SYMPTOMS

What is black stool?

Broadly speaking, black stool refers to any stool that appears black in color, sometimes simply called "darkened stool."

Narrowly defined, black stool specifically refers to stool darkened by upper gastrointestinal bleeding, which is closely related to health issues ^[1]. (The upper gastrointestinal tract includes the oropharynx, esophagus, stomach, duodenum, etc.)

Black stool (Melena) can be further divided into Black stool and Tarry stool based on appearance. The former is dry and black, while the latter, also known as tarry stool, is wet and black, resembling tar. Of course, these distinctions are not absolute but rather a spectrum—some stools are drier, while others are wetter.

In addition to being black, black stool often has a shiny surface and a strong, distinct odor different from typical fecal smell—more like a mix of blood and feces but more pronounced, making it hard to forget once smelled ^[1].

Is black stool the same as bloody stool?

Bloody stool is a broader term than black stool, or black stool can be considered a type of bloody stool.

Any bleeding in the digestive tract that exits through stool is considered bloody stool. It has more causes, including upper gastrointestinal bleeding, lower gastrointestinal bleeding (e.g., colon, rectum, anal canal), and systemic diseases (e.g., leukemia, thrombocytopenic purpura). Bloody stool can appear bright red, dark red, or black.

However, black stool is typically caused by a significant amount of bleeding in specific upper gastrointestinal areas. Only bleeding in these regions can give stool its distinctive black color ^[2].

Why is black stool caused by upper gastrointestinal bleeding?

Blood is red, so why does stool turn black after gastrointestinal bleeding?

The red color of blood comes from hemoglobin in red blood cells, which contains ferric iron (Fe³⁺), giving it a red hue.

When blood enters the digestive tract, hemoglobin gradually breaks down. Under the influence of stomach acid, intestinal fluids, and gut bacteria, the iron combines with sulfides in the stool to form ferrous sulfide (FeS), turning it black and thus darkening the stool ^[3].

If black stool is abnormal, what color should stool normally be?

Normal adult stool is typically yellow to yellowish-brown. Infant stool is yellow or golden-yellow. The color mainly comes from bile staining. Greenish-yellow bile enters the intestines and gradually changes color as it moves through, eventually appearing yellow or brownish-yellow. The longer it stays in the intestines, the browner it becomes; the shorter the time, the more yellow it remains.

Although the food we eat can be colorful, food pigments are often unstable in digestive fluids. For example, common plant pigments like anthocyanins lose their original color by the time they are excreted. So, regardless of what you eat, stool is usually yellow to yellowish-brown.

Occasionally, eating large amounts of dark-colored foods can slightly alter stool color. Some exceptionally stable pigments, like betalains in red dragon fruit or beets, can even turn stool red. Don’t be alarmed if you see this.

If my stool is black, should I cry on the toilet?

No, no, don’t rush to cry yet.

You’ve only seen black stool, but whether it’s the dangerous kind requires further consideration. Many factors can cause black stool, not all of which are harmful.

Stay calm and figure it out first—then you can cry if needed.

TREATMENT

How to relieve black stool?

Relieving black stool is a false proposition. If we determine that the black stool is not caused by bleeding, then just let it be—it doesn’t affect appearance anyway.

If the black stool is due to bleeding or if you’re unsure of the cause, medical help is needed. In such cases, "relieving" black stool may require examinations and treatment.

If black stool is caused by a disease, how will doctors handle it?

Depending on the specific location and severity of the condition, doctors will choose different treatment methods. Below are some common diseases.

1. Bleeding caused by peptic ulcers
   • Medication: Drugs that inhibit gastric acid secretion, such as omeprazole and cimetidine, are often used. Antacids like aluminum hydroxide may also be prescribed.
   • Endoscopic treatment: Sometimes, direct hemostasis is performed via gastroscopy.
   • Other: If the above treatments are ineffective, interventional or surgical procedures may be considered.
2. Bleeding caused by esophageal or gastric varices
   • Medication: Drugs that reduce portal pressure, such as 14-peptide somatostatin and vasopressin, are often used for effective hemostasis.
   • Sengstaken-Blakemore tube: Placing this tube for compression can effectively control bleeding and is an emergency measure for severe cases unresponsive to medication.
   • Other: For severe cases, endoscopic, interventional, or surgical methods may also be chosen ^[4].

DIAGNOSIS

Which foods may cause black stools?

Here, black stools refer to the broad definition. Many foods and medications can darken your stool. For example:

1. Similar to the actual cause of black stools, consuming animal blood directly. The more duck blood, pork blood, etc., you eat, the darker your stool will appear.
2. Another special case is when a mother's nipple bleeds, and the baby swallows blood components while breastfeeding, which can also darken the baby's stool.
3. Even without blood, taking iron supplements can produce black stools due to the formation of black ferrous iron.
4. Apart from blood and iron, other medications or foods can directly darken stool. For example, drugs containing bismuth, medicinal charcoal, squid ink-stained rice, or excessive consumption of dark-colored foods like blueberries can deepen stool color, making it appear black.

When should black stools be a cause for concern? Under what circumstances should you seek medical attention?

Since there are many cases of false black stools, it's important to identify those caused by actual bleeding.

If you notice black stools, here's what you should do:

1. Review your recent medication use and diet—have you taken iron supplements, bismuth-based drugs, medicinal charcoal, or consumed animal blood, squid ink rice, or large amounts of dark-colored foods? If so, there may be no immediate cause for alarm.
2. Next, observe the stool's appearance. True black stools caused by upper gastrointestinal bleeding are typically shiny and black, not dull gray-black, and have a strong odor.
3. Finally, check for other symptoms. For example, recent dizziness, fatigue, palpitations, or excessive sweating may indicate anemia due to bleeding. Abdominal pain could signal diseases causing upper gastrointestinal bleeding. Vomiting blood is also a sign of upper gastrointestinal bleeding ^[4].

Which medical department should you visit for black stools?

Emergency department or gastroenterology.

What tests might be required for black stools?

Your doctor may ask you to fast before conducting tests such as fecal occult blood, complete blood count, gastroscopy, and, if necessary, ultrasound or DSA (digital subtraction angiography).

1. Fecal occult blood test: A lab test of stool samples. A positive result indicates gastrointestinal bleeding.
2. Complete blood count: Hemoglobin levels may drop during acute bleeding, aiding diagnosis.
3. Gastroscopy: Provides a clear view of the upper digestive tract. If bleeding is present, the source can be identified and treated directly.
4. Abdominal ultrasound: Rules out structural abnormalities, assisting in diagnosis and treatment ^[4].
5. DSA: A vascular imaging test using contrast agents to detect vascular abnormalities, mainly to identify gastrointestinal bleeding, gastric ulcers, duodenal ulcers, or vascular malformations in the small intestine.

Are black stools a sign of detoxification?

No.

Some "detox" supplement sellers claim their products cause black stools as proof of detoxification.

This specific type of black stool is usually caused by anthraquinone laxatives. Anthraquinones are compounds that stimulate the intestines to increase bowel movements, which can help with constipation. However, they also negatively affect intestinal mucosal cells, causing dark lipofuscin to accumulate. Prolonged use of anthraquinone laxatives can lead to blackened intestinal mucosa (see "melanosis coli"). When these cells shed into the stool, they darken it.

This "black stool" is not detoxification. While the long-term effects of lipofuscin deposits are unclear, there's no need to consume anthraquinone laxatives—especially overpriced detox supplements—for this purpose.

Can black stools indicate the amount of gastrointestinal bleeding?

Estimating upper gastrointestinal bleeding volume based on black stools is unreliable and only provides a rough assessment. For example:

1. Black stools may appear when daily bleeding exceeds 50–100 mL.
2. If accompanied by symptoms like palpitations, sweating, or fatigue, the bleeding may be severe, requiring urgent medical attention. Call emergency services if necessary and rest at home while waiting ^[4].

POTENTIAL DISEASES

What diseases can cause black stools?

We know that upper gastrointestinal bleeding can cause black stools, so identifying which diseases can lead to upper gastrointestinal bleeding is key. In China, common diseases that cause upper gastrointestinal bleeding include:

1. Peptic ulcers. More common in young people, chronic abdominal pain may occur before black stools appear.
2. Acute gastric mucosal lesions caused by alcohol or certain medications. Occurs after heavy alcohol consumption or the use of antiplatelet drugs like aspirin.
3. Upper gastrointestinal malignancies such as gastric cancer and esophageal cancer. More common in elderly individuals, black stools may appear without prior symptoms.
4. Esophageal and gastric varices. Often occurs in patients with cirrhosis, leading to massive black stools and often accompanied by hematemesis.
5. Mallory-Weiss tears. Occurs after severe vomiting, such as vomiting after alcohol consumption or induced vomiting ^[1].