials are advanced through the various sections of the colon by intestinal muscles, water is gradually absorbed. Additionally, beneficial bacteria native to the colon feed on this material and produce valuable vitamins; these healthy bacteria also help break down fiber. When everything is functioning normally, a soft, firm, brown stool is formed that is easily passed during defecation. 

What Causes Black Stool or Tarry Stool?  

Unfortunately, things don’t always function normally. A wide range of factors can influence how stool appears, including diet, physical activity level, medication, or even an underlying medical condition. A commonly experienced deviation from the normal brown color is when the stool is black or has a tarry consistency. This is known as melena and is usually associated with upper gastrointestinal bleeding; in addition to the distinctive dark color, melena is recognizable by its foul-smelling odor. Below are some possible reasons for this phenomenon: 

  • Dark Foods: One of the most common causes of black stool is foods that are either naturally dark-colored or dark because of heavy food coloring. Some of the pigments in these foods aren’t digested and therefore show up in the stool, and it can look very similar to blood. Examples include: beets, chocolate, black licorice, and blueberries. All things being equal, stool should return to its normal color if you simply don’t eat such foods.   
  • Iron Supplements: Another common cause of black stool is taking iron supplements. Usually taken as a treatment for anemia, iron supplements may leave a dark color if some of it isn’t fully absorbed into the bloodstream. It may also look dark green.  
  • Peptic Ulcer: Peptic ulcers are breaks in the lining of the stomach or the small intestine that can cause bleeding in some cases. Blood that makes its way into the digestive tract will retain its color all the way through the formation of stool in the large intestine. When blood is mixed with other components, it can appear as very dark red or black in the toilet.  
  • Gastritis: Gastritis is the general term for an inflammation of the stomach lining. This kind of inflammation can be caused by smoking, alcohol, excessive use of over-the-counter painkillers, or an infection. In severe cases, bleeding may result and additionally appear in the stool.  
  • Bismuth: Bismuth subsalicylate (Pepto-Bismol) is used to treat a variety of gastrointestinal symptoms like indigestion or heartburn. When there are trace amounts of sulfur in the large intestine, the bismuth subsalicylate reacts with the sulfur and forms bismuth sulfide. This compound can temporarily turn stools black.  
  • Cancer: Another potential reason for gastrointestinal bleeding that can cause black stool is having either esophageal, gastric, or colorectal cancer. However, by the time cancer would be capable of causing the bleeding, there would also be a number of other prominent symptoms.
  • Inflammatory Bowel Disease (IBD): IBD is a common problem in gastroenterology, and the two principle examples are Crohn’s disease and ulcerative colitis. Inflammation of the intestinal lining and the presence of ulcers are two of the main causes of blood being present in poop.  
  • Hemorrhoids: When the veins that surround the anus become inflamed and swollen, they are called hemorrhoids. In addition to anal irritation and itching, one common symptom of hemorrhoids is bleeding; though usually this blood appears bright red, a more advanced or severe case may look black or tarry.
  • Esophageal Varices: Esophageal varices are essentially swollen veins located in the esophagus. This is typically seen as a symptom in people who have liver disease and can also lead to bleeding. 
  • Mallory-Weiss Tear: A Mallory-Weiss tear is the name for a tear in the lower esophagus that occurs because of violent vomiting or coughing. Such a traumatic tear can cause bleeding but usually heals on its own.  
  • Constipation: Constipation is the state of having infrequent bowel movements that are often also hard, dry, and difficult to pass. Sometimes excessive straining while defecating can cause blood vessels to burst in the rectum and anus and start bleeding.  

Treatment for Tarry Stool    

As noted, there are several causes of black stool that come from ingesting a particular food or medicine; the color is temporarily changed because of the presence of pigments or a chemical reaction. In either case, stools should return to normal as soon as it is out of your body. Most of the other potential reasons for black, tarry stools are related to gastrointestinal bleeding. In cases of bleeding, treatment will vary widely depending on any underlying conditions that can cause bleeding. Options typically include recommended dietary modifications or medication. 

When Should I Be Concerned?    

Seeing any kind of unusual stool color in the toilet can be alarming, but black stools that have that tarry consistency likely indicate bleeding as discussed above. Because many common causes are potentially very serious conditions, you should see a healthcare provider as soon as possible if you have tarry stool, have vomited blood, or feel lightheaded and dizzy. 

The appearance of your poop can sometimes give a good indication of the state of your digestive health. If you have been noticing color changes in your stools, including signs that it might be blood, you should make an appointment with a gastroenterologist. At Cary Gastro, we are passionate about helping you keep your digestive system healthy as a part of overall health and wellbeing. Contact us today for more information or to request an appointment.