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What Causes Foul-Smelling Stools?

Feces normally have an unpleasant smell. Foul-smelling stools have an unusually strong, putrid smell. In many cases, foul-smelling stools occur due to the foods people eat and the bacteria present in their colon. However, foul-smelling stools can also indicate a serious health problem. Diarrhea, bloating, or flatulence may occur with foul-smelling stools. These stools are often soft or runny.

What causes foul-smelling stool?

Changes in diet are a common cause of foul-smelling stool. Additional causes include the following:


Malabsorption is also a common cause of foul-smelling stool. Malabsorption occurs when your body is unable to absorb the proper amount of nutrients from the food you eat. This generally occurs when there’s an infection or disease that prevents your intestines from absorbing nutrients from your food.

Common causes of malabsorption include:

  • celiac disease, which is a reaction to gluten that damages the lining of the small intestine and prevents proper absorption of nutrients
  • inflammatory bowel disease (IBD), such as Crohn’s disease or ulcerative colitis
  • carbohydrate intolerance, which is an inability to process sugars and starches completely
  • dairy protein intolerance
  • food allergies

If you have IBD, eating certain foods will cause your intestines to become inflamed. People with IBD often complain of foul-smelling diarrhea or constipation. People with IBD also have flatulence after eating certain foods. This flatulence may have a foul smell.


Infections that affect the intestines may also cause foul-smelling stools. Gastroenteritis, an inflammation of the stomach and intestines, can occur after eating food contaminated with:

  • bacteria, such as Escherichia coli or Salmonella
  • viruses
  • parasites

Soon after developing the infection, you may experience abdominal cramps and then have foul-smelling, runny stools.

Medications and supplements

Certain medications may cause gastrointestinal discomfort and diarrhea. Taking some over-the-counter multivitamins may also cause foul-smelling stools if you’re allergic to the supplements’ ingredients. After a course of antibiotics, you may have foul-smelling stools until your normal bacterial flora is restored.

Foul-smelling diarrhea can be a side effect of taking more than the recommended daily allowance of a multivitamin or any single vitamin or mineral. Diarrhea associated with a multivitamin or medication overdose is the sign of a medical emergency. Getting too much of any of these vitamins can have life-threatening side effects:

  • vitamin A
  • vitamin D
  • vitamin E
  • vitamin K

Other conditions

Other conditions that can cause foul-smelling stools include chronic pancreatitis, cystic fibrosis, and short bowel syndrome.

Symptoms of foul-smelling stool

Symptoms that may occur with foul-smelling stools include:

  • runny stool, or diarrhea
  • soft stool
  • frequent bowel movements
  • abdominal pain
  • nausea
  • vomiting
  • flatulence
  • abdominal bloating

Foul-smelling stools may be the sign of a serious medical condition. See your doctor immediately if you develop any of the following symptoms:

  • blood in your stool
  • black stool
  • pale stool
  • a fever
  • abdominal pain
  • unintentional weight loss
  • chills

How is foul-smelling stool diagnosed?

During your appointment, your doctor will ask questions about your stools, including their consistency and when you first noticed the foul odor. If the consistency of your stools has recently changed, your doctor will want to know when the change occurred. Tell your doctor about any recent changes you’ve made to your diet.

Your doctor may ask for a stool sample to check for bacterial, viral, or parasitic infections. They may also ask to take a blood sample for testing.

Long-term outlook

Your long-term outlook depends on what caused the foul-smelling stool. Most conditions that cause this symptom are treatable. However, diseases such as Crohn’s may require lifelong changes to your diet or medications to control bowel movements and pain.


Make dietary changes

Making dietary changes may help prevent foul-smelling stools. For example, you should avoid drinking raw, or unpasteurized, milk. If you have a disease that affects the way you absorb food or the way your body reacts to eating certain foods, your doctor can devise a diet plan that’s right for you. Following this diet plan can help reduce symptoms such as abdominal pain, abdominal bloating, and foul-smelling stools.

Handle food properly

Avoid bacterial infections from food by handling your food correctly. Cook raw foods such as the following thoroughly before eating:

  • beef
  • poultry
  • pork
  • eggs

Cooking thoroughly means checking your food’s internal temperature with a thermometer before eating. Consult your local health department for the minimum internal temperature each type of food must reach before you eat it.

Don’t prepare meat and vegetables on the same chopping board. Preparing them on the same board can spread Salmonella or other bacteria. You should also wash your hands thoroughly after handling raw meats or using the restroom. 

Content licensed from:

Written by: April Kahn
Medically reviewed on: Apr 14, 2016: University of Illinois-Chicago, College of Medicine

This feature is for informational purposes only and should not be used to replace the care and information received from your health care provider. Please consult a health care professional with any health concerns you may have.
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