Dogs cry tears of joy when reunited with their owners

Everyone is familiar with the human reaction to a wailing infant. These tears evoke in us an instinctive urge to comfort and console, as well as to provide the necessary care. What if, though, our dogs also sobbed in response to emotional stimuli? Would that generate a caring response from a human? Until Takefumi Kikusui noted a small difference in his standard poodle after she had puppies, no research had apparently been conducted on tear production in dogs or any other species. Every time she nursed them, her expression altered, and she had tears in her eyes.

Kikusui pondered whether his dog’s oxytocin levels were responsible for this emotional response. This hormone, he added, is known as the “love hormone” or “maternal hormone” and is essential for the creation of bonds between mother and child, as well as in other relationships.

Prior study has demonstrated that a dog’s gaze promotes the release of oxytocin in its owner, as well as an increase in oxytocin levels in dogs when they are reunited with their owners. Kikusui pondered whether oxytocin was responsible for his dog’s watery eyes while she fed her babies. “This led me to believe that oxytocin may stimulate tear production,” stated Kikusui of the Azabu University in Japan.

First, the researchers examined whether dogs produced more tears in response to the emotional experience of being reunited with their owner. Using the usual Schirmer Tear Test (STT), the researchers examined tear volume in dogs when they were at home with their owner and again within five minutes of being reunited with the owner after a separation of between five and seven hours.

When reunited with their owner, the 18 dogs in the study generated far more tear fluid than when they were merely relaxing at home. In addition, a bigger volume of tear fluid was produced when animals were reunited with their owners, but not when they were greeted by a familiar non-owner. While dogs do not weep in torrents of tears like a human infant in anguish, their eyes become moist as the volume of tear fluid increases.

Kikusui stated that the findings were unexpected. We had never heard of the revelation that animals cry in happy situations, such as when they are reunited with their owners, and we were all thrilled that this would be a world first!

To evaluate the effect of oxytocin in tear generation in dogs, researchers applied oxytocin solutions to the eyes of some dogs while others received a control peptide containing the same amino acids in a different arrangement. Measuring tear volume revealed a considerable increase in tear production following oxytocin administration, but not following administration of the control peptide solution.

“We discovered that dogs shed tears in response to happy feelings,” explained Kikusui. In addition, we discovered oxytocin as a possible underlying mechanism.

In the final portion of their experimental investigation, the researchers examined whether individuals are more inclined to care for dogs with teary eyes than for dogs with normal, tearless eyes. Participants were shown images of dogs, some with artificially teary eyes and others without, and were asked to rate the likelihood that they would wish to care for each dog.

People were substantially more inclined to desire to care for dogs with tears in their eyes than normal, tearless canines, according to research published in the journal Current Biology. These results imply that dogs’ tear production strengthens the bond between humans and their canines.

According to the authors, dogs appear to shed tears in settings that humans would deem “pleasant.” They have not yet examined whether dogs respond similarly to negative emotions. Additionally, it is unknown if dogs shed tears when reunited with other canines. They seek to determine whether this response has a social role in the world of dogs. For the time being, though, it appears to have significant consequences for the dog-human bond.

“Dogs have become man’s companion, and we may build ties with them,” stated Kikusui. “In this process, it is feasible that owners may care for their dogs more if they have teary eyes during interactions with them.”