If you’re a dog person, you already know how loving and loyal our four-legged friends can be. But science just confirmed it in a new, heart-melting way — a research study showing that dogs cry actual tears when reunited with their owners after even a short amount of time.
A team of Japanese scientists placed paper filters on the lower eyelids of 18 dogs to measure how much moisture they produced after getting to see their person again after five to seven hours. The difference was marked, with the dogs producing more tears in the five minutes after being reunited than their baseline amount of tears.
The scientists linked this to the production of oxytocin, sometimes known as the love hormone.
“This is the first report demonstrating that positive emotion stimulates tear secretion in a non-human animal, and that oxytocin functions in tear secretion,” the team wrote.
To test this further, they actually put oxytocin in another group of dogs’ eyes to see if more tears were produced, and they were. They then compared this with putting another solution in the dogs’ eyes to confirm that more tears were not produced in that instance.
Humans also underwent testing related to this study, looking at photos of dogs and rating how they reacted to them — whether they wanted to care for them or not. The dogs with tears in their eyes generally rated higher, suggesting that not only do dogs cry happy tears when they see their owners, but that it serves to endear their caretakers to them further, which is ultimately beneficial to their well-being.
“Unlike any other animals, dogs have evolved or have been domesticated through communication with humans and have gained high-level communication abilities with humans using eye contact,” the study reads. “Through this process, their tears might play a role in eliciting protective behavior or nurturing behavior from their owners, resulting in the deepening of mutual relationships and further leading to interspecies bonding.”
Interestingly enough, dogs did not produce the same increase of tears when being reunited with humans they were familiar with who were not their owners, but the study notes “sniffing and licking near the eyelid is commonly observed behavior when dogs greet one another, suggesting a possibility that dogs’ tears also play a role as a social signal.”
Whatever the biological reasons behind it all, the take away for human dog lovers is clear — our dogs are thrilled to spend time with us after being separated, and they’re wired to make sure we know it and only come to love them even more.