Poop that smells like sulfur, often described as a rotten-egg smell, is usually caused by hydrogen sulfide gas produced when bacteria in your gut break down proteins. This is a normal part of digestion, and in most cases, the smell traces back to something you ate rather than a medical problem.
How Bacteria Create That Sulfur Smell
Your gastrointestinal tract is home to billions of bacteria, and some of them specialize in breaking down proteins from the food you eat. When these bacteria digest animal or vegetable proteins, they produce hydrogen sulfide, the same colorless gas responsible for the smell of rotten eggs. The more sulfur-containing protein that reaches your lower intestine, the more hydrogen sulfide your gut bacteria generate, and the worse your stool smells.
This process is completely normal. Everyone’s stool contains some hydrogen sulfide. What varies is the amount, which depends on what you’ve been eating, the specific mix of bacteria living in your gut, and how quickly food moves through your system. A sudden shift toward sulfur-heavy foods can temporarily ramp up gas production and make the smell noticeably worse.
Foods That Make It Worse
The most common reason for sulfur-smelling stool is diet. Sulfur enters your gut through two main routes: amino acids in protein-rich foods and sulfur compounds in certain vegetables.
- High-protein animal foods: Turkey, beef, eggs, fish, and chicken are all rich in methionine, an essential amino acid that contains sulfur. A steak-heavy dinner or a few hard-boiled eggs can noticeably change stool odor the next day.
- Cruciferous vegetables: Broccoli, cauliflower, cabbage, kale, arugula, and radishes contain sulfur in the form of glucosinolates. These are healthy compounds, but they give gut bacteria plenty of raw material to work with.
- Allium vegetables: Garlic, onions, leeks, scallions, and shallots are packed with sulfur compounds that contribute to both breath and stool odor.
- Dried fruits, beer, and wine: These contain sulfites or other sulfur-based preservatives that can increase hydrogen sulfide production in the colon.
If you recently loaded up on any combination of these foods, that’s likely your answer. The smell typically resolves within a day or two as your diet shifts.
Medications and Supplements
Certain medications can also change stool odor. Antibiotics disrupt the normal balance of gut bacteria, which can lead to diarrhea and foul-smelling stools as different bacterial populations take over. This usually resolves after you finish the course of treatment.
Multivitamins and fat-soluble vitamin supplements (vitamins A, D, E, and K) have also been linked to changes in stool smell and gastrointestinal discomfort. If the timing of your sulfur-smelling stool lines up with starting a new supplement, that connection is worth noting.
Malabsorption and Digestive Conditions
When your body can’t properly absorb nutrients, undigested food lingers in the intestine longer than it should, giving bacteria extra time and material to ferment. This produces more gas, including hydrogen sulfide, and often results in particularly foul-smelling stool.
Celiac disease is one well-known cause. People with classical celiac disease often develop pale, fatty, foul-smelling stools along with diarrhea and weight loss. The damage to the small intestine prevents proper fat and nutrient absorption, leaving more for bacteria to break down. Lactose intolerance works through a similar mechanism: undigested lactose ferments in the colon, producing gas and odor.
Conditions affecting the pancreas or liver can also impair digestion. If your stool is consistently light-colored or pasty in addition to smelling strongly of sulfur, that pattern can point to problems with bile or digestive enzyme production.
Infections That Change Stool Odor
Gut infections, particularly parasitic ones, can produce distinctly foul-smelling stool. Giardia, a parasite often picked up from contaminated water during travel or camping, causes explosive, watery, greasy stools with a notoriously bad smell. Other symptoms include bloating, nausea, gas, fatigue, and loss of appetite.
Bacterial infections can produce a similar picture. If your sulfur-smelling stool came on suddenly alongside diarrhea, especially after recent travel or after taking antibiotics, an infection is a real possibility.
When the Smell Signals Something More
On its own, foul-smelling stool is rarely a sign of cancer or another serious disease. Doctors look for additional factors before suspecting something more concerning. The questions that matter most are whether you also have diarrhea, unexplained weight loss, blood in your stool, or a recent change in bowel habits.
Stool color provides useful clues. Bright red or black, tarry stool is suspicious for bleeding somewhere in the digestive tract. Light or pasty stool can indicate a liver or pancreas problem. Normal brown stool that simply smells worse than usual is far less worrying.
The timeline matters too. A few days of sulfur-smelling stool after a big holiday meal is nothing to worry about. Symptoms that persist for more than a couple of weeks deserve medical attention, especially if they come with other changes like weight loss, persistent diarrhea, or visible changes in stool color or consistency.
How to Reduce the Smell
If you’ve ruled out infections and medical conditions, dietary adjustments are the most effective way to cut down on hydrogen sulfide production. Reducing your intake of the biggest sulfur sources, like red meat, eggs, cruciferous vegetables, garlic, and onions, for a week or two can help you identify which foods are the main contributors. You don’t need to eliminate these foods permanently. Just eating them in smaller amounts or less frequently can make a noticeable difference.
Bismuth subsalicylate, the active ingredient in Pepto-Bismol, has been shown to dramatically reduce hydrogen sulfide levels in the gut. It works by binding to sulfide compounds before they become gas. It’s available over the counter in both liquid and tablet form. Green tea extract has also shown some ability to lower hydrogen sulfide production, making it a gentler option worth trying.
Paying attention to patterns helps. If the smell consistently follows certain meals, your gut bacteria are telling you exactly which foods are responsible. Keeping a simple food diary for a week can make these connections obvious in a way that guessing never does.