December 5, 2025, 4:06 pm | Read time: 5 minutes
A dog is more than just a loyal friend—it could also boost mental health. A recent study from Japan provides initial evidence that living with dogs can influence the oral microbiome in teens, thereby improving social skills. But what exactly happens in the body? And can love for dogs really lead to better relationships?
Microbiome Can Influence Brain Function
Puberty is a key phase for social and emotional development, as the brain is particularly receptive to environmental influences during this time. Dogs are considered beneficial for mental balance—they provide comfort, reduce stress, and strengthen social bonds. However, many questions remain, such as: How exactly does dog ownership affect well-being?
Previous studies show that dogs can change not only the psyche but also the microbiome of their owners. Close contact through petting or licking allows for the transfer of microbes between dog and human. It is also known that the microbiome influences brain function—particularly through the so-called gut-brain axis, where bacteria can control social behavior. But do dogs also affect the oral microbiome of adolescents? And if so, how does this impact their psychological and social behavior?
Does Dog Ownership Improve Social Behavior?
To answer this question, Japanese researchers led by Eiji Miyauchi and Takefumi Kikusui from Azabu University examined how living with dogs affects the mental well-being of adolescents. The new study was published in the journal “iScience.”
The researchers analyzed not only psychological data from 343 adolescents but also transplanted their oral microbiota into germ-free mice to observe possible effects on social behavior. The results show a connection between dog ownership, altered microbial composition, and improved social behavior—both in humans and mice.1
Saliva Samples Were Transplanted into Mice
Three hundred forty-three adolescents, aged 13 to 14 at the time of data collection, were studied. Of these, 96 owned a dog, while 247 did not. A year later, the adolescents’ mental state was assessed using the Child Behavior Checklist (CBCL). This involves questionnaires that capture behavioral issues, emotional problems, somatic complaints, and social competencies of school-aged children and adolescents from the parents’ perspective.2
To clarify possible causal relationships, saliva samples from all adolescents (with and without dogs) were analyzed to determine the oral microbiome. The researchers then transplanted these into germ-free mice. Subsequently, the social behaviors of the animals were examined.
Microbiota from Dog Owners Promote Social Approach Behavior
Adolescents with dogs showed significantly fewer social and emotional problems than their peers without dogs. Social issues, withdrawal, aggressive, and delinquent behaviors were particularly reduced. These effects persisted even after adjusting for demographic factors.
Microbiome analyses revealed that certain bacterial genera—particularly Streptococcus—were more common in the saliva of dog owners. The overall diversity of microbes remained the same, but specific microbes differed in frequency.
In the mouse study, animals treated with microbiota from dog owners exhibited stronger social approach behavior toward their peers. Notably, Streptococcus species (specifically certain ASVs—amplicon sequence variants) correlated with both the social behavior of the mice and the psychological parameters of the adolescents. Some of these bacteria were associated with positive sociality, while others were linked to more negative behavior, indicating functional differences within this genus.
Bacteria from Dogs Influence Microbiome and Behavior in Adolescents
The results suggest a possible biological mechanism by which dog ownership in youth can improve social behavior: through changes in the oral microbiome, which communicates with the brain via complex signaling pathways. Particularly noteworthy is that some microbes had similar effects in mice as in the adolescent donors, indicating a shared effect through the microbiota.
The study provides initial evidence that microbial changes due to pet ownership could be significant not only in the digestive tract but also in the mouth. Identifying certain Streptococcus species as potentially beneficial for social behavior is a promising starting point for future research.
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Study Based Only on Adolescents from Urban Tokyo
Despite the exciting results, the study has several limitations. For humans, only saliva samples were examined, while stool samples were analyzed in mice, limiting comparability. Additionally, the 16S rRNA sequencing used in the study to differentiate between bacterial strains has limited explanatory power. More precise results would require so-called metagenomic data.
Another point: It is unclear whether the differences in the microbiome are caused by the dog itself or by secondary effects (such as stress reduction). Furthermore, the study is based on adolescents from urban Tokyo, which may limit the generalizability of the results. Lastly, it remains open whether the observed effects persist long-term—longitudinal studies would be needed for this.
Conclusion:
Dog ownership during adolescence appears to be associated with improved social behavior and a changed oral microbiome. This study is the first to suggest that certain bacteria—particularly Streptococcus ASV—could play a role in mental health. Although causality has not yet been definitively established, the results show how closely mental well-being, pets, and microbiology could be intertwined. For pet owners and researchers alike, this opens up new perspectives on the interplay between animals and humans.