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Originally published August 25, 2025
Last updated August 25, 2025
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If you鈥檙e worried about a significant change in the smell of your stool, you may feel too embarrassed to discuss the change with your health care provider. There are instances, however, when seeing a doctor is a good idea.
While food and drinks can temporarily cause changes in your stool, if the changes in your stool persist for days or even weeks, it may warrant concern.
Changes in stool odor, caliber and/or color could indicate a more serious development like cancer, says Sharon Shiraga, MD, an upper-gastrointestinal surgeon with 喵咪社区 who specializes in gastrointestinal conditions. She explains when you should consult a doctor.
Most foul-smelling stool has non-cancerous causes. These can include eating a lot of highly processed foods or eating foods you don鈥檛 normally eat. They can also include conditions like pancreatic insufficiency (when the pancreas doesn鈥檛 produce enough digestive enzymes, causing poor digestion and malabsorption of nutrients) or bacterial infections.
The key to detecting problematic stool odor changes lies in distinguishing between temporary variations and potentially significant alterations.
Temporary changes in stool odor caused by dietary factors are usually not a concern. 鈥淭hat adventurous meal you ate where you saw some stool changes afterward? That is normal,鈥 Dr. Shiraga says.
Stool changes only become concerning if they continue over time despite returning to your normal diet. Although it happens infrequently, foul-smelling dark stool can occasionally indicate bleeding in the gastrointestinal tract caused by the development of a gastrointestinal cancer like colon cancer or stomach cancer.
This cancer-related bleeding produces a distinctive odor: a 鈥渞otten blood鈥 smell that鈥檚 distinctly metallic and appears alongside inky, dark, black stool that continues for days or weeks. 鈥淲hen your stool has blood in it, it becomes darker and smells bad,鈥 Dr. Shiraga says.
She points out that gastrointestinal cancers have varying prevalence rates. Colon cancer represents the third most common cancer overall, stomach cancer affects 3% of the U.S. population and esophageal cancer affects 4.3%. Another type, small bowel cancer, is very rare but highly aggressive when it occurs.
鈥淐ancer-related symptoms are persistent,鈥 Dr. Shiraga emphasizes. 鈥淭hey continue for days or weeks regardless of your diet. If you have bleeding from cancer, it won鈥檛 improve just because you ate tacos today or Thai food tomorrow.鈥
It鈥檚 important to stay alert about any changes in your stool. Understand what your normal stool patterns are so that you recognize any significant deviations. Dr. Shiraga recommends paying attention to the size, color and consistency of your stool.
If you notice any of the following signs, you should consult a doctor:
鈥淚f you notice any of these changes persistently, you need to talk to your health care provider as soon as possible,鈥 Dr. Shiraga advises. Consider recording daily notes about your observations to share with your doctor.
Doctors will evaluate your stool characteristics. They will also consider your personal and family medical history, any associated health symptoms and your overall health status.
They may recommend testing, such as a blood test to detect any hidden blood in your stool or stool tests that can identify bacterial infections. In some cases, an endoscopic exam is recommended.
Most foul-smelling stools have simple explanations like dietary factors or digestive conditions. However, don鈥檛 let embarrassment prevent you from discussing persistent symptoms with your health care provider.
鈥淏e your own advocate,鈥 Dr. Shiraga says. 鈥淒on鈥檛 be shy about having an open discussion with your primary care doctor. Remember that medical professionals have seen it all, so there is no need to feel embarrassed.鈥
Importantly, stay vigilant about monitoring yourself for any changes. 鈥淧ay attention to what鈥檚 normal for you,鈥 Dr. Shiraga says. Keep any eye out for stool odor changes that last for days or weeks.
And maintain perspective, she says. While cancer can occasionally cause stool odor changes, this occurs less frequently than many people fear. Most diagnostic evaluations reveal treatable causes.
Follow recommended colorectal cancer screening protocols. By understanding what to monitor and when to seek care, you can confidently evaluate stool changes and take appropriate action when needed, knowing that most concerns have simple explanations and effective treatments.
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