Owning a dog has long been celebrated for the happiness it brings – wagging tails at the door, playful companionship, and the comfort of a loyal friend. Now, scientists say the joy may run deeper than emotions alone. A new study from Japan suggests that dogs influence their owners’ mental health — especially that of teenagers — by sharing microscopic organisms that reshape the human microbiome, the trillions of bacteria living in and on our bodies. These microbial shifts appear to promote empathy and prosocial behaviour, adding a new dimension to the age-old relationship between humans and dogs.
For many parents, the benefits of dog ownership are visible in everyday life. “My son became more outgoing after we brought home Ginger, a labrador,” says Anitha Ravi, a mother of two in Kochi. “He talks more, plays with friends, and even seems calmer during exams. We thought it was just the bond with Ginger.”
Aravind Nair, a father in Thiruvananthapuram, shares a similar experience. “My daughter was shy and withdrawn. After we adopted Coco, a native breed, she started taking him for walks, meeting neighbours, and even volunteering at school events. It’s as if the dog opened a door to her social world.”
These anecdotes echo the findings of researchers at Azabu University, who analysed oral microbiome samples from 13-year-olds with and without dogs at home. While both groups showed similar diversity of microbes, the composition differed: dog-owning teens had specific bacteria linked to prosocial behaviour. When these microbes were transplanted into laboratory mice, the animals displayed more social interaction, sniffing and engaging with cage mates more often.
“The most interesting finding from this study is that bacteria promoting prosociality, or empathy, were discovered in the microbiomes of adolescent children who keep dogs,” says study leader Takefumi Kikusui in a statement.
The Japanese team’s work builds on earlier studies showing that people raised with dogs score higher on measures of companionship and social support. Other research has found differences in gut microbiomes between dog owners and non-owners. The gut microbiome is increasingly recognised as a key player in mental health, influencing mood, resilience, and social connect.
“Dogs influence their human masters’ gut microbiome through increased microbial diversity. Dogs bring in environmental microbes into the home from various sources such as soil and grass,” says Dr Sanjay D, nodal officer for One Health and deputy director of animal husbandry department in Kerala.
While the benefits are compelling, experts caution against over-generalising. Dr Sabu Thomas, director of the Centre of Excellence in Microbiome, Thiruvananthapuram, emphasises the need for a holistic approach. “Studies on this subject should follow a One Health approach, since humans, animals, and the environment are all interconnected. Human health can improve when probiotic bacteria are transferred from dogs, and the microbiome does play a role in well-being. However, a single study cannot prove that all pet owners will benefit in the same way. We should avoid generalising the findings and remain cautious about the risks of pathogen sharing.”
This perspective highlights the complexity of microbial exchanges. While dogs may introduce beneficial bacteria, they can also carry pathogens. The balance between health benefits and risks depends on factors such as hygiene, veterinary care, and environmental conditions.
Dr Sanjay underscores the importance of caution, especially in the context of climate change. “There is also a risk of contracting zoonotic diseases. It is important that dogs are dewormed and vaccinated. The risk aspects should not be underemphasized.”