Hydrogen Sulfide SIBO: Symptoms, Causes, Testing, Diet and Treatment

Hydrogen sulfide SIBO,  also spelt hydrogen sulphide SIBO in the UK,  is one of the newest areas of SIBO research.

Hydrogen sulfide SIBO happens when certain bacteria in the gut make too much of a gas called hydrogen sulfide.

This gas can cause digestive problems such as diarrhoea or loose stools, bloating, tummy pain and lots of win. Some people may also notice that their wind smells like rotten eggs, because hydrogen sulfide is the gas that causes this smell.

Researchers are now sometimes calling this problem intestinal sulfide overproduction (ISO).

Traditional SIBO breath tests usually measure two gases: hydrogen and methane. Newer breath tests can also measure hydrogen sulfide (H₂S), which may help identify people who are producing too much of this gas in their gut.

What is hydrogen sulfide SIBO?

Hydrogen is mainly made when gut bacteria break down carbohydrates. Methane is made by different microorganisms that use hydrogen. Hydrogen sulfide is made in another way, when certain gut microorganisms use sulfur-containing substances.

It is important to know that hydrogen sulfide SIBO is not simply caused by eating too many foods that contain sulfur. How much hydrogen sulfide is produced depends on several things, including which microorganisms are living in the gut, how much hydrogen and sulfur are available, and what conditions are like inside the intestine.

What are the symptoms of hydrogen sulfide SIBO?

Hydrogen sulfide SIBO is most often linked with diarrhoea and loose stools.

Some patients may also experience:

• frequent bowel movements
• a sudden need to go to the toilet
• tummy pain or cramps
• bloating or a swollen tummy
• lots of gas
• wind that sometimes smells like rotten eggs

Research currently shows the strongest link between higher hydrogen sulfide levels and diarrhoea, loose stools, urgency and abdominal pain.

What Causes Hydrogen Sulfide SIBO?

Why Do Too Many Hydrogen-Sulfide-Producing Bacteria Build Up?

Normally, the small intestine has several ways of stopping bacteria from building up. Stomach acid, bile and regular intestinal movement all help keep bacterial numbers under control.

If these protective mechanisms are disrupted, bacteria can remain in the small intestine for longer and start to multiply.

This can happen because of a number of factors including:

• slow movement through the small intestine
• problems with the migrating motor complex, the natural “cleaning wave” between meals
• previous food poisoning or gut infections
• abdominal surgery or structural changes in the intestine
• reduced stomach acid
• changes in bile and digestive secretions
• certain medications or medical conditions that slow digestion

If hydrogen-sulfide-producing bacteria are among the organisms that build up, they can produce larger amounts of hydrogen sulfide gas.

So the problem is not usually that a person has suddenly “caught” hydrogen-sulfide bacteria. These organisms can normally live in the gut. The issue is that conditions in the small intestine may allow too many of them, or too much of their activity, to develop.

Hydrogen sulfide can be produced by sulfate-reducing bacteria, but many other intestinal bacteria can also generate H₂S from sulfur-containing amino acids such as cysteine.

Hydrogen also plays an important role. When bacteria ferment carbohydrates they produce hydrogen, which can then be used by other microorganisms to make methane or hydrogen sulfide. This is why hydrogen, methane and hydrogen sulfide are all interconnected within the gut microbiome.

The most likely explanation is therefore a combination of microbial imbalance, increased H₂S-producing activity and changes in the intestinal environment, rather than one single cause.

How Is Hydrogen Sulfide SIBO Tested?

Most traditional SIBO breath tests measure two gases: hydrogen and methane.

These gases are produced by microorganisms in the gut after a person drinks a test solution, usually containing glucose or lactulose. Breath samples are then collected over the next few hours to see how much gas is being produced.

Hydrogen sulfide is more difficult because most standard SIBO breath tests do not measure it.

A newer breath test called trio-smart measures all three gases: hydrogen, methane and hydrogen sulfide.

This can make it useful when hydrogen sulfide overproduction is suspected. At the time of writing, however, trio-smart is available in the United States and is not available in the UK.

This means someone in the UK can have a normal hydrogen and methane breath test but could still potentially have increased hydrogen sulfide production that has not been measured.

Research supports the idea that hydrogen sulfide production can be relevant in SIBO. Studies looking directly at the bacteria in the small intestine have found increased microbial pathways involved in both hydrogen and hydrogen sulfide production, particularly in people with symptoms such as diarrhoea, abdominal pain and bloating.

What If Your SIBO Test Is Negative?

A negative standard SIBO breath test does not necessarily explain why someone is continuing to experience symptoms.

If hydrogen and methane are normal but symptoms include loose stools, diarrhoea, urgency, abdominal pain, bloating or possibly rotten-egg-smelling gas, hydrogen sulfide overproduction may be one possibility to consider.

However, these symptoms are not unique to hydrogen sulfide SIBO and in some cases can be linked to a parasitic infection.

How Do You Treat Hydrogen Sulfide SIBO?

There is currently no single treatment that has been proven to cure hydrogen sulfide SIBO specifically. Research into hydrogen sulfide and intestinal sulfide overproduction is still quite new, so treatment is usually based on what we already know about SIBO, the person’s symptoms and the possible reasons why too much hydrogen sulfide is being produced.

Treatment may include several different approaches.

Antibiotics

Rifaximin is one of the most commonly used antibiotics for SIBO. It works mainly inside the intestine and is only absorbed into the bloodstream in very small amounts.

Research supports rifaximin for SIBO in general, but most studies have looked at hydrogen-producing SIBO rather than hydrogen sulfide SIBO specifically. Recent reviews continue to identify rifaximin as the most extensively studied antibiotic for SIBO.

This means that although rifaximin may sometimes be considered when hydrogen sulfide SIBO is suspected, we do not yet have enough research to say exactly how effective it is for this particular type.

Hydrogen Sulfide SIBO Natural Treatment

Some patients prefer to try a more natural approach to hydrogen sulfide SIBO and clinically we have had great success in using herbs.

Commonly used herbs include oregano and berberine-containing preparations, although the exact choice depends on the individual’s symptoms, medical history and other medications or supplements.

It is very important to work with an experienced practitioner as these herbs are very strong and may cause side-effects.

These herbs contain natural compounds that can affect the growth and activity of certain microorganisms.

Oregano

Oregano is one of the most commonly used herbal antimicrobials in SIBO protocols.

Oregano contains compounds such as carvacrol and thymol, which have antimicrobial activity.

Published SIBO research has generally used oregano as part of a combination formula, rather than testing oregano alone. For example, a well-known 2014 study used herbal combinations containing oregano and berberine for four weeks and found that 46% of those taking the herbal protocol had a negative follow-up breath test, compared with 34% of those taking rifaximin. The difference was not statistically significant, and this study was not specific to hydrogen sulfide SIBO.

In practitioner protocols, dry or emulsified oregano preparations are sometimes used at approximately:

50–250 mg, two to three times daily.

Some published combination protocols have provided around 240–480 mg of oregano-containing product per day, depending on the formulation.

The exact dose cannot be compared directly between products because an oregano essential-oil preparation may be much more concentrated than powdered oregano leaf.

For this reason, the manufacturer’s formulation and carvacrol content need to be considered rather than looking only at the number of milligrams.

Berberine

Berberine is a plant compound found naturally in herbs such as Berberis, goldenseal and Oregon grape.

It has antimicrobial effects and may also influence the composition of the intestinal microbiome.

In clinical practice, berberine is commonly used at around:

100–500 mg, two to three times daily.

Some SIBO studies have used berberine-containing formulas rather than isolated berberine, so there is currently no established dose that can be said to specifically eradicate hydrogen sulfide SIBO.

Berberine can also interact with medications and may cause nausea, abdominal discomfort or diarrhoea in some people, so it is not suitable for everyone.

Oregano and Berberine Together

A common functional-medicine approach is to combine oregano with berberine rather than relying on one herb alone.

A typical programme might provide approximately:

Oregano: 50–250 mg, two to three times daily

and

Berberine: 100–400 mg, twice daily

for around four weeks, with doses sometimes increased gradually depending on tolerance.

However, this should followed under guidance of a practioner as herbs are very strong and may cause side-effects,

Published studies have generally used branded multi-herb formulas rather than these two ingredients alone.

What Have Published Herbal SIBO Studies Used?

One of the best-known studies compared rifaximin with two different herbal combinations.

Participants taking herbal treatment received either:

Dysbiocide + FC-Cidal — two capsules of each, twice daily

or

Candibactin-AR + Candibactin-BR — two capsules of each, twice daily

for four weeks.

These formulas contained several herbs, including oregano- and berberine-containing ingredients. Approximately 46% of patients taking the herbal preparations had a negative breath test afterwards.

It is therefore impossible to say whether oregano, berberine or another ingredient was responsible for the effect.

Bismuth

Bismuth is another substance that has attracted interest because it can react with and bind hydrogen sulfide inside the gut.

This means it may help reduce the amount of free hydrogen sulfide present and may therefore help some symptoms.

However, bismuth should not be thought of as a proven cure for hydrogen sulfide SIBO. We still need good-quality clinical trials showing whether it can successfully correct intestinal sulfide overproduction over the longer term.

Diet for Hydrogen sulfide

A low-fermentable diet is therefore best thought of as a temporary tool to help control symptoms, rather than a permanent way of eating.

Another part of a natural treatment programme may involve temporarily reducing highly fermentable foods.

Bacteria use certain carbohydrates as fuel. When these carbohydrates are fermented, gases are produced.

Reducing fermentation for a short period may therefore help improve symptoms such as:

• bloating
• abdominal pain
• excessive gas
• diarrhoea
• loose stools
• bowel urgency

A low-FODMAP or lower-fermentable diet may sometimes be used for this purpose.

However, the aim is not usually to follow a very restrictive diet permanently. Foods should normally be gradually reintroduced once symptoms have improved.

This is important because eating a wide variety of foods helps support a healthy and diverse gut microbiome.Food can influence how much fermentation takes place inside the gut.

For this reason, some people with SIBO feel better when they temporarily reduce foods that are very easily fermented by gut bacteria. This may involve a lower-fermentable or modified low-FODMAP diet for a short period.

The aim is not to starve the bacteria permanently. Instead, reducing fermentation for a short time may help control symptoms such as bloating, gas, diarrhoea and abdominal pain while the underlying problem is being treated.

Research supports dietary approaches as a possible part of SIBO management, although the evidence is much less developed than it is for antibiotic treatment.

Do you need to follow a low-sulfur diet?

Because hydrogen sulfide contains sulfur, it is easy to assume that someone with hydrogen sulfide SIBO should simply stop eating sulfur-rich foods.

It is not that straightforward.

Foods such as eggs, meat and many vegetables naturally contain sulfur, but sulfur is also an important nutrient that the body needs.

Hydrogen sulfide production depends on much more than how much sulfur a person eats. It is also affected by which microorganisms are living in the gut, what they are feeding on, how much hydrogen is available and the conditions inside the intestine.

For this reason, there is currently not enough evidence to recommend a strict long-term low-sulfur diet for everyone with suspected hydrogen sulfide SIBO.

Some people may find that temporarily reducing particular foods improves their symptoms, but unnecessarily restricting large groups of nutritious foods can make the diet difficult to follow and may reduce dietary variety.

Support healthy gut motility

Improving the movement of food and bacteria through the small intestine can also be important.

Between meals, the small intestine has a natural cleaning process called the migrating motor complex, or MMC.

The MMC helps sweep leftover food and microorganisms through the small intestine towards the large intestine.

If this process is not working properly, bacteria may remain in the small intestine for longer and have more opportunity to multiply.

Problems with intestinal motility are recognised as an important factor in SIBO, which is why supporting normal gut movement can form an important part of preventing recurrence.

This may involve looking at meal spacing, bowel regularity, physical activity and underlying conditions or medications that may slow digestion.

Can Probiotics Help Hydrogen Sulfide SIBO?

Possibly, but we do not yet have enough research to recommend one particular probiotic specifically for hydrogen sulfide SIBO.

Probiotics are live microorganisms that may help support the balance of bacteria in the gut.

However, different probiotic strains can behave very differently. This means probiotics should not be thought of as one single treatment.

Some people with SIBO find probiotics helpful, while others notice that they increase symptoms such as bloating, gas or discomfort.

For this reason, probiotics are usually best considered individually, depending on a person’s symptoms, test results and overall digestive health, rather than assuming that everybody with SIBO needs to take one.

Saccharomyces boulardii may be a useful to consider in some people with SIBO, particularly where diarrhoea is present. Unlike most probiotics, it is a beneficial yeast rather than a bacterium. Clinical studies suggest it may help reduce bacterial overgrowth and digestive symptoms, although it has not yet been specifically proven to treat hydrogen sulfide SIBO.

One caution: S. boulardii is generally well tolerated, but it should be avoided or medically supervised in severely immunocompromised people or those with central venous catheters, because very rare bloodstream infections have been reported.

What cause Hydrogen Sulfide SIBO?

Perhaps the most important part of natural treatment is understanding why the overgrowth developed.

Possible contributing factors can include:

• slow intestinal motility
• previous food poisoning or gastrointestinal infection
• certain medications
• previous abdominal surgery
• structural changes in the digestive tract
• other digestive or medical conditions

If these factors are not addressed, symptoms may return even after successful antimicrobial treatment.Improving movement through the gut

Another important part of treatment is making sure food and bacteria move properly through the small intestine.

Between meals, the small intestine has a natural cleaning system called the migrating motor complex (MMC).

You can think of the MMC as a small cleaning wave that sweeps leftover food and bacteria through the small intestine and towards the large intestine.

If this movement becomes too slow or does not work properly, bacteria can remain in the small intestine for longer and may have more opportunity to multiply.

This is one reason why improving intestinal motility may form part of a SIBO treatment plan. Recent research also continues to identify impaired intestinal motility as an important factor in SIBO, and some studies have investigated combining SIBO treatment with medicines that improve gut movement.

Treatment needs to look at the bigger picture

The aim of treatment is therefore not simply to “kill hydrogen sulfide.”

Hydrogen sulfide itself is a gas. The real aim is to understand why certain gut microorganisms are producing too much of it and to improve the conditions that allowed this imbalance to develop.

Treatment may therefore involve a combination of:

reducing excessive microbial activity, controlling fermentation, improving gut movement, reducing symptoms and addressing any underlying causes.

Because research into hydrogen sulfide SIBO is still developing, there is no single treatment plan that is right for everyone.

Treatment is best personalised according to a person’s symptoms, breath-test results, bowel habits, medical history and overall digestive health.

How Is Hydrogen Sulfide SIBO Different From Other Types of SIBO?

The main difference between hydrogen sulfide SIBO and other forms of intestinal overgrowth is which gas is being produced and which microorganisms are involved.

With hydrogen SIBO, bacteria in the small intestine ferment carbohydrates and produce hydrogen gas. This is often linked with bloating, gas, abdominal discomfort and sometimes diarrhoea or loose stools.

With methane overgrowth, microorganisms called methanogens use hydrogen and convert it into methane. Methane is more strongly linked with constipation and slower movement through the gut. Because methanogens are not bacteria and may live in both the small and large intestine, the preferred term is intestinal methanogen overgrowth, or IMO, rather than methane SIBO.

With hydrogen sulfide overproduction, certain microorganisms use hydrogen and sulfur-containing compounds to produce hydrogen sulfide gas. This pattern is more often associated with diarrhoea, bowel urgency, loose stools and abdominal pain.

Researchers are increasingly using the term intestinal sulfide overproduction, or ISO, rather than simply hydrogen sulfide SIBO.

These different patterns can also interact with each other.

Hydrogen is often used as a fuel by other microorganisms. Methanogens can use hydrogen to produce methane, while sulfide-producing microorganisms can use hydrogen to help produce hydrogen sulfide.

This means the gases are not always completely separate, and some people may have a mixed pattern.

A simple way to think about it is:

Hydrogen SIBO involves bacteria producing excess hydrogen.

Methane overgrowth involves methanogens turning hydrogen into methane.

Hydrogen sulfide overproduction involves microorganisms using hydrogen and sulfur compounds to make hydrogen sulfide.

The symptoms can overlap, so bowel habit alone cannot confirm which type is present. Breath testing, where available, can help identify the gas pattern involved.

Need Help With Suspected Hydrogen Sulfide SIBO?

If you are experiencing persistent diarrhoea, bloating, abdominal discomfort, excessive gas or suspect you may have hydrogen sulfide SIBO, consider booking a SIBO consultation. We offer consultations at our sister clinic the IBS and Gut Disorder Clinic

We can help you understand your symptoms, decide whether testing may be useful, interpret existing SIBO results and explore possible underlying causes.

Book a Consultation With a SIBO Specialist

If you would like individual support, you can book a consultation with a SIBO specialist at our sister clinic IBS and Gut Disorder Clinic

Frequently Asked Questions

What kills hydrogen sulfide in SIBO?

There is currently no single treatment proven specifically to eradicate hydrogen sulfide SIBO. Treatment may include antibiotics or herbal antimicrobials together with strategies to improve intestinal motility and address underlying causes.

What are the main symptoms of hydrogen sulfide SIBO?

The symptoms most strongly associated with hydrogen sulfide are diarrhoea, loose stools, bowel urgency and abdominal pain. Bloating and excessive gas can also occur.

What foods should I avoid with hydrogen sulfide SIBO?

There is not enough evidence to recommend a strict low-sulphur diet for everyone. Individual food triggers can be identified and temporarily reduced, but unnecessarily restrictive diets should generally be avoided.

Why am I producing so much hydrogen sulfide?

Excess H₂S production may result from changes in the gut microbiome, increased activity of hydrogen-sulfide-producing microorganisms, available hydrogen and sulphur-containing compounds, and changes in the intestinal environment.

Can I have hydrogen sulfide SIBO if my normal SIBO test was negative?

Yes, potentially. Traditional SIBO tests measure hydrogen and methane but may not measure hydrogen sulfide. A negative two-gas test therefore does not necessarily rule out hydrogen sulfide overproduction.

Does hydrogen sulfide SIBO always cause rotten egg gas?

No.

Hydrogen sulfide is responsible for the characteristic smell of rotten eggs, so sulphurous-smelling flatulence can occur when H₂S production is increased.

But the absence of rotten-egg-smelling gas does not rule it out.

The amount of gas produced, where it is produced, how much is absorbed through the intestinal wall and how efficiently the body metabolises it will all influence whether somebody notices a distinctive smell.

Equally, experiencing occasional rotten-egg-smelling gas does not prove that somebody has hydrogen sulfide SIBO.

It can be a clue, but it is not a diagnostic test.

Can hydrogen sulfide SIBO cause a flat-line breath test?

Possibly, but a flat-line SIBO breath test does not prove that somebody has hydrogen sulfide SIBO.

Before hydrogen sulfide could be measured directly, clinicians sometimes suspected H₂S production when a breath test showed persistently very low hydrogen and methane levels.

The theory is biologically plausible.

Hydrogen may be produced by fermenting bacteria but then rapidly consumed by other microorganisms to produce hydrogen sulfide, leaving relatively little hydrogen to appear in the breath.

Earlier consensus literature acknowledged this proposed explanation, but also noted that the significance of the flat-line pattern was uncertain.

More recent consensus work continues to regard a flat-line pattern as potentially suggestive of intestinal sulfide overproduction rather than diagnostic of it.

So if your hydrogen and methane SIBO test is negative or unusually flat, hydrogen sulfide is one possible explanation — but it is not the only explanation.

Can a normal SIBO test miss hydrogen sulfide SIBO?

Yes, potentially.

A conventional SIBO breath test that measures only hydrogen and methane cannot directly detect hydrogen sulfide.

This is one reason somebody could theoretically have symptoms and hydrogen sulfide overproduction despite not meeting the conventional criteria for hydrogen-positive SIBO or methane-positive IMO.

This does not mean that every negative SIBO test represents hydrogen sulfide SIBO.

Negative results can occur for many reasons and should always be considered alongside symptoms, preparation, the test substrate used and the wider clinical history.

Is hydrogen sulfide SIBO the same as IBS-D?

No.

IBS-D is a clinical syndrome characterised by IBS symptoms with predominantly diarrhoeal stools.

Hydrogen sulfide overproduction may be present in a proportion of people with IBS-D, but not everybody with IBS-D has hydrogen sulfide SIBO or ISO.

Is hydrogen sulfide SIBO the same as sulphur intolerance?

No. Food reactions can have numerous causes, and many foods described as “high sulphur” contain other components capable of triggering gastrointestinal symptoms. Reacting to sulphur-containing foods does not establish a diagnosis of hydrogen sulfide SIBO.

Medical Disclaimer: The information in this article is for general educational purposes only and is not intended to diagnose, treat or cure any medical condition. Hydrogen sulfide SIBO is still an evolving area of research, and the treatments discussed, including herbal antimicrobials, dietary changes and supplements, may not be suitable for everyone. Always seek advice from a suitably qualified healthcare professional before starting treatment, particularly if you are pregnant, breastfeeding, taking medication or have an existing medical condition.

References

1. Villanueva-Millan MJ, Leite G, Mathur R, et al. Hydrogen Sulfide and Methane on Breath Test Correlate with Human Small Intestinal Hydrogen Sulfide Producers and Methanogens. 2025. PMID: 40569514.

This study provided important evidence linking breath hydrogen sulfide with hydrogen-sulfide-producing organisms detected directly within the human small intestine.

2. de Freitas Germano J, Leite G, Villanueva-Millan MJ, et al. Transcriptomics profiles in intestinal sulfide overproduction, small intestinal bacterial overgrowth, and intestinal methanogen overgrowth. mSystems. 2026;11(7). PMID: 42370695. DOI: 10.1128/msystems.00458-26.

This 2026 study identified distinct small-bowel transcriptomic patterns associated with intestinal sulfide overproduction, SIBO and IMO.

3. Villanueva-Millan MJ, Leite G, Wang J, et al. Methanogens and Hydrogen Sulfide Producing Bacteria Guide Distinct Gut Microbe Profiles and Irritable Bowel Syndrome Subtypes. American Journal of Gastroenterology. 2022;117(12):2055–2066. PMID: 36114762. DOI: 10.14309/ajg.0000000000001997.

4. Suarez FL, Furne JK, Springfield J, Levitt MD. Bismuth subsalicylate markedly decreases hydrogen sulfide release in the human colon. Gastroenterology. 1998;114(5):923–929. PMID: 9558280. DOI: 10.1016/S0016-5085(98)70311-7.

The study found a greater than 95% reduction in faecal H₂S release after short-term bismuth subsalicylate administration in ten healthy volunteers. It was not a hydrogen sulfide SIBO treatment trial.

5. Rezaie A, Chang BW, de Freitas Germano J, et al. Effect, Tolerability, and Safety of Exclusive Palatable Elemental Diet in Patients With Intestinal Microbial Overgrowth. Clinical Gastroenterology and Hepatology. 2025;23(12):2306–2317.e7. PMID: 40189034. DOI: 10.1016/j.cgh.2025.03.002.

Author – Victoria Tyler BSc Hons MBANT

Victoria Tyler owns and runs two busy clinics : Nutrition and Vitality and the IBS and Gut Disorder Clinic.

Nutrition and Vitality, along with the IBS and Gut Disorder Clinic, were founded with the goal of helping patients alleviate IBS symptoms by uncovering and addressing the root causes of their digestive issues.

As a Registered Nutritional Therapist, Victoria holds a BSc (Hons) in Nutritional Therapy and has trained with the Institute of Functional Medicine. She is also accredited by BANT and CNHC.

Before transitioning into health, Victoria earned a degree in Economics and an MBA, working with corporations including Canon and Vodafone. However, her own health challenges led her to pursue a career in Nutritional Therapy.

With a passion for learning, Victoria is committed to staying at the forefront of Functional Medicine. She helps patients manage IBS and other digestive disorders, including SIBO, Candida, and IBD, by identifying and addressing their root causes.

Victoria strongly believes that every symptom has an underlying cause, and there is always a solution to every health condition. To learn more, or to see patient reviews, visit Victoria’s profile on Google.

DISCLAIMER: The information provided in this article is intended for general informational purposes only and should not be construed as medical advice, diagnosis, or treatment. The products and methods mentioned are not a substitute for professional medical advice from a trained healthcare specialist. Always seek the guidance of your doctor or other qualified health professional with any questions you may have regarding your health or a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website. Use of the information and products discussed is at your own risk.