What Causes Foul-Smelling Stool?

By Andrew Yocum, MD
Medically reviewed checkmarkMedically reviewed
April 6, 2022

Regular stools don’t have a pleasant odor, and there’s a good reason for that—stool is a product of bacteria in the colon breaking down digested food.

And this process of breaking down digested food comes with a not-so-rosy smell.

But most of us can recognize the difference between the way our stool usually smells and when something causes it to smell even worse than usual.

If you’re experiencing particularly foul-smelling stools, you may be wondering what’s behind them.

Changes in diet can cause especially foul-smelling stool, but there are other reasons for your stool to smell differently that may warrant medical attention.

Understanding the possible causes of foul-smelling stool can help you determine whether or not to seek advice from a medical professional.

What Causes Foul-Smelling Stool

There are several possible causes of foul-smelling stool.

Diet

Changes in diet can affect the way your stool smells.

For example, eating more spicy food or higher quantities of meat than you usually do will likely produce stronger smelling stools. Significant changes to your diet while traveling can also change the way your stool smells.

Food Allergies

Eating foods that you’re allergic to or that your body has trouble processing can also produce foul-smelling stools. Specifically, eating foods with lactose if you’re lactose intolerant can result in foul-smelling stools.

Intestinal Infection

Foul-smelling stools may also be a sign of an intestinal viral, bacterial (like E. coli or Salmonella), or parasitic infection.

These infections can occur after eating contaminated food or drinking contaminated water (which can also happen when swimming).

With an intestinal infection, you may have other symptoms, like severe stomach pain or cramps, diarrhea, nausea, or fever. 

Malabsorption

Malabsorption is a condition in which the body has trouble absorbing certain sugars, fats, proteins, or vitamins, which can cause foul-smelling stool.

Additional symptoms of malabsorption include chronic diarrhea, bulky stools, bloating, cramping, gas, and fatty stools. 

Malabsorption can be caused by several diseases, including:

  • Celiac disease
  • Chronic pancreatitis
  • Cystic fibrosis
  • Crohn’s disease
  • HIV or AIDS
  • Chronic liver disease
  • Ulcerative colitis
  • Chronic pancreatitis
  • Tropical sprue
  • Short bowel syndrome
  • Whipple disease
  • Radiation treatment for cancer

Medication

Certain medications may also cause foul-smelling stools.

This can happen if you take a medication or supplement that contains an ingredient you’re allergic to, but it can also happen when you take antibiotics.

While on antibiotics, you may notice temporary foul-smelling stools that last until the natural balance of bacteria in your gut is restored.

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What to Keep an Eye Out For

Changes in stool that are related to changes in your diet are usually temporary—once you return to your normal diet, your stool should return to its normal smell within a few days.

However, if your foul-smelling stool persists for several days regardless of a return to your normal diet, reach out to your healthcare provider for more information.

Additionally, there are some symptoms you should watch out for if you’re experiencing particularly foul-smelling poop:

If you experience any of the above symptoms, reach out to your healthcare provider as soon as possible.

Diagnosis

When speaking with a healthcare professional about the cause of your foul-smelling stool, your provider will likely conduct a physical exam and ask you questions about your medical history.

They will also ask you questions specific to your changes in stool and diet. Questions you can expect to answer include:

  • When did the change in your stool first take place?
  • Are your stools a different color than usual?
  • Are your stools a different consistency than usual or are they difficult to flush?
  • Have there been any recent changes to your diet?
  • Have you traveled recently?
  • Are you experiencing any additional symptoms?
  • Have you ever noticed a change in your stool’s smell in the past?

Depending on your answers, your provider may also ask for a stool sample to check for a bacterial, viral, or parasitic infection. Other tests may also be recommended.

Prevention

There are several things you can do to help prevent an infection or reaction that can cause foul-smelling stool:

  • Stick to a regular diet: Avoiding drastic changes to your diet can help to prevent foul-smelling stools.
  • Avoid foods as recommended by your provider: If diagnosed with lactose intolerance, celiac disease, inflammatory bowel disease, or another condition, your provider may recommend following a specific diet (like avoiding dairy or gluten). Following this recommended diet closely can help to prevent foul-smelling stool and other bothersome symptoms that can impact your quality of life, like abdominal pain, bloating, and more. 
  • Handle food safely: Practicing good food hygiene can help prevent some bacterial infections, like E. coli and Salmonella infections. These practices include washing your hands thoroughly before food preparation, washing all produce before cooking or eating, cooking all meat to the minimum appropriate temperature using a meat thermometer, and using different cutting boards for meat and vegetable preparation.
  • Use medications and supplements safely: Check with your provider before taking any medications or supplements to ensure that they are safe to take and will not cause unwanted side effects, like foul-smelling stool.  
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When to See a Doctor

If you’re experiencing foul-smelling stool that won’t go away, reach out to your provider for help.

It’s also important to seek immediate medical attention if you notice any additional symptoms, including bloody stool, fever, severe abdominal cramping, chills, or abnormally colored stools.

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Frequently Asked Questions

What causes foul-smelling poop?
There are several possible causes of foul-smelling poop, including specific foods, allergies, medication, infections, and some underlying medical conditions. If you’re unsure about the cause of your foul-smelling poop, reach out to a healthcare provider for more information. It’s particularly important to reach out to your provider if you’re experiencing foul-smelling stools that won’t go away or any additional symptoms, like severe stomach pain, blood in stool, or fever.
What is the most common cause of smelly stool?
Generally, foul-smelling stool is caused by diet. Specifically, it can be caused by eating certain foods, like when people with lactose intolerance eat dairy products. In most cases, occasional foul-smelling stool will not require treatment. But if your poop continues to smell bad, it could be a result of an imbalance in your microbiome or, in more severe cases, a disease like inflammatory bowel disease. To confirm the cause of your bad-smelling poop, reach out to your healthcare provider for more information.
How can I stop my poop from smelling?
Although foul-smelling poop cannot always be prevented, there are some things you can do to decrease the risk of developing foul-smelling poop. For starters, be sure to follow any dietary recommendations laid out by your healthcare provider (like avoiding dairy if you’re lactose intolerant or avoiding gluten if you have celiac disease). It’s also important to practice good food safety and hygiene when cooking to help prevent bacterial infections. This includes washing your hands thoroughly before preparing food, washing all produce before eating or cooking, and cooking all meats to the minimum recommended temperature using a meat-specific thermometer.

K Health articles are all written and reviewed by MDs, PhDs, NPs, or PharmDs and are for informational purposes only. This information does not constitute and should not be relied on for professional medical advice. Always talk to your doctor about the risks and benefits of any treatment.

Andrew Yocum, MD

Dr Andrew Yocum is a board certified emergency physician. He graduated Summa Cum Laude from Kent State University with a Bachelor of Science in Molecular Biology before attending Northeast Ohio Medical University where he would earn his Medical Doctorate (MD).

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