Dogs get very excited when their human families come home after a few hours away. They wag their tails. They jump up and down. A scientist in Japan recently found that some dogs may even get tears in their eyes. Tears of joy, that is!

Takefumi Kikusui is a scientist. He studies the relationship between humans and animals. A few years ago, Kikusui noticed that one of his dogs got teary-eyed as she was nursing her puppies. He wanted to find out if dogs shed tears when they are happy, like humans sometimes do. So he and other scientists measured the amount of tears dogs shed in two situations: when seeing someone they know and when seeing a member of their human family, both after being apart for a few hours. The dogs shed more tears when they were reunited with their family members than when they were reunited with other people. 

Kikusui knows that dog and human brains both make something called oxytocin in response to happiness. He found that when there is more oxytocin in a dog’s body, the dog’s eyes produce more tears. This led Kikusui to believe that dogs are shedding tears of happiness when they see their human family members after a long time apart.

It’s sweet to think dogs love their humans so much that they cry. But the tears may also help the dogs. Scientists have done studies showing that humans are more likely to give care and attention to a dog with teary eyes than a dog without tears.