Science suggests dogs actually cry happy tears when their people return home

My dog, Stevie, and I have a coming home ritual. When I walk in the door, I sit down on the ground so she can get close to me, and then she lays down and cries. Despite the fact a lot of science is critical of the idea that we can understand canine emotions, I’ve always read Stevie’s reaction to my homecoming as real joy. A new study suggests I could be right. As it turns out, dogs may actually cry tears of joy when they’re reunited with their people.

The study, which was published Monday in Current Biology, analyzed the volume of tears of 18 pups. First, the researchers measured the volume of tears the dogs regularly produced, and then compared those measurements with the volume of tears that the same dogs produced five minutes after being reunited with their caregivers after a workday length separation — five to seven hours.

What researchers found was that the dogs produced about 10% more tears after the reunion. This is extraordinary because, until now, we haven’t really understood much about how dogs experience feelings, and most scientists have stuck on the idea that humans are the only animals that cry for emotional reasons. We’ve always known that dogs shed tears to keep their eyes lubricated, but it seems no one has thought to study whether or not they cry emotional 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!” Takefumi Kikusui, a professor at Azabu University in Japan and one of the study’s co-authors, said in a news release published by EurekAlert.

Kikusui spearheaded the research when he noticed that his own dog, a poodle, had unusually wet eyes after having a litter of puppies. “That gave me the idea that oxytocin might increase tears,” Kikusui said. Oxytocin — a.k.a. “the love hormone” — is a hormone animals make in bonding situations that, in combination with other hormones, makes them feel happy and connected to others.

It turns out Kikusui’s instincts were right. When scientists put a solution containing oxytocin into the dogs’ eyes, they produced significantly more tears, according to the study. And it seems that you can’t fake a bond, either; when the scientists measured tears after dogs interacted with strangers, there was no measurable change.

Not every animal scientist is on board with this whole tears of joy idea, though. Daniel Mills, a veterinary behavioral medicine specialist at the University of Lincoln in England who was not involved in this study, told The New York Times that it’s more likely that what this study proves is that dogs may produce more tears in order to garner a sympathetic response in humans, not that they’re having their own emotional response. “It might be that things like a more glossy eye or the presence of tears do encourage nurturing tendencies in us,” Mills told the NYT.

This new study is small and will require a lot more research to really prove its hypothesis — but personally, I believe that Stevie cries when she sees me because we are in love. I am a hardcore science stan, but after living with animals my entire life, there is no doubt in my mind that the bond between us is real. I’m not crying, you're crying. And Stevie’s crying, too.