Dogs and humans clearly have a special bond. But do dogs, like humans, produce more tears at times when they are flooded with emotion? A new study by Japanese researchers—which may be the first to look at this question—says that, indeed, the eyes of our canine companions do well up with tears. In fact, it happens regularly when they’re reunited with you.
“We found that dogs shed tears associated with positive emotions,” said Professor Takefumi Kikusui of Azabu University.
“We also made the discovery of oxytocin as a possible mechanism underlying it.”
Professor Kikusui and colleagues made the discovery—reported in Current Biology—after one of his two standard poodles had puppies six years ago. He noticed that when his dog was nursing the puppies, something changed in the dog’s face; there were tears. Those tears don’t fall as they often do in humans, but they do get tears in their eyes.
“That gave me the idea that oxytocin might increase tears,” Professor Kikusui said.
Oxytocin is known as the maternal or ‘love hormone’. The researchers also knew from earlier observations that oxytocin is released in both dogs and their owners during interactions. So, they decided to run a reunification experiment and see if it brought dogs to tears.
First, they used a standard test to measure dogs’ tear volume before and after reuniting with their owners. They found that tear volume did indeed increase when they got back together with the familiar human as opposed to a person they didn’t know.
When they added oxytocin to the dogs’ eyes, tear volume also increased. That finding supports the idea that the release of oxytocin plays a role in tear production when dogs and their owners are reunited.
They also asked people to rate pictures of dogs’ faces with and without artificial tears in them, and it turned out that people responded more positively when they saw dogs with teary eyes. These findings suggest that dogs’ tear production helps to forge stronger connections between them and their owners.
The findings seem to have clear implications for the dog-human bond.
“Dogs have become a partner of humans, and we can form bonds,” Professor Kikusui said.
“In this process, it is possible that the dogs that show teary eyes during interaction with the owner would be cared for by the owner more.”
