Black stool can be alarming, but most causes are harmless. Temporary cases of black stool are typically due to food intake or iron supplements. If black stool persists, it can signify bleeding in the digestive tract caused by conditions like ulcers, hemorrhoids, infections, or cancer.
Some other potential causes include medication side effects and diseases that affect digestion. Let’s explore the common reasons for black poop and when to see a doctor.
Foods and Supplements
Foods high in dark pigments or iron supplements can temporarily turn stool very dark or black. Common culprits include:
- Black licorice – Contains anthocyanins that turn stool black. The effect should go away once you stop eating it.
- Blueberries – The skin of blueberries contains anthocyanins that could cause black stool.
- Iron supplements – Iron can make stool appear black. This is harmless but can be alarming if you forgot you took an iron pill.
- Activated charcoal – Taken for things like intestinal gas, activated charcoal binds to chemicals in stool and turns it black. This is temporary.
- Black foods with dark pigments like black beans, black sesame seeds, black food coloring, or dark beer. For dark greens like spinach, stool is more likely to turn green than black.
The black color from foods and supplements will resolve in a day or two after stopping intake. If it persists longer than this, see your doctor.
Bleeding in the Upper Digestive Tract
One alarming cause of black stool is bleeding somewhere in the upper digestive tract. Sources include:
- Gastric ulcers – Damage to the lining of the stomach or first part of the small intestine causes bleeding into the gut.
- Esophageal varices – These swollen veins in the esophagus may bleed, often due to liver cirrhosis.
- Cancer – Tumors in the esophagus, stomach, or small intestine can bleed into the digestive tract.
- Mallory Weiss tear – Vomiting or violent coughing can cause small tears in the esophagus which bleed.
- Other less common sources of upper gastrointestinal bleeding could include vascular malformations or a tear in the intestine called a Dieulafoy lesion.
Bleeding from the upper digestive tract takes a while to reach the rectum, so stool may not appear black until a day or two after the bleeding event. See a doctor right away if you vomit blood or have black stool along with symptoms like lightheadedness, chest pain, fever, or abdominal pain.
Bleeding in the Lower Digestive Tract
The other major cause of black stool is bleeding from the lower digestive tract – typically the colon, rectum, or anus. Potential sources include:
- Hemorrhoids – Swollen veins in the anus or rectum can bleed occasionally, causing black stool. Straining with constipation may worsen hemorrhoid bleeding.
- Anal fissures – Tears in the anus from passing hard stool can bleed and make stool appear black.
- Diverticula – Small pouches bulging from the colon may become inflamed and bleed occasionally.
- Colon polyps or cancer – Growths in the colon often bleed intermittently, which could cause black stool. Always get rectal bleeding evaluated promptly.
- Angiodysplasia – Abnormal blood vessels in the colon can rupture and bleed. This is more common in older adults.
- Colitis – Inflammation of the colon from infections, inflammatory bowel disease, or ischemia can damage the colon lining and make it bleed.
- Post-polypectomy bleeding – Removing large colon polyps carries a risk of bleeding afterward.
Stool will typically turn black quickly, within a day, with bleeding in the lower GI tract. Seek medical care if you have black stool along with symptoms like abdominal pain, diarrhea, or rectal pain.
Some medications can make stool appear black by binding bile pigments. These include:
- Iron supplements – In addition to adding iron to stool, iron pills can make stool black by binding to bile pigments.
- Bismuth subsalicylate – The active ingredient in products like Pepto-Bismol, bismuth turns stool black by binding bile.
- Other drugs linked to black stool include antibiotics, antipsychotics, and antacids containing aluminum hydroxide.
Illnesses Affecting Digestion
A few illnesses that affect the digestive process can also contribute to black stool:
- Cirrhosis – Scarring of the liver reduces bile production, which makes stool appear darker and tarry.
- Pancreatic cancer – By blocking pancreatic ducts, tumors prevent digestive enzymes from reaching the intestine, which can result in black stool.
- Gallbladder cancer – Tumors may obstruct bile ducts, causing less bile to reach the intestine and very dark stool.
- Small bowel bacterial overgrowth – Excess bacteria in the small intestine interfere with normal digestion, including bile salt absorption, resulting in black stool.
When to See a Doctor If You’re Suffering With Black Stool
Occasional black stool caused by a specific food or supplement you ate is not a cause for concern. But seek prompt medical attention if you have black stool along with:
- Bleeding – Vomiting blood or visible blood in stool
- Lightheadedness, dizziness, fatigue – Signs of blood loss
- Fever, chills, or abdominal pain – Indicates infection or inflammation
- Persistent diarrhea – Can accompany infections, food poisoning, or inflammatory bowel disease
- Unintentional weight loss – Potential sign of cancer or chronic illness
- Family history of cancer – Higher risk for colon cancer or polyps at a young age
Black stool that persists more than 2 days after stopping iron pills or other supplements should also be evaluated by a doctor.
While black stool is often harmless, the cause needs to be determined. Bleeding in the GI tract could be due to ulcers, growths, or tears that may require treatment.
Prompt diagnosis could also identify a serious condition like cancer early, improving outcomes. Keep an eye on stool color and notify your doctor about any concerning changes.
- Foods that can cause black stool:
- Upper gastrointestinal bleeding:
- Lower gastrointestinal bleeding:
- Digestive illnesses: