Brown Poop with Black Chunks: 5 Causes & When to Worry.

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The presence of large black chunks or smaller black dots in stools is a common finding.

My patients always ask me about the cause of such a symptom.

The short answer is dietary changes and supplements in more than 90% of cases. However, these black chunks can also mean blood.

So, in this article, I’ll answer all your questions regarding the causes of black chunks in brown poop.


Table of Contents

What is the nature of black chunks in brown poop?

Black chunks in stool are often food particles. Many of the foods we eat every day may appear as black spots or chunks in our stool.

However, these black chunks can also be:

  • Iron (from iron supplements or iron-rich foods).
  • Artificial food colorings.
  • Medications such as Pepto-Bismol.
  • Blood (blood is processed (digested) into a black tarry-like substance inside the gut). Which can appear as black chunks in the brown stool.

Below in this article, you will learn how to differentiate between serious causes (such as blood) and everyday causes, such as food and beverages.

What are the main causes of black chunks in brown poop?

1. Dietary changes (commonest).

Dietary particles are the most common cause of black chunks in your brown poop. Many reddish, greenish, and dark foods appear as undigested black chunks.

This is the simplest and the most common cause of black dots or chunks. it is often temporary and related to what you ate in the previous 24-48 hours before the appearance of black chunks.

  • Iron in iron-containing foods:
    • Red meat,
    • Spinach,
    • beets,
    • kidney beans,
    • molasses,
    • and oysters.
  • Black-colored foods & fruits
    • Blueberries.
    • Blackberries.
    • Plums.
    • Black beans.
    • Figs.
    • Cherries.
    • Spices such as black pepper.
    • Bananas.
    • Dark puddings
  • Artificial food coloring: such as
    • black licorice.
    • Chocolate puddings.
  • Undigested seeds: such as strawberry seeds, sesame seeds, and guava seeds.
  • Green leafy vegetables: once digested, they turn dark green or black.
  • Tomatoes and tomato products.
  • Red wine.
  • Raw or undercooked meat: besides containing iron, it also contains some blood inside the meat fibers.

How to know if the black chunks are due to food:

  • It appears after consuming significant amounts of one or more of the above-listed foods.
  • It soon disappears after one or two days.
  • It is not associated with abnormal symptoms such as severe abdominal pain, or vomiting blood.
  • The stool is not entirely black but brown or slightly greenish-brown.
  • No diarrhea or tarry stools.
  • No signs of bleeding, such as shortness of breath, fast heartbeats, or fainting.
  • No noticeable changes in stool smell (no characteristic fishy smell).

You can also stop eating more of the above-mentioned offending foods and notice if the black chunks disappear. Consult your doctor if the black chunks don’t disappear or if bleeding is suspected (see later).

2. Iron Supplements.

Iron is an essential element for many body functions. The most common symptom of iron deficiency is anemia (low hemoglobin levels).

So, many people may take iron-containing supplements for the treatment or prevention of anemia.

Most supplements taken for general well-being contain a low concentration of iron. However, people with established anemia may take a high-concentration iron supplement.

These iron supplements (especially those with higher iron concentrations) may lead to brown dots or chunks in your stool.

Don’t stop taking iron supplements on your own if it is prescribed for anemia treatment. Consult your doctor at first, as it may lead to worsening anemia symptoms.

3. Peptic ulcer disease.

Bleeding peptic ulcers (stomach or duodenal ulcers) are the most common cause of blackish blood in the stool.

Unfortunately, 70% of peptic ulcers are painless. So, peptic ulcers may bleed without prior symptoms such as stomach pain.

However, it is more common for bleeding peptic ulcers to cause dark black and loose stool (tarry stool). However, black chunks in a brown stool can also occur.

Symptoms and signs of peptic ulcer bleeding:

  • Asymptomatic (no pain) in up to 70% of cases.
  • Chronic or recurrent upper stomach pain (in the middle of the stomach, above the belly button).
  • The pain is growing or burning in nature.
  • The pain is often triggered by certain fatty, spicy, and acidic foods.
  • The pain typically improves with antacids and acid-lowering medications.
  • Nausea or vomiting.
  • Anorexia (loss of appetite).
  • When the ulcer bleeds, it may lead to vomiting of blood (haematemesis) or passage of black tarry stools (melena).
  • Signs of anemia and shock may develop in severe cases: dizziness, shortness of breath, pallor, dizziness, fainting, or coma.

4. Pepto-Bismol® (Bisthmuth subsalicylates).

Pepto-Bismol is a drug that controls diarrhea, stomach pain, and other digestive issues. Recent intake of Pepto-Bismol may cause black stools or black chunks in a normal brown stool.

Typically, your stool with revert to its normal color within a day or two after the last dose of Pepto-Bismol. It is often not a cause of concern.

5. Coloanorectal Cancer.

Coloanorectal cancer is common among older age groups (particularly those 50 years and older).

The following illustration from shows the increased risk of coloanorectal cancer with age.

It is one of the most common cancers worldwide. Unfortunately, patients with coloanorectal cancer may remain asymptomatic or have minimal symptoms for long periods.

Bleeding for the cancer mass may cause reddish or blackish stool or black chunks in a normal brown stool.

So, it is important to be aware of the risk factors and the symptoms of such a disease.

Risk factors of coloanorectal cancer:

  • Positive family history of colon or anorectal cancer.
  • Being obese.
  • Diet high in red or processed meat.
  • Diabetes Mellitus at a young age.
  • Alcohol.
  • Tobacco smoking.
  • Physical inactivity.


  • Recurrent changes in bowel habits (constipation or diarrhea) are the most common symptom of coloanorectal cancer at diagnosis.
  • Blood in the stool (in 50% of the cases): sigmoid or anorectal cancer is more likely to cause red blood in the stool with no pain, but black chunks with brown stool also occur.
  • Bleeding from the early parts of the colon (the ascending and transverse colon is often darker in color or even black.
  • Sings of anemia include fatigue, shortness of breath with exertion, dizziness, and fast heartbeats.
  • Abdominal pain: isolated abdominal pain is rare with coloanorectal cancer.
  • A sense of mass in the rectum.
  • Weight loss.
  • Nausea, loss of appetite, unexplained fever.
  • Signs of cancer spreading to other organs (such as bone or liver pain) may also occur.

6. Inflammatory Bowel disease.

Inflammatory bowel disease is a common disease with unclear causes, such disease chronic inflammation, and ulceration of the digestive tract lining.

Two distinctive types of IBD:

  • Ulcerative colitis: inflammation and ulceration restricted to the colon and the rectum.
  • Crohn’s disease: inflammation and ulceration at any part of the digestive tract from the mouth to the anus.

Ulcerative colitis and Crohn’s disease can cause red or blackish stool or black chunks with normal brown stools.

Symptoms of IBD include:

  • Chronic or recurrent diarrhea.
  • Mucus and/or blood in the stool.
  • The blood can be either dark or bright red. Often mixed with mucus.
  • The bright red blood in stool is painful in most cases. Painless, bright red blood in the stool can occur but is less common.
  • Chronic abdominal pain.
  • Reduced appetite.
  • Weight loss.
  • Unexplained fever.
  • Anorexia.

7. Diverticular disease.

Diverticulae are sac-like projections arising from weak areas of the colon. The most common site of the diverticula is the sigmoid colon (the last part of the colon just before the rectum).

Diverticular disease is very common, and its incidence increases with age. For example, more than 60% of people above 60 have colon diverticula.

About 5 to 10% of people with diverticular disease may experience red (more common) or black (less common) chunks or spots in stool.

Pain occurs only when there is diverticular inflammation (diverticulitis). The most common site for diverticulitis pain is the lower-left abdomen (the site of the sigmoid colon).

Symptoms suggestive of diverticular bleeding:

  • Being older is a risk factor for diverticulitis.
  • Most cases of diverticular disease are asymptomatic (unless it bleeds or becomes inflamed).
  • 5 to 10% of people with diverticular disease experience painless, red blood in the stool. The bleeding may be massive and cause anemia symptoms or low blood pressure (shock).
  • Less commonly, it may present with dark redo or blackish speckles or chunks in the stool.
  • Discomfort or mild abdominal pain (commonly in the left lower abdomen but can occur elsewhere).
  • Inflammation of the diverticula (diverticulitis) has a more severe course with severe pain, fever, nausea, vomiting, and severe abdominal tenderness.

8. Other causes of bleeding in the gut.

Coloanorectal cancer, peptic ulcer disease, and diverticular disease are among the most common causes of red or black blood chunks in the stool.

However, Other less common conditions may cause bloody stool in the form of black chunks, including:

  • Bleeding colon or small intestinal polyp.
  • Esophageal and gastric varices (dilated veins) in patients with liver diseases such as liver cirrhosis.
  • Mallory-Weiss syndrome (an esophageal tear that bleeds due to vigorous vomiting).
  • Vascular malformations inside the gastrointestinal tract (the stomach, small intestine, or colon).
  • Rectal ulcers.
  • Piles and fissures.
  • Dysentery.
  • Pseudomembranous colitis due to clostridium difficile infection.
  • Parasitic infections such as Ascaris and tapeworms (cause minute bleeding).
  • Blood-thinning medications or blood-thinning diseases such as thrombocytopenia (low platelet count).

The illustration below shows the most common causes of gastrointestinal bleeding that may present with black stools or black chunks in the stool (reference).

How to know if the black chunks are blood? (when to worry)

Blood in the stool may appear red or blackish. The black stool often results from stomach, duodenal, or esophageal sources. However, intestinal and colonic blood sources may also lead to black stool or blackish chunks in poop.

The below signs, symptoms, and risk factors may help you differentiate blood from other causes of black chunks in brown stool:

  • The black chunks or pits may be mixed with dark or bright red blood spots.
  • Characteristic fishy or rotten-meat smell.
  • The stool may later turn completely black and loose (tarry stools).
  • Signs of bleeding include pallor, shortness of breath, fast heartbeats, or fainting.
  • Symptoms are suggestive of peptic ulcer disease, such as vomiting of blood, severe upper stomach pain, nausea, anorexia, etc.
  • Signs of coloanorectal cancer such as weight loss, persistent change of bowel habits, anemia, etc.

Frequently asked questions (FAQs).

Are black specks in stool parasite eggs?

No, black specks in stool are not likely to be parasite eggs. That’s because parasite eggs are often very tiny and not detectable by the naked eye. Parasite eggs need a microscope to be seen.

Why does my poop a mix of black and brown?

Your poop may have black chunks mixed with brown (normal) color. The most common cause of this color mix is often dietary factors, such as tomatoes, red meat, green vegetables, blueberries, etc. Other causes include blood or dark-colored medications and supplements such as iron.

What causes little black seeds in stool?

Your stool may contain little seeds that appear in black dots in the stools. It is often of dietary sources such as guava, strawberries, or bananas.