Can I tell which type I have from my symptoms?

No, and this has been tested directly rather than assumed. One study found clinical symptoms were not predictive of subtype, and the main clinical guideline states that no single symptom can be specifically attributed to overgrowth at all. Symptom-based type quizzes are answering a question the evidence says symptoms cannot answer.

Can I have more than one type at once?

Yes. In one hydrogen sulfide registry, 24% were positive for both hydrogen sulfide and another gas. Treating the types as mutually exclusive boxes is convenient rather than accurate, and a report naming one gas has not ruled out the others unless the test measured them.

Why does my report only list two gases?

Because most tests sold measure two. Hydrogen sulfide requires different hardware, and a test without it cannot return a result for it in either direction. The absence of a third row on your report is a fact about the test you bought, not about you.

Which gas did your test actually find?

By BeatSIBO editorial team · Updated August 8, 2026

A positive result names a gas. That name does more work than anything else on the report, and it is where most explanations stop.

The three, side by side

The short answer

Hydrogen and methane have published cutoffs and are measured by most tests sold. Hydrogen sulfide has no published cutoff anywhere and is measured by very few tests. So the three types are not three equivalent boxes: two are defined and detectable, and the third is neither, on the same report.

Hydrogen
Published cutoff:
Rise of 20 ppm or more by 90 minutes
Measured by most tests?:
Yes
What names it:
Bacterial overgrowth
Methane
Published cutoff:
10 ppm or more at any point
Measured by most tests?:
Yes
What names it:
Methanogen overgrowth, a different organism
Hydrogen sulfide
Published cutoff:
None. No consensus body has set one
Measured by most tests?:
No
What names it:
No agreed name or criterion

What each gas has behind it
Gas	Published cutoff	Measured by most tests?	What names it
Hydrogen	Rise of 20 ppm or more by 90 minutes	Yes	Bacterial overgrowth
Methane	10 ppm or more at any point	Yes	Methanogen overgrowth, a different organism
Hydrogen sulfide	None. No consensus body has set one	No	No agreed name or criterion

Two of these rows are a measurement. The third is an absence, and it looks identical to a negative on a report that never tested for it.

Rezaie A et al., American Journal of Gastroenterology 2017 Clinical guideline

The consensus that sets these numbers covers hydrogen and methane and contains no hydrogen sulfide criterion. That is not an oversight anyone has since corrected.

The distinction that matters most

The short answer

Methane is not produced by bacteria. It comes from archaea, a separate domain of life, which is why the methane type is increasingly called intestinal methanogen overgrowth rather than bacterial overgrowth. If your result was methane, the word bacterial in your diagnosis is describing the wrong organism.

That has consequences for everything downstream, and it is covered separately because it is the single most misunderstood point in this area.

What the type does not tell you

Scalese G et al., Journal of Clinical Medicine 2025 Peer-reviewed study

Symptoms were not predictive of subtype in that study, and the main guideline says no single symptom can be specifically attributed to overgrowth. So the popular move of reading your symptoms to guess your type is answering a question the evidence says symptoms cannot answer.

What is not settled here

There is also a live argument that the criteria themselves are not established.

Kashyap P et al., Neurogastroenterology & Motility 2024 Peer-reviewed studyWe have not yet confirmed a direct link to this document, so we are not giving you one. The citation above is enough to find it, and we would rather say this than send you to a journal front page.

That source states plainly that the methane and hydrogen sulfide criteria have never been validated. We are not able to settle that disagreement and we are not going to narrate around it. What follows is that a type is a useful organising fact for a conversation with a clinician, and is not the settled sub-diagnosis the confident version of this page would give you.

Where this leaves you

If your report names a gas, the useful next question is what that specific gas changes, and whether the test that produced it could have seen the others at all. Both are answerable. Which type you have, as a settled fact about your body, is less certain than the number on the page makes it look.

Common questions

Can I tell which type I have from my symptoms?: No, and this has been tested directly rather than assumed. One study found clinical symptoms were not predictive of subtype, and the main clinical guideline states that no single symptom can be specifically attributed to overgrowth at all. Symptom-based type quizzes are answering a question the evidence says symptoms cannot answer.
Can I have more than one type at once?: Yes. In one hydrogen sulfide registry, 24% were positive for both hydrogen sulfide and another gas. Treating the types as mutually exclusive boxes is convenient rather than accurate, and a report naming one gas has not ruled out the others unless the test measured them.
Why does my report only list two gases?: Because most tests sold measure two. Hydrogen sulfide requires different hardware, and a test without it cannot return a result for it in either direction. The absence of a third row on your report is a fact about the test you bought, not about you.