Stool color provides insights into digestive health. While many variations are normal, dark-colored stool often prompts concern. This article explores common reasons for dark stool and outlines when to seek medical evaluation.
Understanding Stool Color Variations
Normal stool ranges from various shades of brown, primarily influenced by bile, a yellowish-green fluid from the liver that aids fat digestion. As bile moves through the digestive tract, enzymes alter it, changing its color from green to brown.
Dark stool can range from very dark brown to truly black. It is important to distinguish between dark brown stool, which is often benign, and “melena,” a medical term for black, tarry, and foul-smelling stool. Melena indicates the presence of digested blood and has a sticky, tar-like consistency.
Common Causes of Dark Stool
Many instances of dark stool are not concerning and stem from dietary factors or common medications. Consuming dark-colored foods can temporarily alter stool appearance. Examples include black licorice, blueberries, beets, dark leafy vegetables, and chocolate sandwich cookies. Artificial food colorings can also contribute to this temporary discoloration.
Certain medications and supplements also cause dark stools. Iron supplements are a frequent culprit; unabsorbed iron reacts with sulfur compounds in the gut to form black iron sulfide. Bismuth subsalicylate, found in medications like Pepto-Bismol, can also cause black stool when it reacts with sulfur in the digestive system to create bismuth sulfide. These changes are temporary and harmless, with stool color returning to normal within days of stopping the food or medication.
Serious Causes of Dark Stool
Melena, characterized by black, tarry, foul-smelling stool, indicates internal bleeding, most often from the upper gastrointestinal (GI) tract. The black color and tarry consistency result from digested blood interacting with digestive chemicals and stomach acid as it travels through the system. Upper GI bleeding involves the esophagus, stomach, and the first part of the small intestine (duodenum).
Several conditions can lead to upper GI bleeding and melena. Peptic ulcers, open sores in the stomach or duodenum lining, are a frequent cause. They can bleed due to Helicobacter pylori (H. pylori) infection or long-term nonsteroidal anti-inflammatory drug (NSAID) use.
Gastritis, inflammation of the stomach lining, can also cause bleeding. Esophageal varices, enlarged veins in the esophagus, are another serious cause, especially in individuals with liver disease, as these fragile veins can rupture. Other serious causes include Mallory-Weiss tears (esophageal tears from severe vomiting) and growths in the upper digestive tract.
When to Seek Medical Attention
While many cases of dark stool are benign, medical attention is necessary if it indicates melena, a sign of internal bleeding. Seek urgent medical care if dark stool is accompanied by other concerning symptoms.
These “red flag” symptoms include dizziness, lightheadedness, or fainting, which can signify significant blood loss. Severe abdominal pain, vomiting blood (which may appear red or like coffee grounds), a rapid heart rate, or unexplained weight loss also require immediate medical consultation. Consult a healthcare provider if persistent dark stool occurs or if any of these accompanying symptoms are present, even if a benign cause is suspected.