Hydrogen Sulfide SIBO: Symptoms, Testing and Treatment

In short: hydrogen sulfide SIBO, sometimes called intestinal sulfide overproductionIntestinal sulfide overproduction (ISO) Excess hydrogen sulfide made by sulfate-reducing bacteria. It is linked to diarrhea and can only be detected by three-gas breath tests., is an overgrowth of bacteria that turn hydrogen into hydrogen sulfide gas. In studies of people with IBS, higher breath hydrogen sulfide goes with diarrhea and with more sulfide-producing bacteria in the stool and small intestine¹². Most breath tests cannot measure it⁵. Newer three-gas tests can, but there is no agreed cut-off and no clinical trials of treatment yet.

SIBO is usually grouped by the main gas on the breath test: hydrogen, methane, or hydrogen sulfide. Hydrogen sulfide is the least studied of the three. This guide covers what is known, and what is not.

What is hydrogen sulfide SIBO?

Many gut bacteria produce hydrogen when they ferment carbohydrates. Some microbes then use that hydrogen. Methane-producing archaeaArchaea Single-celled microorganisms that are distinct from bacteria. Methane-producing archaea (methanogens) are responsible for intestinal methanogen overgrowth. turn it into methane, which is the basis of methane SIBO. Sulfate-reducing bacteriaSulfate-reducing bacteria Bacteria such as Desulfovibrio that consume hydrogen and sulfur compounds and produce hydrogen sulfide gas., such as Desulfovibrio, turn it into hydrogen sulfide, the gas that smells of rotten eggs¹.

The evidence linking hydrogen sulfide to symptoms comes mainly from three studies:

• In a 2016 study of people with diarrhea-predominant IBS, breath hydrogen sulfide differed between those with and without SIBO and changed after the overgrowth was cleared. The researchers proposed it as a marker for SIBO cases that hydrogen tests miss³.
• In a 2022 study of people with IBS from two clinical trials, higher breath hydrogen sulfide went with diarrhea-predominant IBS and with more hydrogen sulfide-producing bacteria in stool, including Fusobacterium and Desulfovibrio¹.
• In a 2025 study that sampled fluid from the upper small intestine, people with breath hydrogen sulfide of 1.5 ppmParts per million (ppm) The unit breath-test laboratories use to report the concentration of hydrogen, methane and hydrogen sulfide in a breath sample. or more had more sulfide-producing bacteria there, and breath levels rose with the number of these bacteria².

Symptoms

The main symptom linked to hydrogen sulfide is diarrhea¹. Hydrogen sulfide is also one of the main gases that make flatus smell⁶, so sulfur-smelling gas is often reported. Otherwise, the symptoms overlap with other types of SIBO: bloating, abdominal pain and discomfort. Our symptoms guide covers SIBO symptoms in general.

Testing

Most breath analyzers used in clinical practice measure only hydrogen and methane⁵. A three-gas test that also measures hydrogen sulfide is available in some countries. Its maker treats a level of 3 ppm or more at any point as positive⁴, but this cut-off has not been adopted by any clinical guideline.

Some people have a “flat line” on a standard two-gas test, with almost no hydrogen or methane. One proposed explanation is that hydrogen sulfide producers are using up the hydrogen, which only a three-gas test can check. You can compare your own readings with the published thresholds in our breath test interpreter.

Treatment

There are no clinical trials of treatment for hydrogen sulfide SIBO. What is known:

• Bismuth. In a 1998 study of 10 healthy adults, bismuth subsalicylate (the active ingredient in Pepto-Bismol), 524 mg four times a day for 3 to 7 days, reduced hydrogen sulfide release from stool by more than 95%. Bismuth binds hydrogen sulfide⁶.
• Practitioner protocols. SIBO practitioners treat hydrogen sulfide with rifaximin plus either bismuth or high-dose oregano oil. If rifaximinRifaximin An antibiotic that is barely absorbed into the bloodstream, so it acts mainly inside the gut. It is a common prescription treatment for SIBO. cannot be used, bismuth and oregano can be taken together or alone⁷.
• Herbal blends. In a 2024 open-label study of 16 people with SIBO who took two commercial botanical supplements for 10 weeks, 67% of those with hydrogen sulfide SIBO had a negative breath test at the end. The number of people in this subgroup was small⁸.

Long-term use of bismuth subsalicylate is not advised without medical supervision: it contains a salicylate related to aspirin and can turn stool and the tongue black.

Diet

Sulfate-reducing bacteria use sulfur, and diets high in protein, which contains sulfur amino acids, are linked to more hydrogen sulfide production. Fiber appears to reduce it, even on a high-protein diet⁹. However, in a small 2019 crossover study of four healthy volunteers, 10 to 14 days of a high- or low-sulfur amino acid diet did not change the amount of sulfate-reducing bacteria in stool¹⁰. Low-sulfur diets for hydrogen sulfide SIBO have not been tested. Our SIBO diet guide covers the diets that have been studied.

Common questions

Is hydrogen sulfide SIBO a recognized diagnosis?

Not yet in the main guidelines. The 2017 North American consensus and 2020 US guideline define cut-offs only for hydrogen and methane¹¹. The evidence for hydrogen sulfide is growing, but it comes mainly from a few research groups.

Can a stool test diagnose hydrogen sulfide SIBO?

No. Stool tests reflect the colon. Higher breath hydrogen sulfide does go with more sulfide-producing bacteria in stool¹, but there is no validated stool test for this condition. See our guide to stool tests.