Dogs Cry Tears of Joy When Reunited With Their Humans, Study Finds

A soldier and his dog are reunited after a long time apart
Dogs can show emotional tears when seeing their humans after a long time apart, scientists report. Pekic / E+ / Getty Images
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Humans and dogs have been enjoying a symbiotic relationship of nurturing and trust for tens of thousands of years. Dogs make people feel safer and loved and humans nurture their canine companions, providing them with a warm place to sleep, affection and treats. The result is a significant and lasting bond.

With all the love that connects humans and pooches, scientists wondered if the canine half of the equation teared up more when they experienced a flood of emotion like humans do.

According to new research, the answer is yes, the eyes of pups do flood with tears on a regular basis when they get emotional, like when they’re reunited with their humans, reported Phys.org.

“We found that dogs shed tears associated with positive emotions,” said Takefumi Kikusui, a professor at the Laboratory of Human-Animal Interaction and Reciprocity at Azabu University in Japan, who is co-author of the research, as CNN reported. “We also made the discovery of oxytocin as a possible mechanism underlying it.”

The results of the study, “Increase of tear volume in dogs after reunion with owners is mediated by oxytocin,” were published in the journal Current Biology.

Six years ago, Kikusui discovered that when his poodle was nursing her puppies there were tears in her eyes. That made Kikusui think that the “love hormone” oxytocin might cause an increase in tear production.

The research team already knew that dogs and humans release oxytocin when they interact. They measured the volume of tears the dogs had before and after they reunited with their humans and found that when they reconnected with them their tear volume increased. However, when the pups connected with someone they weren’t familiar with, they did not produce more tears.

“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,” said Kikusui, as reported by Phys.org.

The team went further, adding oxytocin to the eyes of the dogs, which also increased the amount of tears their eyes produced. This supported the hypothesis regarding oxytocin and tear production.

In the study, the researchers asked people to look at photos of the faces of dogs with artificial tears and those without and rate them. More positive answers were given in response to the photos of dogs with tears in their eyes, which suggested that the production of tears supports more powerful connections between dogs and humans.

“Dogs have become a partner of humans, and we can form bonds,” said Kikusui, as Phys.org reported. “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.”

The research team hasn’t yet looked into whether dogs produce tears when they’re unhappy. They also don’t know if they do so when they’re reunited with their canine friends, but hope to find out.

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