Study Reveals Microbes in Your Gut and Mouth May Track Psychopathic Traits

Researchers found that higher levels of certain gut bacteria were tied to higher scores on a self-report psychopathy scale. The authors said this is the first study to examine the gut oral microbiome link to psychopathy traits. But they described the results as preliminary and correlational. They did not show that the microbes cause psychopathic behavior.

Scientists already think the microbiome can influence mood and behavior. Researchers also already link some brain changes with psychopathy. Yet brain differences alone do not explain the full picture. The authors said existing models remain incomplete. They argued the microbiota–brain axis could add another piece to that puzzle.

Earlier studies connect gut microbes with anxiety, depression, and some neurodevelopmental traits. Some work also links oral microbes with neuropsychiatric outcomes. In the psychopathy field, studies often focus on brain structure, empathy, impulse control, and antisocial behavior. The authors said this study extends that work by asking whether gut and oral microbes also track with subclinical psychopathic personality traits.

Costa and colleagues recruited 200 healthy adults in Portugal. Each participant completed the Self-Report Psychopathy Scale Short Form, or SRP-SF. The team also used extra measures of empathy and anxiety. Participants then gave blood, saliva, and stool samples. Researchers ran 16S rRNA gene sequencing on fecal and oral samples to profile bacteria. They also ran targeted and untargeted metabolomics on plasma and fecal samples. For one analysis, they used K-means clustering to group participants by microbiome profiles. Then they compared psychopathy scores and metabolite levels across those clusters.

Overall alpha and beta diversity did not look different between clusters. But beta diversity did correlate with psychopathy scores when the team compared individuals against one another. Higher levels of gut Allisonella, Prevotella, and Cloacibacillus evryensis linked with higher psychopathy scores. Higher levels of oral Treponema vincentii linked with lower psychopathy scores. The authors said these taxa overlapped with subdimensions like callousness, manipulation, impulsivity, and antisociality.

Fecal glucose and taurine levels differed between clusters. Both metabolites also showed positive associations with psychopathy scores. The authors said these metabolites could help explain microbiota–brain interactions. But they did not test those mechanisms directly in this study.

The researchers said the data provide novel evidence linking gut and oral microbiota to subclinical psychopathic traits. They called for more work on biological pathways and biomarker potential. The team framed the results as a new line of inquiry, not as proof of causation.

The study is cross-sectional, so it cannot show cause or direction. The sample was small, at 200 participants. All participants were healthy volunteers, so the results may not generalize to clinical psychopathy. Participants self-reported their traits, which can introduce bias. The microbiome profiles were correlational, and the authors noted they need replication in larger, longitudinal samples. The paper itself was posted as an early-release version and had not completed final publication processing when this summary was written.

This work does not say microbes cause psychopathy. It does not claim a diagnostic test exists, nor does it say the results apply to people with diagnosed antisocial or psychopathic disorders. Finally, it does not replace neurocognitive models of psychopathy.

Reference:

Costa CF, Radford-Smith D, Figueiredo A, et al. Gut and oral microbiota composition is associated with psychopathic personality: a cross-sectional study. Translational Psychiatry (2026). DOI: 10.1038/s41398-026-04052-z.