A 2022 study by Japanese researchers found that dogs produce tears when reuniting with their owners, which may be linked to the “bonding hormone” oxytocin.
This discovery is significant, as it is the first to show that positive emotions can stimulate tear production in non-human animals. Previous research had established that eye contact between dogs and humans releases oxytocin in both, strengthening their bond.
Inspired by this, the team, led by Professor Takefumi Kikusui of Azabu University, conducted a reunion experiment.
They measured the tear volume of 18 dogs at home and after being separated from their owners for over five hours.
The results showed a significant increase in tears when the dogs were reunited with their owners, but not with familiar non-owners. Additional tests revealed that applying oxytocin to dogs’ eyes also increased tear production, confirming the hormone’s role.
The researchers also found that humans are more inclined to care for dogs with teary eyes. In a study involving 74 participants, teary-eyed dogs triggered a 10-15% increase in nurturing responses.
The team suggests that dogs may use tears to elicit protective behaviour from their owners, although further research is needed to explore how dogs communicate with each other through tears.
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