Your dog can cry tears of joy, just like you do

We humans have learned to recognise what some animal behaviours mean and how they are communicating with us. We try to find similarities between them and us. Now, new research says that dogs can cry 'tears of joy'.

For the record, if you don't know, humans are the only creatures on Earth that are known to shed emotional tears. Before this research, it was largely known that only humans could weep with tears for reasons other than physical pain and other natural processes like keeping the eye clean. 

So, have dogs made it to the list of animals that can cry for emotional reasons? 

Japanese researchers published a paper in Current Biology on August 22, 2022, which claims that they found our canine companions capable of shedding emotional tears. It is already known that tear volume in humans increases during emotional arousal; the study answers the question of whether it is the same for dogs.

"We found that dogs shed tears associated with positive emotions. We also made the discovery of oxytocin as a possible mechanism underlying it," Takefumi Kikusui of Azabu University in Japan, a co-author of the paper said in a statement.

How was the study conducted? 

1. The study sought to investigate 'the relationship between emotional arousal and tear volume in animals'. 
2. They conducted the Schirmer tear test (STT) to measure tear volume in dogs before and after their reunion with human parents and familiar non-parents. 
3. It also studied whether oxytocin (popularly known as the love hormone) was behind the tear volume increase. As part of the study, oxytocin solution was applied to the dogs' eyes.
4. Humans were also asked to rate their photos of dogs with or without artificial tears.

What did the study find? 

1. "Tear volume increased significantly during the reunion with the owner, but not with a familiar non-owner," the study said in its conclusion. 
2. Application of oxytocin solution increased tear volume, suggesting that the hormone might be impacting tear secretion. 
3. It was also found that humans gave more positive scores to the photos of dogs with artificial tears. The researchers say this suggests emotionally driven tears in dogs can help human-dog communication.

Limitations: This is a preliminary study. So, more research in this area is required to absolutely say whether dogs can cry like humans.  

And the last point about the human impression of dogs needs to be noted. It indicates that even if it is absolutely true that dogs shed emotional tears, it could be a result of centuries of domestication of the canines by humans. Our pet dogs and even cats may have learned that humans respond better to their needs if their eyes well up (cue: the puppy eyes).

So, unknowingly, humans may have been the ones to breed dogs to shed emotional tears. 

What we already know: We know that animals - dogs, cats, elephants, etc. - can feel a range of emotions from sadness to happiness. Animals also have developed ways to communicate with others about their emotions. Howling, leaving specific scents, and now perhaps eyes welling up are some of the ways animals display the emotions they are feeling. 

Animals including our pets are known to have teary eyes. But the teary eye in animals is often associated with reasons such as a lubricant for the eyes, cleaning of the eyes, etc. So, if the tears are coming too often and streaming down the face, it is usually a sign that their eye health may be deteriorating, and it's time to a visit to the vet. Dogs, in particular, have a mechanism that sucks their tears back in and the tears don't fall down their face. So, even if their eyes are welling up due to an emotional response, their tears shouldn't be running down.  

Researchers still do not fully know why and how humans cry as they do.