For many pet owners, it’s no surprise that dogs greet their humans with wagging tails, excited barks, and affectionate licks. But a new study suggests there’s something even deeper happening during these reunions: dogs may actually shed tears of joy when reunited with their beloved owners.

The research, titled “Increase of tear volume in dogs after reunion with owners is mediated by oxytocin,” highlights the remarkable emotional bond between dogs and humans. Published in Current Biology, the study provides scientific evidence that dogs’ tears are linked to positive emotions triggered by their relationships with people.

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Oxytocin and Emotional Tears

According to Takefumi Kikusui, co-author of the study and a researcher at the Laboratory of Human-Animal Interaction and Reciprocity at Azabu University in Japan, dogs “shed tears associated with positive emotions” when reunited with their owners.

The hormone at the center of this discovery is oxytocin, often called the “love” or “maternal” hormone. In humans, oxytocin plays a key role in bonding and attachment. This study suggests that the same mechanism may explain why dogs cry tears of happiness when they see their owners after being apart.

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How the Study Was Conducted

Researchers worked with 22 dogs to test this emotional response. They used the Schirmer Tear Test, a standard method in veterinary practice, which involves placing a small strip of paper under the eyelid to measure tear production.

The dogs were separated from their owners for about five to seven hours. When reunited, the results showed a significant increase in tear volume compared to baseline levels, suggesting that their tears were not just a physical response, but an emotional one.

“We had never heard of the discovery that animals shed tears in joyful situations, such as reuniting with their owners,” Kikusui noted.

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Strengthening the Human-Animal Bond

Beyond the groundbreaking discovery itself, the study revealed another important effect: owners who saw tears in their dogs’ eyes reported feeling an even stronger desire to care for them. This suggests that canine tears may play a role in deepening interspecies bonding, reinforcing the emotional connection that already makes dogs such cherished companions.

“Dogs have become a partner of humans. And we can form bonds,” the researchers wrote, emphasizing that this emotional link goes both ways.

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Why It Matters

This research not only adds to our understanding of canine emotions but also strengthens the argument that dogs are capable of complex emotional expression similar to humans. The findings highlight just how deeply our pets are connected to us, emotionally as well as physically.

For dog owners everywhere, the study is a reminder of the unspoken bond we share with our pets—one that may literally bring tears to their eyes.