Short answer
Stool smells because gut bacteria break down food and produce sulfur-containing gases and other compounds. Garlic, eggs, red meat, cruciferous vegetables, dairy and constipation can all make it stronger. A sudden, very foul smell that lasts, or comes with greasy stool, blood, diarrhea or weight loss, can point to an infection or a problem absorbing food.
Why does stool smell?
Stool smells because bacteria in your colon ferment what you did not digest. They release compounds such as sulfur gases, indole and skatole, which give stool its smell. The mix depends on what you eat and how long stool spends in the gut.
What makes stool smell worse?
Stool often smells stronger after foods such as garlic, eggs, red meat and cruciferous vegetables, with constipation, and with food intolerances.
- Diet. Garlic, onions, eggs, red meat, cabbage, broccoli, cauliflower and beans.
- Constipation. Stool that stays in the colon longer ferments longer and smells stronger.
- Food intolerance. Lactose or fructose that you cannot digest is fermented by bacteria and can cause smelly gas and stool.
- Medicines and supplements. Antibiotics, and some supplements.
When is smelly stool a sign of a problem?
A very foul stool smell can point to a problem when it lasts, or comes with greasy stool, diarrhea, blood, black stool or weight loss.
- Fat not absorbed (steatorrhea). Celiac disease, pancreas problems and bile problems cause pale, greasy, very foul-smelling stool that floats. See floating, greasy or oily stool.
- Gut infections. Giardia and other infections can cause foul-smelling, often yellow, diarrhea. C. difficile infection after antibiotics is linked with a strong odor and watery diarrhea.
- Inflammatory bowel disease. Crohn's disease and ulcerative colitis can cause foul-smelling diarrhea, sometimes with blood and mucus.
- Bleeding in the upper gut. Black, sticky stool that smells unusually foul can be melena. See black stool.
- Small intestine bacterial overgrowth and other conditions that change how food is digested.
Is smelly baby poop normal?
Breastfed babies' stool often smells mild. Formula-fed babies' stool is often stronger. A sudden strong, foul smell with watery stool, fever or fewer wet diapers should be checked by a pediatrician. See baby poop color.
When should you see a doctor about stool smell?
See a doctor if a very foul stool smell lasts more than a couple of weeks, or comes with greasy stool, diarrhea or weight loss.
Usually harmless
- Strong smell after certain foods, or with constipation
- It settles when your diet or bowels return to normal
Call a doctor
- A very foul smell that lasts more than a couple of weeks
- Foul-smelling, greasy or floating stool
- Smelly diarrhea with weight loss, or after antibiotics
Get care now
- Black, sticky, foul-smelling stool, especially with dizziness
- Foul, bloody diarrhea with fever or severe pain
Warning signs to know
These are signs that published medical guidance says need prompt or urgent care. The list is not complete, and ticking boxes cannot tell you whether you are ill. If you are worried, contact a clinician whatever you tick.
Questions people ask
Why does my poop smell so bad all of a sudden?
Often a food such as garlic, eggs or cruciferous vegetables, constipation, or a short stomach bug. If it lasts more than a couple of weeks, or comes with other changes, see a doctor.
What does foul-smelling diarrhea mean?
It can be an infection such as giardia or a bacterial gut infection, and sometimes C. difficile after antibiotics. See a doctor if it lasts more than two days or you have blood, fever or dehydration.
Is smelly stool a sign of a serious problem?
Not usually on its own. Smell matters more when combined with greasy or pale stool, blood, diarrhea or weight loss.
Can I do anything about stool odor?
Some people notice certain foods make it worse. A persistent, unusual odor should be checked by a doctor rather than masked.
Sources
Important. This page is general information only. It is not medical advice and is not a substitute for advice, diagnosis or treatment from a qualified healthcare professional. StoolColor is not written or reviewed by a doctor, and using this site does not create a doctor-patient relationship. Always ask a doctor or other qualified clinician about any symptom or medical question, and never ignore or delay professional advice because of something you read here.
If you think you may have a medical emergency, call 911 or your local emergency number right away. Information may be incomplete or out of date. Brand names are trademarks of their owners. StoolColor is not affiliated with those owners, or with the organizations whose publications it cites. See our medical disclaimer and terms of use.