This story was first published on August 23, 2022. This was republished on June 6, 2023.

Dogs can well up with tears of joy when they are reunited with their human buddies, international research has found.

Six years ago, Takefumi Kikusui, a Japanese researcher from Azabu University, noticed one of his poodles would get teary eyes when she nursed her puppies. 

He wanted to know whether, like humans, dogs can also cry happy tears.

His research team measured the volume of tears in a group of dogs' eyes before and after reuniting them with their favourite human, and again when introducing them to a stranger. 

They found the dogs had more tears when reuniting with a loved one but not when meeting a stranger, suggesting dogs can cry tears of joy when they see their human.

“We found that dogs shed tears associated with positive emotions,” Kikusui says. “We also made the discovery of oxytocin as a possible mechanism underlying it.”

Oxytocin is known as the maternal or “love hormone”. When the researchers added oxytocin to the dogs’ eyes, their tear volume increased. 

Kikusui says the findings came as a surprise. 

“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 says.

“Dogs have become a partner of humans, and we can form bonds. 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.”

Research is yet to test whether dogs produce tears in response to negative emotions as well. It also isn’t clear if dogs produce tears when reuniting with other dogs. 

Top image: Happy dog and owner reunited. Photo supplied: Madoka Nakamura.

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