A recent study published on August 22, 2022, in Current Biology, shows that dogs produce tears of joy when they are reunited with their human. We are talking about a world first, carried out by researchers from Azabu University in Japan, as no other scientific study explore this topic.

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All dog owners experience joyful reunions daily with rapid tail-wagging, vocalizations, leaps of joy, and unstoppable licks. But who would have thought that dogs express such positive emotion in more subtle ways?

The scientists measured the number of tears produced using a strip placed under the eyelid (Schirmer test). Baseline data was collected when the dog was in the presence of its human and in its usual environment. After five to seven hours of separation, the number of tears increased significantly within five minutes of the dog reuniting with its owner.

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The amount of tears was also higher when the dog found its human, rather than another person. According to the researchers, this production of tears is linked to the presence of oxytocin, nicknamed the hormone of love.

They also sought to understand the reason that led dogs to adopt this mechanism. To do this, owners were asked to rank photos of their dog indicating how much they made them want to take care of their companion. According to the study, photos where the artificial tears had been administered to the animal were ranked “significantly” higher.

“It’s possible that dogs who exhibit misty eyes during their interactions with their owner may lead their human to take care of them more.” – Takefumi Kikusui, Azabu University.

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In humans, a baby crying will lead parents to pay more attention to them. Dogs, domesticated like no other animal, have developed this specific communication skill over time. Also, eye contact has been shown to play a role in forming a relationship between a dog and its human.

The researchers at the Azabu University hope to study whether dogs also produce tears when they find other conspecific.