We have always been quick to see ourselves in our dogs. A gaping mouth becomes a smile. A head pressed into our lap feels like a declaration of devotion. But actual tears? That one surprised even the scientists.
The whole line of inquiry began with a Standard Poodle. About six years ago, Takefumi Kikusui noticed that while his female Poodle was nursing her puppies, her eyes would become visibly wet. They didn’t stream the way human tears do — but her eyes were clearly different, shinier and more emotional-looking, and the change seemed tied specifically to nursing. Dr. Kikusui isn’t simply a careful dog owner; he is a faculty member in the Department of Veterinary Medicine at Azabu University in Azabu Saitama, Japan, and that observation became the seed of something bigger.
What grew from it was a published study titled “Increase of tear volume in dogs after reunion with owners is mediated by oxytocin” — and it landed on three significant findings.
Dogs produce more tears when reuniting with their owners
After a separation of several hours, dogs tear up more when greeting their owners than they do when spending ordinary time together at home. They also produce more tears reuniting with their owners than with other familiar people. The increase in tear volume during reunions points to an emotional origin for the response. This matters because, before this research, no scientific evidence existed connecting dog tears to feelings of any kind. Humans cry from a range of emotions — sadness, joy, frustration, even rage — and everybody knows it. What this study demonstrated for the first time is that another species does something similar.
Although the increased tear production is small, it is noticeable. Kikusui emphasized that it was a difference in visual appearance that prompted his research in the first place: “If the owners are sensitive, they can recognize it. Initially, my female Standard Poodle got pregnant, and she gave milk to the puppies (meaning higher oxytocin secretion), her eyes were shining, and [her] face became cuter; we recognized it and started this experiment.”
Oxytocin causes the tears
When researchers applied oxytocin to dogs’ eyes, tear production increased compared to a control substance of similar structure. Oxytocin — widely called the “love hormone” — is already known to play a central role in romantic pair bonds, maternal bonding, and the deep connection between humans and dogs. Petting a dog raises oxytocin levels in both the person and the animal. The act of nursing also triggers oxytocin release, which is exactly why Kikusui credits watching his Poodle nurse her puppies with giving him “the idea that oxytocin might increase tears.”
The fact that oxytocin drives the tear response strengthens the case that dogs are producing tears in response to emotional states, not simply as a physiological reflex.
People feel more warmth toward dogs with misty eyes
In another arm of the research, study participants were shown photographs of dogs with and without artificial tears added. They consistently responded with more nurturing feelings toward the wet-eyed dogs. This finding suggests a functional advantage: if misty eyes prompt humans to feel more love and protective instincts toward a dog, then an emotional tear response could help reinforce and deepen the bond over generations.
Eye contact between humans and dogs already increases oxytocin on both sides. Adding visible emotion to that exchange may intensify what’s already a powerful feedback loop between the two species.
Dogs shed tears of joy
“We found that dogs shed tears associated with positive emotions,” Kikusui says. “Their tears might play a role in the deepening of mutual relationships and further leading to interspecies bonding.”
That’s the part that might get you a little misty yourself. If knowing that your dog’s eyes are welling up with happiness when you walk through the door doesn’t deepen your sense of the relationship you have with them, nothing will.
