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Does Your Dog Cry Tears of Joy When You Get Home?

New research on happy tears in dogs and their role in dog-human interactions.

Key points

  • Tear volume increased in dogs when reunited with their owners after a separation.
  • Tear volume did not increase after separation and then reunion with a non-familiar person.
  • Researchers believe that dog tears may be a socio-communicative behavior that elicits caregiving from humans.
Sophie Elvis/Unsplash
Source: Sophie Elvis/Unsplash

Your dog is probably happy to see you when you’ve been gone for a while. Maybe she barks, jumps, wags, and maybe even pees a little on the floor. But is she so happy that she cries tears of joy? Research published this week in Current Biology suggests that this might just be the case.

Humans cry in a whole range of emotionally arousing situations, not only when we are sad or in pain. Think of the marathon winner, tears streaming down her face as she stumbles across the finish line, the mother who cries when her child performs in the school play.

A research team from Japan wanted to explore whether a relationship between tears and positive emotional arousal is also present in other animals, specifically dogs. Do dogs cry “tears of joy” when feeling strong positive emotions? To explore this question, the researchers tested a specific hypothesis: that dogs would secrete tears when reunited with their owners after an absence, and that tear secretion is mediated by oxytocin. Oxytocin is known colloquially as the “love hormone” because it plays an important role in the formation and maintenance of social bonds. The results were published in Current Biology this week and add yet another fascinating piece to the puzzle of who dogs are and how humans and dogs fall in love.

The researchers did a four-part experiment involving companion dogs. First, using something called the Schirmer tear test, they measured the baseline tear volume of the dogs in the normal home environment with the owner present. They then measured tear volume within the first five minutes of the dogs being reunited with their owner after a five- to seven-hour separation. Tear volume increased significantly during the reunions.

Second, the researchers looked at dogs in a doggie daycare center and compared the tear volume of dogs after separation and reunion from their owner and from a non-familiar human. Tear volume was greater after reunion with owners than with non-familiar people.

Next, the researchers applied an oxytocin solution to dogs’ eyes (not a painful or harmful procedure), to see whether oxytocin might mediate tear secretion during owner-dog interactions. When oxytocin increased, tear volume also increased.

Finally, the researchers had a group of human participants look at photos of dogs with or without artificial tears in their eyes. Participants assigned more positive scores to photos with tearful dogs, suggesting that dog tears elicit a positive human emotional response.

Tear production is one piece of a much larger set of socio-communicative capacities that have evolved in dogs to facilitate interaction with humans and to elicit caregiving behavior from humans. Dogs use eye contact with humans to elicit caregiving behaviors and have facial musculature that allows them to raise their inner eyebrows into the irresistible “puppy dog eyes” to tug at our heartstrings and convince us to give over a few bites of our sandwich. When our dog gazes at us, it triggers a release of oxytocin in our brain—and in theirs.

Next up: Might tears also play a social-facilitative role in relationships between humans and other domesticated animals who live in close friendships with us, such as cats and horses?

Also, we need research looking at the human side of this: Do humans cry tears of joy after a long separation from their dog? (From personal experience, I’d say “highly likely.”) Does human tear production elicit caregiving behaviors from dogs?

References

Murata, Kaori et al. “Increase of tear volume in dogs after reunion with owners is mediated by oxytocin.” Current Biology, Volume 32, Issue 16, PR869-R870. https://doi.org/10.1016/j.cub.2022.07.031

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