Dogs Shed Actual Tears of Joy When Reunited with Their Owners, Study Finds

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Dogs have once again proven to be human's best friend.

A new study published by Current Biology finds that dogs' eyes well up with tears when they're reunited with their owners after long periods of separation, potentially linking their tears to emotions for the first time.

"We found that dogs shed tears associated with positive emotions," said the study's author Takefumi Kikusui in a statement, noting that the tears may be due to a release of oxytocin.

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Kikusui, a professor at the Laboratory of Human-Animal Interaction and Reciprocity at Azabu University in Japan, made the discovery after one of his poodles gave birth six years ago, and tears began welling up in her eyes as she nursed. "That gave me the idea that oxytocin might increase tears," he said.

Oxytocin, which is also known as the "love hormone," has previously been found in both dogs and their human owners during interactions. The new findings suggest that the release of oxytocin solidifies the bond between humans and dogs.

"Dogs have become a partner of humans, and we can form bonds," said Kikusui. "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."

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The study comes after scientists found that dogs' heart rates increase by 46 percent when their owner says "I love you," while cuddling brings down their bpm by 23 percent, according to a 2020 Canine Cottages study. Their owners' heart rates also increased by 10 percent when reunited with their dogs after a long period of time.

Researchers also determined that the phenomenon known as "puppy dog eyes" was likely achieved through thousands of years of selective breeding to give dogs more human-like faces, according to a study released in April.