Burps that smell like feces are caused by sulfur-rich gases, specifically hydrogen sulfide, methanethiol, and dimethyl sulfide, traveling up from your digestive tract. These are the same compounds responsible for the smell of stool and flatulence. Most of the time, the cause is something manageable like bacterial imbalance or a high-protein diet, but in rare cases it can signal a serious blockage in your intestines.
The Gases Behind the Smell
Your gut bacteria break down food and produce gases as a byproduct. When those bacteria ferment poorly digested protein or sulfur-containing compounds, they generate hydrogen sulfide (the classic rotten-egg gas), methanethiol, and dimethyl sulfide. In normal digestion, most of these gases pass downward as flatulence. But when something disrupts that process, whether it’s slow motility, bacterial overgrowth, or a physical blockage, those gases can travel upward and exit through your mouth as foul-smelling burps.
Bacterial Overgrowth in the Small Intestine
One of the most common causes of persistent sulfur burps is a condition called SIBO, where bacteria that normally live in your large intestine colonize the small intestine instead. These misplaced bacteria ferment food too early in the digestive process, producing excess hydrogen, methane, and hydrogen sulfide. The hydrogen sulfide-dominant form is particularly associated with sulfur burps, sewer-smelling stool, bloating that gets worse as the day goes on, and unpredictable bowel patterns that alternate between diarrhea and constipation.
SIBO often develops when something slows the normal movement of food through your gut. That could be prior abdominal surgery, certain medications (especially opioids), diabetes affecting gut nerves, or conditions like irritable bowel syndrome. Treatment typically starts with a course of antibiotics to reduce the overgrown bacteria. The improvement is often significant, but the bacteria can return once antibiotics stop, so some people need repeated or long-term treatment. Doctors also try to address whatever caused the overgrowth in the first place, whether that means adjusting medications or repairing structural problems surgically.
Severe Constipation and Slow Gut Motility
When stool sits in your colon for too long, it continues to ferment and produce gases that have nowhere to go but up. Chronic constipation, especially the kind caused by opioid medications or neurological conditions, can slow your gut to the point where fecal matter backs up significantly. In extreme cases, this stagnation leads to fecal breath, a distinct poop-like odor that comes through with every exhale and burp.
The mechanism is straightforward: as the colon distends with impacted stool, volatile sulfur compounds seep backward through the digestive tract. In one documented case, a patient with opioid-induced constipation developed such severe fecal impaction that material actually regurgitated upward, producing an unmistakable fecal odor on his breath. That’s an extreme scenario, but milder versions of the same process happen whenever constipation causes prolonged fermentation in the colon.
Intestinal Obstruction
A full or partial blockage in the intestines is the most serious possible cause. When the intestine is physically blocked, whether by scar tissue from prior surgery, a hernia, a tumor, or twisted bowel, nothing can pass through. Contents back up, ferment, and the resulting gases rise through the stomach and out as foul burps. In some cases, people with obstructions vomit material that smells fecal.
This is the cause you need to rule out quickly. The warning signs that separate an obstruction from less dangerous causes are clear: severe abdominal pain that comes in waves, vomiting (especially if it smells fecal), a completely bloated and rigid abdomen, and the inability to pass gas or have a bowel movement at all. If you have fecal-smelling burps combined with these symptoms, that combination needs emergency evaluation. An obstruction on its own is not common in younger adults, but among people 65 and older, the global incidence runs above 640 cases per 100,000 people per year.
High-Sulfur Foods and Protein-Heavy Diets
Sometimes the explanation is simply what you ate. Your gut bacteria produce more hydrogen sulfide when they have more sulfur-containing material to work with. The two main dietary sources are sulfur-rich amino acids found in protein (cysteine, methionine) and inorganic sulfur compounds used as food additives (sulfites, sulfates, carrageenan).
In Western diets, protein is the bigger contributor. Fecal sulfide concentrations rise proportionally with the amount of meat you eat, because more undigested protein reaches the lower gut where bacteria ferment it. Foods especially high in sulfur-containing amino acids include red meat, eggs, dairy, cruciferous vegetables like broccoli and cabbage, garlic, and onions. Beer and wine also contain sulfites that feed sulfide-producing bacteria.
If your sulfur burps come and go and seem tied to meals, reducing your intake of high-protein and high-sulfur foods for a few days is a reasonable first experiment. Researchers have developed low-sulfur dietary approaches (like the 4-SURE diet) that specifically target hydrogen sulfide production by avoiding sulfur-rich proteins and sulfite-containing additives. You don’t need to follow a formal protocol. Just cutting back on red meat, eggs, and processed foods with sulfite preservatives for a week or two can tell you whether diet is the main driver.
Other Contributing Factors
Gastroparesis, a condition where the stomach empties abnormally slowly, can trap food long enough for it to ferment and produce foul-smelling gas. This is most common in people with diabetes or after certain surgeries. The burps often come with nausea, early fullness, and bloating after small meals.
Gastroesophageal reflux (GERD) doesn’t typically cause fecal-smelling burps on its own, but it creates a more open pathway between the stomach and mouth that makes it easier for odorous gases from lower in the digestive tract to travel upward. If you already have reflux, any of the other causes on this list can produce more noticeable odor.
Infections with certain bacteria, particularly those that produce hydrogen sulfide as a metabolic byproduct, can also be responsible. A stomach infection with specific strains of gut bacteria can temporarily shift your microbiome toward heavy sulfide production, causing sulfur burps that resolve once the infection clears.
Figuring Out the Cause
A single episode of foul-smelling burps after a heavy protein meal is almost certainly dietary and not worth worrying about. Recurring sulfur burps over days or weeks, especially with bloating, changed bowel habits, or abdominal discomfort, point toward SIBO or another motility issue worth investigating. Your doctor can test for SIBO with a breath test that measures hydrogen and methane levels after you drink a sugar solution.
The pattern matters more than any single episode. Sulfur burps that worsen throughout the day suggest bacterial overgrowth fermenting food as it moves through your gut. Burps that are worst in the morning or after long gaps between meals may point to gastroparesis or severe reflux. And burps accompanied by inability to pass gas, escalating pain, and vomiting represent a potential emergency that shouldn’t wait for a scheduled appointment.