Most Likely Causes (Ranked)
Eggs, cruciferous vegetables (broccoli, cauliflower, Brussels sprouts), garlic, onions, and red meat are high in sulfur compounds. Gut bacteria break these down into hydrogen sulfide — the rotten egg smell. High-protein diets intensify this.
Antibiotics, illness, travel, or major dietary changes alter your gut microbiome. When beneficial bacteria are reduced, odor-producing bacteria can overgrow, producing more volatile sulfur compounds and short-chain fatty acids.
When you can't digest certain foods (lactose, gluten, fructose), they ferment in the colon instead of being absorbed. This fermentation produces excess gas and foul-smelling compounds.
Infections like C. difficile, Salmonella, E. coli, or parasites like Giardia produce distinctly foul stool — often described as worse than anything you've smelled before. Usually accompanied by diarrhea.
When your body can't absorb fats properly (due to celiac disease, pancreatic insufficiency, or bile duct issues), undigested fat passes into stool — creating pale, greasy, floating, extremely foul-smelling stool called steatorrhea.
Crohn's disease and ulcerative colitis cause chronic inflammation that changes stool composition. Blood, mucus, and inflammatory byproducts create a distinctive, very unpleasant odor.
How to Fix It
Adjust Your Diet
$0Addresses the most common cause.
- 1Reduce sulfur-heavy foods: eggs, red meat, broccoli, cauliflower, garlic, onions.
- 2Increase fiber gradually — it feeds beneficial bacteria and improves stool consistency.
- 3Stay hydrated — concentrated stool smells worse.
- 4Take a probiotic to support healthy gut bacteria, especially after antibiotics.
Identify Food Intolerances
$0-200If specific foods consistently cause problems.
- 1Try an elimination diet: remove suspected trigger (dairy, gluten, or high-FODMAP foods) for 2-3 weeks, then reintroduce.
- 2Keep a food diary linking meals to stool changes.
- 3Lactose intolerance can be confirmed with a hydrogen breath test ($50-200).
- 4Celiac disease requires blood test (tTG-IgA) followed by endoscopy if positive.
See a Doctor
$50-300When diet changes don't help or other symptoms are present.
- 1Stool sample test identifies infections, parasites, and fat malabsorption.
- 2Blood work checks for celiac disease, inflammation markers, and pancreatic function.
- 3Colonoscopy may be recommended for persistent symptoms with blood or mucus.
- 4Most causes are highly treatable once properly diagnosed.
When to Call a Professional
Black, tarry stool — may indicate upper GI bleeding. See a doctor promptly.
Blood or mucus in stool — could indicate infection, IBD, or other conditions needing evaluation.
Pale, greasy, floating stool — sign of fat malabsorption. Needs medical workup.
Persistent foul smell with weight loss — could indicate malabsorption or serious GI condition.
Fever with foul diarrhea — likely infection. See a doctor, especially after travel or antibiotics.
How to Prevent It
Eat a balanced, fiber-rich diet — supports healthy gut bacteria.
Stay hydrated — dilutes waste products.
Take probiotics after antibiotics — restores beneficial gut flora.
Chew food thoroughly — aids digestion and nutrient absorption.
Limit processed foods — artificial sweeteners and additives can upset gut balance.
What Normal Poop Should Smell Like
All stool has an odor — that's normal. The smell comes from bacteria breaking down food in your colon, producing compounds like skatole, indole, and hydrogen sulfide. A mild, familiar unpleasantness is healthy.
The concern is when the smell changes dramatically from YOUR normal baseline, especially if it's accompanied by changes in color, consistency, or frequency. A temporary change after a spicy meal is nothing to worry about. A persistent change over weeks warrants attention.
Frequently Asked Questions
sulfur smell comes from hydrogen sulfide produced when gut bacteria break down sulfur-containing foods (eggs, meat, cruciferous vegetables). Reducing these foods for a few days should improve the smell. If it persists, consider testing for bacterial overgrowth.
Yes. Stress affects gut motility and the microbiome balance, which can change stool composition and odor. The gut-brain connection is well-established — chronic stress can alter digestion enough to change how your stool smells.
Stool that's been in the colon overnight has had more time for bacterial fermentation, producing more volatile compounds. This is normal. Morning bowel movements are often the most odorous simply because of transit time.
See a doctor if: smell persists more than 2 weeks despite dietary changes, stool is bloody/black/pale/greasy, you have unexplained weight loss, or you have persistent diarrhea or abdominal pain. These can indicate conditions that need treatment.