You know your dog loves you just as much as you love them, but there’s more scientific proof of this fact, just in case you needed it. Researchers at the Laboratory of Human-Animal Interaction and Reciprocity at Azabu University in Japan studied the link between emotions and tears in dogs. The results suggest that dogs produce emotion-elicited tears when reunited with their owners after an extended separation.
Six years ago, Professor Takefumi Kikusui noticed his poodle had teary eyes when nursing her newborn puppies.
“That gave me the idea that oxytocin might increase tears,” Kikusui, who authored the study, said in a statement.
He explained that oxytocin is known as the maternal or love hormone. He and other researchers had also learned that oxytocin is released during interactions between dogs and their owners, leading them to explore a reunification experiment.
Using a standard test to measure dogs’ tear volume, they calculated tears before and after reuniting with their owners. They also compared the tears dogs shed when interacting with someone they didn’t know. They found that tear volume increased when they reunited with a familiar human but not with a stranger.
As part of the study, in Current Biology, authors included a video (below) of a participant arriving home to her dogs. “Two dogs, especially a standard poodle named Kochi, showed excitement and great joy when the owner returned home after 6 months of absence,” the authors wrote. “The dogs and owner both showed emotional arousal.”
Next, they added oxytocin to the dogs’ eyes. Again, they found the tear volume increased, supporting the hypothesis that the release of oxytocin plays a role in tear production when dogs are rejoined with their humans.
“We found that dogs shed tears associated with positive emotions,” Kikusui said. “We also made the discovery of oxytocin as a possible mechanism underlying it.”
Finally, they asked people to rate pictures of dogs’ faces with and without tears in their eyes. The people surveyed gave more positive responses to teary-eyed dogs, suggesting that tear production helps to develop stronger connections between people and their dogs.
Kikusui said that he was surprised by the findings.
“We had never heard of the discovery that animals shed tears in joyful situations, such as reuniting with their owners, and we were all excited that this would be a world first!” he said.
The researchers have not yet tested dogs’ tear production in response to negative emotions or when they are reunited with other dogs. However, the research further proves the strength of the bond between dogs and humans.