Stool smell comes primarily from sulfur-containing gases and other volatile compounds produced when gut bacteria break down food. That means the most effective way to reduce stool odor is to change what you feed those bacteria. Diet is the single biggest lever, but hydration, probiotics, and certain supplements can all make a noticeable difference.
Why Stool Smells in the First Place
Your large intestine is home to trillions of bacteria that ferment whatever your small intestine didn’t fully absorb. This fermentation produces a cocktail of volatile organic compounds: organic acids, alcohols, phenols, and sulfur gases like hydrogen sulfide, the chemical behind that rotten-egg smell. The more sulfur-containing material your bacteria have to work with, the worse things smell.
Certain species of gut bacteria, including Bilophila and Desulfovibrio, specialize in metabolizing sulfur compounds from food. When these bacteria get a steady supply of sulfur-rich ingredients, they ramp up hydrogen sulfide production. Excess hydrogen sulfide doesn’t just smell bad. It’s also been linked to intestinal inflammation.
Cut Back on High-Sulfur Foods
The foods most strongly associated with sulfur production in the gut are animal-based proteins, particularly red meat and processed meats. These are rich in sulfur-containing amino acids that gut bacteria ferment directly into hydrogen sulfide. A dietary pattern high in animal-source foods, fried potatoes, sauces and gravies, refined grains, and alcohol has been identified as especially promoting sulfur metabolism in the gut.
If you’re looking for a straightforward first step, reducing your intake of red and processed meat for a week or two is the most likely dietary change to produce results. Cruciferous vegetables like broccoli, cabbage, and cauliflower also contain sulfur compounds, though they come with fiber and nutrients that generally benefit gut health. If your stool is particularly foul, try cutting back on these temporarily to see if it helps, then reintroduce them gradually.
Drink More Water
Dehydration slows everything down. Research on water restriction found that cutting water intake in half doubled gut transit time, meaning food sat in the intestines twice as long. That extended transit gives bacteria more time to ferment and produce odor compounds. Low water intake also increases the total bacterial count in stool and shifts the composition of gut microbial communities in unfavorable ways.
Constipation and hard stools are both signs that you’re not drinking enough. Adequate water keeps stool moving at a pace that limits excessive fermentation. There’s no magic number, but if your urine is consistently dark yellow, you’re likely underhydrating.
Try a Probiotic
Probiotics can shift the balance of your gut bacteria away from the species that produce the worst-smelling compounds. A clinical trial using a blend of Lactiplantibacillus plantarum and Pediococcus acidilactici strains found that stool odor was significantly reduced within one week of starting the supplement, with improvement continuing over four weeks. Flatulence odor also decreased, though that took the full four weeks to reach significance.
Not every probiotic will have the same effect. Look for multi-strain products that contain Lactobacillus or Bifidobacterium species, as these tend to produce lactic acid rather than sulfur gases during fermentation. Give any probiotic at least two to four weeks before judging results.
Enzyme Supplements for Food Intolerances
If specific foods consistently make your stool smell terrible, you may be partially unable to digest them. Undigested food reaching the colon is a feast for gas-producing bacteria. Up to 75% of the world’s population has some degree of lactose intolerance, and more than 20% of people experience significant intestinal gas from complex carbohydrates in beans and certain vegetables.
Lactase supplements, taken with dairy, break down lactose before it reaches the colon where bacteria would otherwise ferment it. Similarly, alpha-galactosidase supplements break down the non-absorbable fiber in beans and root vegetables before it can ferment. Taking these before meals prevents the problem rather than masking it afterward.
Chlorophyllin and Internal Deodorizers
Chlorophyllin, a water-soluble derivative of the green pigment in plants, has a long history of use as an internal deodorizer. Studies in nursing home settings found that chlorophyllin tablets helped control both body and fecal odors, while also easing constipation and reducing excessive gas. It’s available over the counter, often marketed as “internal deodorant” or sold as liquid chlorophyll drops.
Bismuth-based products (the active ingredient in some pink stomach remedies) can also darken and deodorize stool by binding to sulfur compounds in the gut. These work quickly but aren’t meant for daily long-term use.
Manage the Smell in the Moment
While you’re working on the root causes, a few practical tricks help with bathroom odor. Turn on the exhaust fan before you sit down, not after. Ventilation works best when it’s already moving air. If your bathroom has a window, opening it early dilutes odor compounds as they’re produced. Pre-toilet spray products that create a film on the water’s surface can trap some volatile compounds below the waterline. A box of matches works in a pinch: the sulfur dioxide from a struck match temporarily masks bathroom odors.
When Foul Stool Signals Something Else
A sudden, persistent change in stool odor that doesn’t respond to dietary changes can point to a medical issue. Celiac disease, Crohn’s disease, chronic pancreatitis, and intestinal infections like giardiasis all cause characteristically foul-smelling stool. Giardiasis, a parasitic infection often picked up from contaminated water, produces explosive, watery, foul-smelling stools and can lead to nutrient malabsorption if untreated.
Fat malabsorption is another common culprit. When your body can’t properly digest fats, you’ll notice bulky, pale, oily stools that tend to float and are difficult to flush. The smell is distinctly worse than normal. This can result from pancreatic insufficiency, bile acid problems, or conditions like celiac disease damaging the intestinal lining.
Blood in the stool, whether visible or hidden, also changes the smell in a distinctive metallic or unusually sharp direction. If your stool odor has changed dramatically and stays that way for more than a couple of weeks despite dietary adjustments, or if you notice greasy, floating stools, unexplained weight loss, or persistent diarrhea alongside the smell, those are signs worth investigating with a healthcare provider.