Dogs Actually Tear Up When Their Owners Come Home

Karen Hopkin: This is Scientific American’s 60-Second Science. I’m Karen Hopkin.

After an exhausting day at the office, it’s hard not to smile when you’re greeted by a delirious display of uncontrolled canine joy.

[Dog greeting]

But it’s not just the happy yapping and wriggling tail wagging that tug at our heartstrings.

[Dog greeting]

Because a new study shows that dogs’ eyes fill with tears when reunited with their people…an effect that evokes our nurturing instincts. The findings appear in the journal Current Biology.  

Takefumi Kikusui became interested in doggies’ damp and adoring gazes while watching his pet poodle interact with her pups.

Takefumi Kikusui: When she was nursing her puppies, her face becomes so cute. Of course she’s so cute as always. But more.   

Hopkin: At some point Kikusui, who’s a professor of veterinary medicine at Azabu University in Japan, realized that his adorable mama dog had tears in her eyes. That potential connection between unbearable cuteness and unshed tears sent Kikusui scurrying away from his poodle and back to the lab.

Kikusui: In the test, we initially measure the baseline tear volumes when dogs were together with the owner in their house.

Hopkin: Then the owner would high-tail it off for five or six hours.

Kikusui: When the owner came back, we measure tear volume again. And found that the reunion with the owner stimulate tear secretion.

Hopkin: But it only worked with the dog’s owner.

Kikusui: There was no increase in tears when the dogs were separated from the owner and reunited with the dogs’ caretaker in a dog care center.

Hopkin: The researchers suspected that the tearful reaction was stimulated by oxytocin…a hormone associated with social bonding. They had shown previously that oxytocin is boosted when dogs interact with their owners. And oxytocin receptors have been found to be abundant in the glands that secrete tears in mice.  

Kikusui: So we applied oxytocin to the dogs’ eyes.

Hopkin: And voila…the dogs grew weepy. But to what end? In other words, is there some benefit to this lachrymose behavior? To find out, Kikusui and his colleagues showed volunteers a couple of hound head shots.

Kikusui: One was a normal dog face. And the other was teary dog face in which we added artificial tears.  

Hopkin: The volunteers were more likely to want to cuddle and care for the mutts with big, wet puppy-dog eyes…

Kikusui: …suggesting that teary eyes of dogs can facilitate the human caregiving behavior.

Hopkin: So dogs turn on the waterworks and their owners roll over. Now, that’s quite a clever trick!

[Dog greeting]

Hopkin: For Scientific American’s 60-Second Science, I’m Karen Hopkin.

Kikusui: Thank you for listening.

[The above text is a transcript of this podcast.]