How Gut Bacteria Make Hydrogen Sulfide — and Why It Matters

Hydrogen sulfide is the gas that gives rotten eggs their smell, and your gut bacteria make it every day. For a long time it was viewed purely as a waste product or a toxin. This widely cited 2012 review pulled the evidence together and showed the picture is more nuanced: H2S is both a potential threat to the gut lining and, in small doses, a useful signaling molecule.

Three ways bacteria make sulfide

The authors describe three separate biological routes that produce H2S in the colon:

• Sulfate reduction by specialist bacteria (mainly Desulfovibrio), which use sulfate — abundant in processed foods, meat and eggs — as fuel.
• Cysteine breakdown, where bacteria dismantle sulfur-containing amino acids from protein. The review notes this route may contribute as much sulfide as sulfate reduction, or more.
• Taurine metabolism by Bilophila wadsworthia, a species that thrives on the bile acids released after high-fat meals.

A key practical takeaway is that what you eat decides which pathway dominates — protein, sulfate-rich processed food, and dietary fat each feed a different sulfide-making route.

Why the balance matters

In small amounts, H2S helps relax blood vessels and protects cells. In excess, it can interfere with how the cells lining the colon use their main fuel. The review highlights that people with ulcerative colitis produce roughly three to four times more fecal H2S than healthy people, and that higher sulfide levels have also been linked to colorectal cancer risk.

“The extent to which it is detrimental or beneficial remains in debate.”

The lesson is not that sulfide is simply “bad,” but that its level — strongly shaped by diet — is a window into the balance of activity in your gut microbiome.