Why does my poop smell so bad?

Reviewed by Yoshinori Abe, MD

Internal Medicine

Foul-smelling poop is often caused by what you eat, how your body digests food, or an infection in your gut. Common triggers include high-fat or high-sulfur foods, food intolerances (like lactose or gluten), malabsorption conditions such as celiac disease or pancreatitis, and infections from bacteria, viruses, or parasites. Certain medications and supplements can also change stool odor. While occasional smelly stools are usually harmless, persistent foul odor—especially with diarrhea, bloating, weight loss, or blood—may signal an underlying condition that needs attention.

Because the causes range from simple dietary triggers to more serious digestive disorders, it's important to understand what your specific symptoms could mean before deciding on next steps. A free, instant, online symptom check can help you narrow down potential causes based on your unique health profile and guide you toward the right care—whether that's a diet adjustment, a pharmacy visit, or seeing a doctor.

Reviewed for medical accuracy: 07/15/2026

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Explanation

Inside your digestive tract, many tiny bacteria called gut microbes work to break down your food. When your diet is low in fiber or high in processed foods and meats, these bacteria might produce extra smelly chemicals. Drinking alcohol can also cause foul-smelling poop. Digestive issues, such as irritable bowel syndrome, can change the way your gut works, making the smell of your poop different and stronger. And, certain medications, like antibiotics, can disrupt your normal gut bacteria balance, leading to changes in stool odor. Infections, such as Clostridioides difficile and Giardia, can also cause poop to smell particularly bad because these pathogens release toxins and disrupt the normal balance of gut bacteria. If you experience other associated symptoms like severe pain or if the smell is persistent, you can use this free symptom checker to help identify what might be causing your symptoms and determine if you should talk with a doctor.

(References)

National Research Council (US) Committee on Diet and Health. Diet and Health: Implications for Reducing Chronic Disease Risk. Washington (DC): National Academies Press (US); 1989. 10, Dietary Fiber.
Nelkowska DD. Treating irritable bowel syndrome through an interdisciplinary approach. Ann Gastroenterol. 2020 Jan-Feb;33(1):1-8. doi: 10.20524/aog.2019.0441. Epub 2019 Nov 29. PMID: 31892791; PMCID: PMC6928481.
Dalal RS, Allegretti JR. Diagnosis and management of Clostridioides difficile infection in patients with inflammatory bowel disease. Curr Opin Gastroenterol. 2021 Jul 1;37(4):336-343. doi: 10.1097/MOG.0000000000000739. PMID: 33654015; PMCID: PMC8169557.

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