Dogs shed tears of joy when reuniting with their owners: study

A study conducted by researchers in Japan found that dogs produce tears of joy upon being reunited with their owners after just hours of separation.

The findings, which have been published in the journal Current Biology, detail how a hormone called oxytocin makes a dog bond with its owner. The hormone is also known as the "love hormone" and is released in large amounts when a woman undergoes labour or when a person falls in love.

The researchers conducted a test called a Schirmer Tear Test on a group of 22 dogs for the study. The test measures the volume of tears shed by the animal. It involves placing a strip inside the eyelids of the dogs for a minute before and after they are reunited with their owners.

They found that the amount of tears produced by dogs increased significantly when they were reunited with their owner compared to someone they were only familiar with.

"We had never heard of the discovery that animals shed tears in joyful situations, such as reuniting with their owners, and we were all excited that this would be a world first," said Takefumi Kikusui, a co-author of the paper.

"We found that dogs shed tears associated with positive emotions. We also made the discovery of oxytocin as a possible mechanism underlying it," he added.

To understand the role of oxytocin, the researchers applied the hormone to the dogs' eyes and found that it increased the volume of tears produced significantly when compared to the results achieved after applying a control solution.

The researchers added that unlike other animals, dogs have acquired the ability to communicate with humans through eye contact, and that is what makes humans care for them. "Through this process, their tears might play a role in eliciting protective behaviour or nurturing behaviour from their owners," read the paper.

However, the sample size for the current study was quite small, and scientists believe that more studies need to be conducted to consolidate the findings.