It’s not just a human emotion. Dogs can cry for joy too. Especially when they are reunited with their owners. The journal ‘Current Biology’ published an article about it.
“We found that dogs shed tears associated with positive emotions.” Takefumi Kikusui of Azabu University (Japan) explains. “We also made the discovery of oxytocin as a possible underlying mechanism.”

More tears
Kikusui and his colleagues made the discovery after one of their two poodles had puppies 6 years ago. When their dog suckled the puppies, tears appeared. They didn’t fall the way they usually fall in humans, but they did get tears in their eyes. “That gave me the idea that oxytocin might increase tears,” Kikusui says.
Oxytocin, he explains, is known as the maternal or “love” hormone. It is known to be released in both dogs and their owners during interactions. They decided to conduct an experiment. They found that the volume of tears increased when they met the familiar human. Not so with a person they did not know. When they added oxytocin to the dogs’ eyes, their tear volume also increased.
Volunteers rated photos of the dogs’ faces with and without artificial tears. It turned out that people gave more positive responses when they saw dogs with teary eyes. Tears help forge stronger connections between people and their dogs.

Other emotions
Kikusui says the findings came as a surprise. “We didn’t know that animals shed tears in joyful situations, such as being reunited with their owners. This is a world first.”
They do not yet test whether dogs produce tears also in response to negative emotions. Or if it happens when they get together with other dogs. They hope to find out if this response also has a social function in the canine world. For now they say it seems to have clear implications for the dog-human bond.
“Dogs have become companions for humans. We form bonds,” says Kikusui. It is possible that dogs that show teary eyes during interaction with the owner are more cared for by the owner.” Dogs can cry with joy. Another thing that brings them closer, once again, to humans.