Oxytocin may be the reason why your dog will always try to make you smile.
How often do you pet your dog? Gaze into its loving eyes? Smile at it? Hopefully, very often, because the more you do it, the more your dog will love you — and new research helps us to understand why.
Oxytocin has long been referred to as "the love hormone" and the "cuddle hormone," because we (and our pets) release it when we hug, touch, or look lovingly into someone's eyes. This increases our attachment to that person (or animal.)
But researchers already knew this. What they didn't know was that more oxytocin also makes dogs prefer smiling faces over threatening ones — kind of like we do.
This may not sound like much in the human kingdom, but among animals — which have a better chance of survival if they're attuned to threatening cues — it's kind of a big deal.
The new study was led by Prof. Outi Vainio, from the University of Helsinki in Finland, and it was published in the journal Frontiers in Psychology.
The findings seem to reinforce a virtuous circle of affection between dogs and humans: the nicer you are to your dog, the more of the love hormone they will secrete. In turn, this will make them love you even more — so much so that they might even ignore danger for your sake.
Oxytocin makes dogs love your smile
In case you're wondering how researchers could tell what a dog feels, the answer is pretty specific: by measuring the size of their pupils.
"We were among the first researchers in the world to use pupil measurements in the evaluation of dogs' emotional states," says Prof. Vainio. "This method had previously only been used on humans and apes."
Larger pupils indicated higher emotional arousal. The researchers administered oxytocin nasally to the dogs, and, using an eye-tracking device, they examined both the size of the dogs' pupils as well as the direction of their gaze.
They did so twice for each dog: once after they received oxytocin, and once without the hormone.
By default, dogs tend to focus more on the most salient aspects of a social situation — such as frightening cues in a dangerous situation. However, oxytocin seemed to make them override this survival instinct; dogs that received oxytocin were far more interested in smiling human faces than threatening ones.
This was backed by their emotional response, which was also altered. Without the hormone, they responded emotionally more to angry faces — their pupils dilated more — while when they were under the influence of oxytocin, they responded more to smiling faces.
As the authors explain, this probably means that oxytocin makes angry faces look less threatening and smiling faces more attractive. Both of these signs indicate a higher pro-social behavior.
"Both effects," says Prof. Vainio, "promote dog-human communication and the development of affectionate relations."
"It seems that the hormone oxytocin influences what the dog sees and how it experiences the thing it sees," adds doctoral student and first study author Sanni Somppi. And when that thing is your smiling face, your dog most probably loves it.