Burps that smell like rotten eggs combined with diarrhea almost always trace back to hydrogen sulfide, a gas produced by certain bacteria in your gut as they break down sulfur-containing compounds from food or from bile. Hydrogen sulfide is the same molecule responsible for the smell of rotten eggs in nature, and when enough of it builds up in your digestive tract, it rises as sulfur burps and can signal that something downstream is also off. The pairing with diarrhea is not coincidental: the same bacterial imbalances and digestive disruptions that generate excess hydrogen sulfide tend to speed up transit through the colon or irritate its lining.
Where the Smell Actually Comes From
Your gut is home to trillions of bacteria, and a subset of them, called sulfate-reducing bacteria, thrive on sulfate compounds found in certain foods and in bile. Their metabolic end product is hydrogen sulfide gas. When these bacteria are present in normal amounts, you produce small quantities of hydrogen sulfide that the colon lining can usually absorb and neutralize. Problems start when the population of sulfate-reducing bacteria grows disproportionately large or when more sulfur-containing material reaches them than usual. The excess gas has nowhere to go but up and out, giving your burps that unmistakable rotten-egg quality.
At high concentrations in the gut, hydrogen sulfide does more than just smell bad. It can damage the intestinal lining and shift the local pH in ways that disrupt the broader microbial community. Research on sulfate-reducing bacteria has shown that elevated hydrogen sulfide is linked to gut inflammation, partly because it is directly toxic to the cells lining the colon.1PubMed Central. Hydrogen sulfide toxicity in the gut environment: Meta-analysis of sulfate-reducing and lactic acid bacteria in inflammatory processes That inflammation can loosen the gut barrier and trigger watery stools, which is why sulfur burps and diarrhea so often travel together.
Common Dietary Triggers
Before assuming something is medically wrong, it helps to look at what you ate in the past day or two. Sulfur-rich foods are the single most common reason for a temporary episode of eggy burps and loose stools. The usual culprits include eggs (especially the yolks), cruciferous vegetables like broccoli, cauliflower, and cabbage, garlic, onions, red meat, and dairy products, particularly aged cheeses. Beer and wine can also contribute because the fermentation process leaves behind sulfite compounds.
High-protein diets deserve special mention. When you eat more protein than your small intestine can fully absorb, the undigested fraction reaches the colon, where bacteria ferment the sulfur-containing amino acids cysteine and methionine into hydrogen sulfide. A big steak dinner followed by sulfur burps the next morning is a textbook example. Artificial sweeteners like sorbitol and sugar alcohols found in “sugar-free” products can compound the problem by drawing water into the intestine and accelerating transit, which means both more gas production and looser stools.
If your symptoms show up only occasionally and line up with a dietary binge, the fix is usually straightforward: scale back the sulfur-heavy foods for a few days and see if things settle. Keeping a rough food diary for a week or two can help you spot patterns you might otherwise miss.
When Gut Bacteria Are Out of Balance
If sulfur burps and diarrhea keep recurring regardless of what you eat, the bacterial mix in your intestine may have shifted in a way that favors hydrogen sulfide producers. This is sometimes called dysbiosis, a catch-all term for a microbial community that has drifted away from its usual healthy composition.
Research on people with diarrhea-predominant irritable bowel syndrome (IBS-D) has found a clear pattern: higher levels of breath hydrogen sulfide that correlate with a larger population of hydrogen sulfide-producing bacteria such as Fusobacterium and Desulfovibrio species, alongside lower overall microbial diversity.2PubMed Central. Methanogens and Hydrogen Sulfide Producing Bacteria Guide Distinct Gut Microbe Profiles and Irritable Bowel Syndrome Subtypes In other words, the gut loses variety and becomes dominated by sulfur-metabolizing organisms, and the result is both more gas and more diarrhea. The same study found that metabolic pathways associated with sulfate reduction were enriched specifically in IBS-D patients, reinforcing the hydrogen sulfide connection to loose stools.
Broader research into functional gut disorders confirms that an altered microbiota can drive several of the mechanisms behind chronic symptoms, including abnormal motility, immune activation in the gut wall, and impaired barrier function.3JGH Open. Gut microbiota dysbiosis in functional gastrointestinal disorders: Underpinning the symptoms and pathophysiology So while sulfur burps are the most noticeable sign, they may be part of a bigger picture of gut imbalance that also explains bloating, cramping, and urgency.
Small Intestinal Bacterial Overgrowth (SIBO)
SIBO is one of the more underdiagnosed reasons for persistent sulfur burps with diarrhea. It happens when bacteria that normally live in the colon migrate upward and colonize the small intestine, where they ferment food earlier than they should. The result is excessive gas production, malabsorption of nutrients, and often diarrhea.
Hydrogen sulfide appears to play a specific role in SIBO. Research has shown that breath hydrogen sulfide levels are distinctly altered in people with diarrhea-predominant IBS who also have SIBO, driven by the activity of sulfate-reducing bacteria that have taken up residence in the small bowel.4Journal of Breath Research. Hydrogen sulphide in exhaled breath: a potential biomarker for small intestinal bacterial overgrowth in IBS The same work found that tracking breath hydrogen sulfide could even follow the progression of SIBO and detect whether treatment had successfully cleared the overgrowth, which is significant because traditional breath tests sometimes miss SIBO entirely.
Symptoms of SIBO overlap heavily with general IBS, which is part of why it gets missed. If you have sulfur burps, diarrhea, bloating that gets worse through the day, and unexplained fatigue or nutrient deficiencies, SIBO is worth asking your doctor about.
Infections That Cause Sulfur Burps and Diarrhea
Acute infections are another common cause, especially when the onset is sudden. Giardia, a parasite spread through contaminated water, is practically famous for producing sulfur burps alongside explosive, foul-smelling diarrhea. The infection disrupts fat absorption in the small intestine, leading to greasy stools and excessive gas. If your symptoms started after travel, camping, or exposure to untreated water, giardiasis should be high on the suspect list. A stool test can usually confirm it, and a course of antibiotics clears it in most cases.
Helicobacter pylori, the bacterium behind most stomach ulcers, can also alter gas dynamics in the gut. Research has demonstrated that H. pylori uses hydrogen gas as a respiratory fuel during colonization of the stomach lining, and its presence distinctly changes breath gas profiles.5Journal of Breath Research. Molecular hydrogen in human breath: a new strategy for selectively diagnosing peptic ulcer disease, non-ulcerous dyspepsia and Helicobacter pylori infection While H. pylori more commonly causes upper abdominal pain, nausea, and acid reflux, it can also contribute to changes in burp composition and, in some people, looser stools.
Viral gastroenteritis, the ordinary stomach bug, can temporarily produce sulfur burps too. The infection damages the intestinal lining and shifts the microbial environment, allowing sulfate-reducing bacteria to flourish temporarily. These episodes usually resolve within a few days with hydration and rest.
Bile Acid Diarrhea
Bile acid diarrhea (sometimes called bile acid malabsorption) is a condition that flies under the radar for many people and doctors alike. Normally, bile acids are released into the small intestine to help digest fats, then reabsorbed near the end of the small bowel. When that reabsorption fails, excess bile acids spill into the colon. Research has shown that in bile acid diarrhea, bile acid production can increase six- to sevenfold beyond normal levels, and those excess acids trigger fluid secretion and high-amplitude contractions in the colon, resulting in urgent, watery diarrhea.6PubMed Central. Bile acid diarrhoea: pathophysiology, diagnosis and management
The connection to sulfur burps is indirect but real. Bile contains sulfur-conjugated compounds, and when excess bile reaches the colon, sulfate-reducing bacteria have more raw material to work with. People with bile acid diarrhea often describe particularly foul-smelling gas and stools. The condition can follow gallbladder removal, Crohn’s disease affecting the terminal ileum, or it can occur on its own with no obvious trigger. A medication called a bile acid sequestrant (cholestyramine is the most common) is the standard treatment and works well for most people.
Medications That Can Trigger These Symptoms
Several medications can produce the sulfur burps-plus-diarrhea combination as a side effect. Antibiotics are the most obvious offender: by wiping out large swaths of your normal gut flora, they can allow sulfate-reducing species to expand unopposed. Metformin, one of the most widely prescribed diabetes drugs, is notorious for causing GI symptoms including diarrhea and foul-smelling gas, especially in the first weeks of treatment.
More recently, GLP-1 receptor agonists like semaglutide and liraglutide (the drugs behind Ozempic and Wegovy) have drawn attention for their gastrointestinal side effects. Nausea, vomiting, diarrhea, and constipation are the most frequently reported problems, typically emerging during the dose-escalation phase.7PubMed. Safety and Tolerability of Glucagon-Like Peptide-1 Receptor Agonists: A State-of-the-Art Narrative Review These drugs slow gastric emptying substantially, which means food sits in the stomach longer and can ferment. If you recently started or increased a GLP-1 medication and noticed sulfur burps with diarrhea, the drug is a strong suspect. The symptoms often improve as your body adjusts to the dose, but mention them to your prescriber if they persist.
Proton pump inhibitors (PPIs) like omeprazole, taken long-term for acid reflux, can also contribute by reducing stomach acid enough that bacteria survive the stomach and colonize the small intestine, potentially setting the stage for SIBO.
What You Can Do at Home
For occasional episodes, a few practical steps can help:
- Cut back on sulfur foods: Temporarily reducing eggs, cruciferous vegetables, garlic, onions, and high-protein meals gives your gut less raw material for hydrogen sulfide production.
- Stay hydrated: Diarrhea depletes fluids and electrolytes quickly. Water with a pinch of salt and sugar, or an oral rehydration solution, helps more than plain water alone.
- Try bismuth subsalicylate: The active ingredient in Pepto-Bismol has been shown to bind hydrogen sulfide and markedly decrease its release in the colon.8PubMed. Bismuth subsalicylate markedly decreases hydrogen sulfide release in the human colon It is one of the few over-the-counter options with direct evidence for reducing sulfur gas. Note that it can temporarily turn your tongue and stools black, which is harmless.
- Consider a probiotic: Lactic acid bacteria, the kind found in many probiotic supplements and fermented foods, have properties that counterbalance sulfate-reducing bacteria and can help reduce gut inflammation.1PubMed Central. Hydrogen sulfide toxicity in the gut environment: Meta-analysis of sulfate-reducing and lactic acid bacteria in inflammatory processes
- Eat slowly and avoid carbonation: Swallowing air adds volume to burps, and carbonated drinks push even more gas upward.
These measures address symptoms rather than root causes. If you find yourself reaching for bismuth subsalicylate more than a couple of times a month, that pattern itself is a reason to get a proper workup.
How Doctors Investigate Persistent Cases
When sulfur burps and diarrhea become chronic or come with additional red flags like weight loss, blood in the stool, or fever, your doctor will likely start with blood work and a stool sample to rule out infections and inflammation. The stool test can detect parasites like Giardia, bacterial pathogens, and markers of inflammatory bowel disease.
Breath testing has become increasingly important in diagnosing conditions associated with excess gut gas. Traditionally, breath tests measured only hydrogen and methane to diagnose SIBO and other fermentation problems. Recently, hydrogen sulfide was added as a third gas, and nationwide data has confirmed its association with diarrhea as a primary symptom.9PubMed Central. Real-world Study of Three-gas Breath Testing Nationwide and the Association With Symptoms The three-gas breath test involves drinking a sugar solution (usually lactulose or glucose) and then breathing into a collection device at intervals over two to three hours. Elevated hydrogen sulfide on this test points toward sulfate-reducing bacterial overgrowth and can help guide treatment, which typically involves targeted antibiotics like rifaximin.
For suspected bile acid diarrhea, the diagnostic pathway is different. A SeHCAT scan (common in the UK and Europe) or a trial of a bile acid sequestrant is often used, since direct testing for bile acid levels is not widely available in every country. If suspected, a positive response to cholestyramine or colesevelam essentially confirms the diagnosis.
Food Intolerances That Mimic the Pattern
Lactose intolerance and fructose malabsorption can both produce a combination of gas, bloating, and diarrhea that people sometimes describe as having a sulfurous quality, though the primary gas in these conditions is hydrogen rather than hydrogen sulfide. The distinction matters because the treatment is different: avoiding the specific sugar you cannot absorb, rather than targeting sulfur-producing bacteria.
Celiac disease is worth mentioning here too. Damage to the small intestinal lining from gluten exposure impairs nutrient absorption broadly, and the malabsorbed material that reaches the colon can feed sulfate-reducing bacteria, producing hydrogen sulfide as a downstream effect. People with undiagnosed celiac disease often report foul-smelling gas and chronic diarrhea for months or years before getting a diagnosis. A blood test for tissue transglutaminase (tTG) antibodies is a reliable first screen.
Why the Two Symptoms Show Up Together
It is worth stepping back to appreciate why rotten-egg burps and diarrhea are so tightly linked rather than occurring independently. Hydrogen sulfide at elevated levels in the gut sets off a cascade. It irritates the mucosal lining, which prompts the colon to secrete more fluid as a protective response. It increases motility, meaning the colon contracts more forcefully and moves contents through faster, leaving less time for water reabsorption. And it shifts the local bacterial ecosystem toward a less diverse, more inflammatory state, which further weakens the gut barrier.2PubMed Central. Methanogens and Hydrogen Sulfide Producing Bacteria Guide Distinct Gut Microbe Profiles and Irritable Bowel Syndrome Subtypes So the gas you are tasting on the way up is the same molecule causing trouble on the way down. One symptom is not a coincidence alongside the other; they share a common driver.
When Sulfur Burps Happen Without Diarrhea, and Vice Versa
Not everyone who gets sulfur burps also gets diarrhea, and the reverse is true as well. Sulfur burps alone, especially after a sulfur-heavy meal, are generally not worrisome. They usually reflect temporary overproduction of hydrogen sulfide in the stomach or upper small intestine that dissipates within a few hours. Gastroparesis, where the stomach empties slowly, can also trap food long enough for sulfur gases to build up and escape upward without affecting the colon at all.
Diarrhea without sulfur burps has an even wider range of causes, from stress and anxiety-driven motility changes to inflammatory bowel disease, infections, and medication side effects. The specific pairing of both symptoms together narrows the field considerably toward causes involving sulfate-reducing bacteria, malabsorption of sulfur-containing compounds, or infections that disrupt the upper and lower GI tract simultaneously.
If you are experiencing both together for the first time and it resolves within a day or two, a dietary trigger or mild stomach bug is the most likely explanation. If the combination recurs regularly, especially if you are losing weight, seeing blood in your stool, or running a fever, those are signs that something beyond diet needs medical attention. A three-gas breath test, stool studies, and sometimes upper endoscopy or colonoscopy can help pin down the cause and get you to a treatment that addresses the root problem rather than just masking the symptoms.