What causes black, foul-smelling stool?
Mar 17, 2025
Source: Cainiu Health
Dr. Shen Yonghua
Introduction
In general, black and foul-smelling stool may be caused by factors such as diet, constipation, upper gastrointestinal bleeding, intestinal infection, or gallstones. Symptomatic management typically involves general treatment and medication. In daily life, it is recommended to maintain good living habits, eat a healthy diet, and avoid consuming spicy or irritating foods to help maintain gastrointestinal health.
In general, black and foul-smelling stool may be caused by dietary factors, constipation, upper gastrointestinal bleeding, intestinal infection, gallstones, and other reasons. Symptomatic treatment such as general management and medication might be required. If experiencing any discomfort, it is important to visit a hospital for examination and treatment as soon as possible. A detailed explanation is as follows:
1. Dietary factors
Consumption of large amounts of animal blood, liver, or foods with a strong odor such as garlic and onions may lead to chemical reactions between their components and substances in the intestines, causing the stool to become black and smelly. This is a normal physiological phenomenon, usually without other symptoms. After reducing the intake of these foods, stool color and odor typically return to normal.
2. Constipation
When stool remains in the intestine for a prolonged period, excessive water is absorbed, resulting in dry and hard stool. The bacteria in the intestine excessively ferment and decompose the dry stool, producing a foul odor. Additionally, the dry stool may rub against the intestinal mucosa, causing minor bleeding that turns the stool black. It is recommended to increase dietary fiber intake, drink more water, and engage in appropriate physical activity, which can help improve stool color and odor.
3. Upper gastrointestinal bleeding
Upper gastrointestinal bleeding caused by conditions such as gastric or duodenal ulcers can lead to black, tarry stools with a foul odor. This may be accompanied by symptoms such as vomiting blood, anemia, or abdominal pain. Immediate medical attention is advised, and treatment under a doctor's guidance with medications such as esomeprazole magnesium enteric-coated tablets, rabeprazole sodium enteric-coated tablets, or lansoprazole tablets may be necessary.
4. Intestinal infection
Infection of the intestine by bacteria, viruses, or parasites can cause acute gastroenteritis, damaging the intestinal mucosa and reducing digestive and absorptive function. Food residues undergo abnormal fermentation in the intestine, producing large amounts of decay substances, which may lead to abnormal stool color and odor. Symptoms such as fever, abdominal pain, nausea, and vomiting may also occur. It is recommended to follow medical advice and use medications such as norfloxacin capsules, amoxicillin capsules, or colloidal bismuth pectin capsules to alleviate symptoms.
5. Gallstones
Gallstones may be caused by bacterial infection, reduced gallbladder contraction function, and other factors. Gallstones can affect the normal excretion of bile, causing the stool to become lighter in color or even grayish-white. However, black and foul-smelling stool may also occur, possibly accompanied by symptoms such as jaundice, right upper quadrant abdominal pain, and fever. It is recommended to follow medical advice and use medications such as ursodeoxycholic acid capsules, anti-inflammatory and bile-promoting tablets, or Dankang capsules to alleviate symptoms.
In daily life, it is recommended to maintain good living habits and a healthy diet, avoiding spicy and irritating foods, which helps maintain gastrointestinal health.
References
[1] Lü Mingyue, Zhang Jiao. How to Identify and Manage Gastrointestinal Bleeding [J]. Health Must-Read, 2024, (26): 31-32.
[2] Cheng Li. Distinguishing Truth from Falsehood—Finding the Real Culprit Behind Black Stool [J]. Family Medicine, 2024, (06): 18-19.
