Why Does My Poop Smell So Bad? Causes and Clues

You flushed, opened the window, and the smell is still there. MedlinePlus says stools normally smell unpleasant, and the odor is usually a familiar one. Two things are worth checking: whether this smell is different from your usual, and whether anything else changed with it.

Start with yesterday’s meals

MedlinePlus says foul-smelling stools very often have to do with what you eat. Cleveland Clinic describes foods that can cause smelly gas, in a page about gas rather than stool. It says digestion sometimes produces hydrogen sulfide, which smells like rotten eggs. Its sulfur-heavy foods include broccoli, cabbage, eggs, garlic, onions, meats, and beer and wine, and it also names whey protein powders.

If last night was a big egg and broccoli dinner, or you just started a protein shake, and the stool otherwise looks normal for you, start with the menu. MedlinePlus says a provider may ask whether changing your diet makes the smell better or worse.

Smell plus one other sign

Smell is hard to compare day to day, so pair it with whatever else changed. No single row confirms a cause.

The smell comes with	One possibility	What to do
Nothing else unusual, after a change in what you ate	Food	Note the meal, see if it repeats
Greasy, pale, floating, or hard-to-flush stool, once, after a fatty meal	An occasional fatty stool, which Cleveland Clinic says can follow a fatty meal	Log it, watch for repeats
Greasy stool that keeps coming back, with bloating, gas, or weight loss	Malabsorption; the NIDDK lists loose, greasy, foul-smelling bowel movements among its symptoms	See a clinician
Watery diarrhea after antibiotics, with a strong, oddly sweet smell	C. diff infection; Cleveland Clinic says antibiotics are its most common cause	Tell your provider
Diarrhea, gas, cramps, smelly greasy stool that can float	Giardia; the CDC says symptoms usually start 1 to 2 weeks after swallowing the germs, and untreated water from springs, lakes, or rivers raises the risk	Contact a provider
Black stool, or blood	Bleeding in the stomach or intestine, which MedlinePlus lists as a cause	Contact your provider right away

Separate pages cover greasy stool, floating stool, stool changes after antibiotics, and black stool.

Two made-up logs

Made-up example A. Monday dinner: omelette, roasted cauliflower, a whey shake after the gym. Tuesday: Bristol type 4, brown, “rotten egg, strong.” Wednesday: type 4, brown, usual smell.

Made-up example B. Day 6 of antibiotics. Type 7 three times since breakfast, “very strong, oddly sweet,” some cramping.

In A, the smell came and went after one day’s meals while type and color stayed put. The timing could fit food, though the log alone can’t show the cause. In B, the smell matters least. Cleveland Clinic advises telling your healthcare provider if you develop diarrhea after taking antibiotics.

What to write down

MedlinePlus lists questions a provider may ask, including when the change started, what you’ve eaten, and whether stools are pale, black, or hard to flush. Log the answers as you go:

• Bristol type and color (the Bristol stool chart explains the 1 to 7 scale)
• Whether it floated or needed a second flush
• One smell word, used the same way each time
• Yesterday’s meals, plus any new medicine, antibiotic, or supplement
• Fever, chills, cramps, belly pain, or weight change

When to have it checked

In the US, MedlinePlus says to contact your provider for frequent black or pale stools, blood in the stool, fever, chills, cramping, belly pain, or weight loss. With diarrhea, the NIDDK says to talk with a doctor right away about black, tarry stools or stools with red blood or pus, severe pain in the abdomen or rectum, frequent vomiting, or signs of dehydration, and for adults, diarrhea lasting more than 2 days, a high fever, or six or more loose stools a day. Cleveland Clinic says fatty stool you can’t explain should get medical attention. In the UK, the NHS advises calling 111 now for bloody diarrhoea, diarrhoea lasting more than 7 days, or being sick so often you can’t keep fluids down, and 999 or A&E for a sudden, severe tummy ache. Elsewhere, use your own doctor or local emergency number. This article is general information, not medical advice.

How bellySignal helps

In bellySignal, each bowel movement gets a Bristol type from 1 to 7, a color, and blood or mucus flags, and the notes field can hold your smell word. Triggers such as coffee, alcohol, dairy, or poor sleep go into the same diary, along with water in cups or mL and urine color on a 1 to 8 scale. The Trends tab shows your entries over time, and from Settings you can export a 90-day PDF to bring to an appointment. Get bellySignal on Google Play.

Your diary is stored on your device, and no account is required. Selected health values, including stool type, symptoms and manually entered weight, are also sent to PostHog, which is enabled by default. The analytics switch controls PostHog only. Firebase Analytics receives usage events without those health values and remains active. Privacy policy.