Smile! Your Dog Loves It

It’s been well documented that oxytocin, a powerful hormone produced in the hypothalamus, has physical and psychological effects in humans that influence our emotional and social behaviors. And now the same can be said for our canine companions. In fact, your smile alone could entrance your dog in such a way that it may neglect its natural instinct to avoid dangerous situations—thus proving that your relationship is based on science and not just puppy love.

A study conducted by Finnish and Hungarian reseachers found that oxytocin—also known as the “affection drug”—made dogs interested in smiling human faces while also making them see angry faces as less threatening. Dogs that received intranasal oxytocin, as opposed to saline solution, fixated on the eyes of happy faces significantly more often than on the eyes of angry faces.

The experiments were set up in 4 phases and included 43 dogs of varying breeds and sexes that ranged in age from 1 to 10 years. Throughout the study, which was conducted from August through October 2012, none of the dogs was on medication and daily routines were kept similar to those in their regular lives.

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First, the dogs were brought to the test room for initial trials where they viewed photos of landscapes and wild animals while being rewarded randomly. Following this warm-up phase, the dogs were brought to a separate room where they received either an oxytocin or placebo nasal spray treatment. After the treatment, the dogs waited in their owners’ car or in a separate room without social stimulation. The dogs were then brought back into the testing room and shown pictures on a computer screen of the same, unfamiliar male face. Images of the man making one happy face and one angry face were presented consecutively on the left or right side of the screen in alternating order.

The direction of each dog’s gaze on the images and pupil size were measured with a precise eye-tracking device. “We were among the first researchers in the world to use pupil measurements in the evaluation of dogs’ emotional states,” said Outi Vainion, DVM, PhD, a professor in the Department of Equine and Small Animal Medicine at the University of Helsinki and head of the research group. “This method had previously only been used on humans and apes.”

Dogs that received oxytocin were far more interested in smiling human faces than in threatening ones, which means oxytocin probably made the angry faces seem less threatening and the smiling faces more appealing. Without the hormone, they responded more emotionally to angry faces.

“Both effects promote dog—human communication and the development of affectionate relations,” said Professor Vainio.

Further studies are needed to determine whether the results are typical only for domestic dogs because of their regular interactions with humans, or whether a similar phenomenon exists in other species. And because the study dogs were presented with unfamiliar human faces, additional research is also needed to determine whether familiarity would affect the results.