Dogs Actually Shed Tears of Joy When Reunited With Their Owner, Reveals New Study

Editor’s note: This article was originally published on August 24, 2022. It has since been updated.

When it comes to love, there's nothing that can beat what a dog has to offer. Their love comes in the purest form, with no hidden agendas and that's why dogs are one of the most believed pets all over the world. Along with all the affection they have to offer, they also simply make your life better by just existing. I mean, have you seen just how happy they are to see you when you're back home after a long day at work?

But, in what is considered to be a first, it has been revealed that dogs tend to shed tears of joy when they are reunited with their owners after being separated for a long period of time.

A new study published by Current Biology revealed that the tears that form in a dog's eyes have a link to their emotion, per PEOPLE. 

"We found that dogs shed tears associated with positive emotions," said the Japanese study's author Takefumi Kikusui in a statement, hinting that the tears could be due to a release in oxytocin in dogs. 

Kikusui, a professor at the Laboratory of Human-Animal Interaction and Reciprocity at Azabu University in Japan, said that he noticed this first when one of his poodles gave birth six years ago. Her eyes welled up with tears as she nursed her newborn puppies, which ultimately led to his discovery. "That gave me the idea that oxytocin might increase tears," he said.

Known as the "love hormone," oxytocin has previously been found both in dogs and their human owners when they interact. However, the new findings suggest that the release of oxytocin cements the bond between the dog and the owner. 

"Dogs have become a partner of humans, and we can form bonds," said Kikusui. "In this process, it is possible that the dogs that show teary eyes during interaction with the owner would be cared for by the owner more."

Kikusui and his team used the Schirmer tear test, a common test, to measure the number of tears in 18 dogs to observe the connection. It involved placing a paper strip inside the dogs' eyelids for a minute before and after their five- to seven-hour separation from their owners. "Tear volume was evaluated by the length of the wet part on the STT. The baseline was about 22 mm, and the reunion with the owner increased by 10%," Kikusui told CNN via email.

The researchers then evaluated the amount of crying before and after reunions with owners and familiar individuals using 20 canines. The owner's reappearance was the only thing that made them cry more. A solution containing oxytocin was applied to the surface of 22 dogs' eyes to study the relationship between oxytocin and dog tears. After the oxytocin was applied, the tears significantly increased.

Previously, dogs have also shown that they can sense human emotions. Researchers have stated that dogs have categorized emotions such as “You are somebody I care about, therefore, I’m pleased to see you,” and “You are somebody I don’t care about, so I can ignore you most of the time,” said Dr. Daniel Mills, a veterinary behavioral medicine specialist at the University of Lincoln in England, according to The New York Times. However, he was not involved in the study by Current Biology.

Through a 2020 Canine Cottages study, researchers discovered that while hugging lowered dogs' heart rates by 23%, saying "I love you" to them increases their bpm by 46%. When owners reunited with their dogs after a long absence, their heart rates also rose by 10%. 

References:

https://www.cell.com/current-biology/fulltext/S0960-9822(22)01132-0

https://people.com/pets/dogs-shed-tears-joy-when-reunited-their-owners-study/

https://www.caninecottages.co.uk/doggy-devotion

https://www.nytimes.com/2022/08/22/science/dogs-crying-tears.html

https://edition.cnn.com/2022/08/22/world/dogs-tears-emotions-scn-wellness/

Representative Cover Image Source: Getty Images | Fernando Trabanco Fotografía