If you’re a dog owner, coming home from work or running errands to your dog’s enthusiastic greeting can be one of the best parts of your day. Besides their wildly wagging tails and tapping toes, there’s an excited glint in their eyes. They missed you just as much as they missed you. According to a new study, that sparkle in their eyes might actually be tears — tears of joy at being reunited with you.
According to a new study in Current Biologydogs, like humans, produce tears when they are overwhelmed with emotion – especially when they are reunited with their owners.
“We found that dogs shed tears associated with positive emotions,” said Takefumi Kikusui of Azabu University in Japan in press release. “We also identified oxytocin as a possible mechanism underlying it.”
Kikusui first made the connection after his dog had a litter of puppies. He noticed that his dog had tears while she was nursing her puppies. The authors mention that although their tears don’t fall as often as humans, dogs do have watery eyes.
“This gave me the idea that oxytocin could increase tears,” Kikusui says in a press release.
Oxytocin is a hormone that controls reproduction, among other things. The hormone it can make you feel closer and more connected to a loved one and can be experienced through music, physical touch and even exercise.
According to the study authors, oxytocin is released in both dogs and their owners when they interact. To determine whether oxytocin causes a dog to produce tears, the researchers conducted a test pairing dogs and their owners.
The first test measured the tears in the dogs’ eyes before and after they were reunited with their owner versus a stranger. Tear volume increased in their owners, but not in strangers.
Second, the researchers added oxytocin to the dogs’ eyes when they weren’t around their owners, and tear production also increased. This shows that when a dog naturally produces oxytocin – such as when it sees its owners – its eyes water.
The research team also presented people with pictures of dogs and asked them to rate which pictures they liked best. Most participants preferred the watery-eyed dogs over the dogs, not suggesting that watery-eyed dogs help build a stronger bond with humans.
“We had never heard of the discovery that animals shed tears in joyful situations, such as being reunited with their owners, and we were all excited that this would be a world first!” Kikusui said in a press release.
The study shows that dogs produce tears associated with positive emotions, although it is not clear whether dogs produce tears associated with negative emotions. It is also unclear whether dogs produce tears when reunited with other dogs.
“Dogs have become partners to humans and we can form bonds,” Kikusui said in a press release. “In this process, it is possible that dogs that show watery eyes during owner interactions may be cared for more by the owner.”