Black Stool: A Comprehensive Guide to Causes and Treatments

Dark-colored foods and medications are some of the most common—and harmless—causes of black stool. Foods with black or dark-blue dyes, such as licorice or cupcakes with dark frosting, can temporarily change stool color. Iron supplements and medications containing bismuth, like Pepto-Bismol, are also frequent culprits. These causes don’t require treatment, but if black stool persists or has a strong, tar-like odor, it could point to something more serious.

If black stool lasts more than a day or two and has an especially foul, tar-like smell, internal bleeding may be to blame. Common sources include peptic ulcers in the stomach or esophagus or inflammation from gastritis. In these cases, blood mixes with the stool as it travels through the digestive tract, causing the darker color. A doctor can confirm the presence of blood through a stool test and may recommend further investigation to determine the source.

Bleeding higher up in the gastrointestinal tract—such as in the stomach or esophagus—can darken stool, while bleeding in the lower tract usually appears as bright red. Conditions like esophageal or stomach cancer can sometimes cause black stool early on, even before other symptoms appear. Because of this, persistent changes in stool color should always be evaluated by a healthcare provider.

When stool turns black due to blood, it often has a sticky consistency and an unusually strong odor. The color change usually requires a significant amount of blood or pigment from foods or medications. If you notice black, tar-like stool with other symptoms like dizziness, abdominal pain, or fatigue, it’s important to seek medical advice quickly. A physical exam, stool test, or imaging may be needed to find the cause.

It’s completely normal for newborns to pass black stool in their first few days of life. This early stool is called meconium, and it consists of materials the baby ingested in the womb—like amniotic fluid, bile, and shed intestinal cells. Meconium is thick, sticky, and dark green to black in color. After a few days, a baby’s stool should transition to yellow or brown as feeding begins and digestion kicks in.

Bismuth subsalicylate, an ingredient in over-the-counter medications like Pepto-Bismol, can temporarily turn stool black. This happens when the bismuth combines with sulfur in the digestive tract, creating a harmless dark compound. While this discoloration is not dangerous, it can be alarming if unexpected. If black stool persists after stopping the medication—or if other symptoms develop—it’s best to consult a doctor.

Ulcers are small internal sores that develop in the stomach, small intestine, or esophagus. When an ulcer becomes irritated or bursts, it can cause internal bleeding. When this occurs in the digestive tract, the blood that passes through the small intestine and mixes with feces can make subsequent bowel movements black.

Esophageal varices is a medical condition caused by abnormal veins in the esophagus. If the veins become irritated, they may begin to bleed. The blood is digested and travel through the digestive system, eventually being excreted, which will turn the stool black. Esophageal varices require medical attention, and a doctor may prescribe medications or procedures to address the problem.

Necrotizing enterocolitis is a life-threatening condition caused by infection and inflammation of the intestine. It affects infants, and premature babies are more likely to develop it. Symptoms include dark or bloody stools, a swollen belly, chills and fever, and fast heartbeat and breathing. This condition requires hospitalization and treatment as soon as possible.

The first thing one should do when they pass black stool is to determine whether any foods or drinks might have caused the occurrence. If one continues to pass black stool for multiple days or if pain or cramping accompanies bowel movements, the individual should seek medical attention.