There is a compelling biological reason why dogs have earned the title “man’s best friend.” Research now suggests that living with dogs doesn’t just affect us emotionally—it may also influence our biology in ways that support social and mental well‑being.
A study conducted by researchers at Azabu University in Japan, published in iScience in December 2025, found that adolescents who lived with dogs showed distinct differences in their microbial composition, particularly in their oral microbiomes, compared to those without pets.
Specifically, teenagers who grew up with dogs exhibited fewer social problems, lower levels of aggression and social withdrawal, and higher overall mental well-being than their peers who did not live with dogs.
Microbiome differences—not just companionship
To explore whether these benefits were linked to biological mechanisms rather than emotional factors alone, researchers analyzed oral microbiome samples. The team treated laboratory mice with microbiota from dog‑owning adolescents and discovered those mice exhibited increased social interaction, spending more time sniffing cage mates and showing a greater tendency to approach and assist a trapped cage-mate—a standard behaviour test used to test prosocial behaviour in mice.
How microbes may influence the brain
These findings fit within the framework of the gut-brain axis, a bidirectional system through which the gut microbiota is known to influence behaviour via immune, hormonal, and neural pathways.
Importantly, the Azabu University study does not claim that dog microbes directly “rewrite” the human brain. Instead, it suggests that microbiome changes associated with dog ownership may help shape social behaviour and emotional regulation during adolescence, a critical period of psychological and neurodevelopment sensitivity.
Why dogs may be especially influential
Dogs are highly effective microbial carriers. They spend time outdoors, roll in the dirt, interact with soil and plants, and bring a wide range of environmental microbes on their fur, paws, and in their saliva. Regular contact — petting, playing, and everyday proximity — likely increases human exposure to this microbial diversity.
What the research shows
The evidence so far suggests that people who grow up with dogs tend to show more positive social and emotional outcomes.
Taken together, the findings from the Azabu University study suggest that the mental health benefits of living with dogs extend beyond emotional comfort alone and may involve underlying biological processes.
Because the field of human–animal microbiome interaction is still relatively young, researchers emphasize that further studies are needed. Nonetheless, current findings offer a fascinating new perspective: dogs may function as a natural bridge between humans and environmental microbes, and part of what makes us feel more socially connected, caring, and emotionally attuned when we live with dogs may be rooted not only in companionship, but also in biology.
