Checking assumptions on SIBO and Hydrogen Sulfide breath test

A reader ping me about Hydrogen Sulfide(H2S) breath tests and Small Intestinal Bacterial Overgrowth.  A light went on for a question that may need to be asked:

  • Is it
    • An overgrowth of H2S producing bacteria, OR
    • An undergrowth of bacteria that uses H2S?

Having excessive H2S in the breath is a known fact. The traditional reason behind it may be speculation. It may also ignore dental health, stress levels, etc and may be recording a different issue.

  • “The tongue coating score had a significant positive correlation with H2S [tongue coating area  and tongue coating thickness ” [2015]
  • “The stressed students group showed increased oral emanations of hydrogen sulfide and dimethyl sulfide,  ” [2017]
  • hydrogen sulphide and methane were decreased in inflammatory bowel disease compared to healthy controls” [2015]

What really surprise me was that there was not dozen of articles on PubMed when I searched for “hydrogen sulfide small intestinal bacterial overgrowth” but just TWO!!!!

  • One article dealt with SIBO in combination with IBS-D. “Here, we show that hydrogen sulphide (H2S) in exhaled breath is distinctly altered for diarrhea-predominant IBS individuals with positive and negative SIBO by the activity of intestinal sulphate-reducing bacteria. ” [2016]
  • “Although higher hydrogen sulphide and SRB levels have been detected in patients with IBD, and to a lesser extent in colorectal cancer, this colonic gas might have beneficial effects.” [2012] see below — it is anti-inflammatory!

 Sulphur and bacteria

  • Metabolic niche of a prominent sulfate-reducing human gut bacterium [2013]. ” increasing the abundance of the H2S-producing Actinobacterium, Collinsella aerofaciens.” and a decrease of E.Coli
  • Lactobacillus brevis, Lactobacillus lindneri and Pediococcus damnosus, and some Gram-negative bacteria such as Pectinatus cerevisiiphilus, Pectinatus frisingensis and Megasphaera cerevisiae..and the production of unfavorable smell such as diacetyl or hydrogen sulfide.”[2003]
  • Study of constancy of hydrogenconsuming flora of human colon [1994].
  • “The amount of H2S produced by periodontopathic bacteria or oral bacteria collected from human subjects decreased after an incubation with rSox enzymes. These results suggest that the combination of rSox enzymes from P. pantotrophus GB17 is useful for the prevention of oral malodor.” [2017]
  • Hydrogen sulfide (H2S) is recognized as a biological mediator with various roles such as neuromodulation, regulation of the vascular tone, cytoprotection, anti-inflammation, oxygen sensing, angiogenesis, and generation of mitochondrial energy. ” [2014]
  • “H2S is produced by enzymes from l-cysteine; cystathionine β-synthase, cystathionine γ-lyase, and 3-mercaptopyruvate sulfurtransferase (3MST) along with cysteine aminotransferase.” [2013]
    • “The production of H2S from D-cysteine is 80 times more efficient than that from L-cysteine in the kidney,” [2014]
  • “Endogenous hydrogen sulfide (H2S) renders bacteria highly resistant to oxidative stress,  but its mechanism remains poorly understood.”
  • Staphylococcus aureus is a commensal human pathogen and a major cause of nosocomial infections. As gaseous signaling molecules, endogenous hydrogen sulfide (H2S) and nitric oxide (NO·) protect S. aureus from antibiotic stress synergistically…thus linking sulfide homeostasis to an adaptive response to antimicrobial reactive nitrogen species.” [2017]
  • “The extensive crosstalk between NO and hydrogen sulfide (H2S) related metabolites may further affect nitrate’s bioactivity.” [2017]


A reader forwarded a link to Measurement of Hydrogen Sulfide during Breath Testing Correlates to Patient Symptoms (2017)  The authors of this published earlier in 2017, “The focus of this research has been to find non-invasive biomarkers from serum, breath gas, and fecal materials. T..To date, these types of biomarkers for IBS have been disappointing.”

This citation deals with IBS and not SIBO — two different conditions (with some possible overlaps) — I am working on a post examining what SIBO is or is not.

Bottom Line

I am an evidence based person and have come to two surprising conclusions:

  • There is no evidence that we can connect high hydrogen sulfide to SIBO in general
  • There is no evidence that reducing hydrogen sulfide is in a person’s interest (yes, it may be an offensive breath to people) — in fact, it may be the body trying to reduce inflammation.

As always, please share any PubMed links (the gold standard for evidence) that may further clarify the evidence.

I know this runs contrary to common alternative medicine beliefs – “show me the evidence”!