The Chemical Bond Between Dogs and Their Humans

Written by Dr. Karen Shaw Becker

dog and human bond

Story at-a-glance -

  • A growing body of evidence provides ample scientific proof of the extraordinary bond between humans and dogs
  • Thanks to oxytocin and other feel-good hormones, humans and canines receive many physical and emotional benefits when we interact
  • Through the process of domestication, dogs have also learned to read human facial expressions and respond to our communicative intent

Scientists who specialize in studying all things canine are building an impressive body of research on the extraordinary bond between people and their dogs. Of course, those of us who share our lives with dogs reached the same conclusion long ago, but it's still nice to have our suspicions confirmed!

Indeed, studies prove there is true chemistry between dogs and their humans. Daily interactions with your canine companion have a measurably uplifting effect on your biochemistry, thanks to a hormone called oxytocin, sometimes called the "hug hormone" or the "love chemical."

Oxytocin is a naturally occurring substance in the body that makes skin-to-skin contact feel good. It also acts as a natural painkiller, and lowers stress levels and blood pressure.

It has long been established that human-to-human contact, for example, bonding with children or partners, triggers the release of oxytocin. More recently, studies have revealed that bonding with a completely different species also promotes release of this wonderful hormone.

When You Interact With Your Dog, Feel-Good Hormones Abound

In 2003, a study conducted at the University of Pretoria in South Africa revealed some fascinating insights about the interaction between dogs and their humans.1 Dog parents sat on a rug on the floor with their dogs and for 30 minutes, they focused solely on their pets. They talked softly to them, and stroked, scratched and petted them. The owners' blood was drawn at the beginning and again at the end of the 30-minute session.

The researchers found that the dog owners' blood pressure decreased, and they showed elevated levels not only of oxytocin, but also several other hormones. These included beta-endorphins, which are associated with both pain relief and euphoria; prolactin, which promotes bonding between parent and child; phenylethylamine, which is increased in people involved in romantic relationships; and dopamine, which heightens feelings of pleasure.

Interestingly, all the same hormones were also elevated in the dogs, which suggests the feelings of attachment are mutual. Next, the dog parents sat in the room and read a book for 30 minutes. None of the hormones, including oxytocin, increased as much as they did during the session with the dogs.

A decade ago, a Japanese study proved that when our dogs gaze at us, our oxytocin levels increase.2 The study involved 55 dogs and their owners. The people whose dogs gazed at them for two minutes or longer showed higher levels of oxytocin than owners whose dogs gazed at them for less time, and claimed to be happier with their dogs than owners whose dogs' gaze was only around a minute long.

In a 2011 Swedish study, researchers found that people who kissed their dogs frequently had higher levels of oxytocin than other owners.3 And along with kissing, there were two other factors that contributed to elevated levels of oxytocin. One was that the owners perceived their relationship with their dog to be pleasurable rather than difficult or a chore, and the other was that they offered fewer treats to their pet, preferring to offer attention and affection instead.

More Proof of the Bond We Share: Dogs Can Read Our Facial Expressions

Last year, a team of Italian researchers published a facial expression study involving 26 dogs.4 As the dogs ate, the scientists showed them photos of the same two human faces (a man and a woman). The pictures were deliberately positioned to the sides of the dogs' line of sight, and showed the humans intensely expressing one of six emotions — anger, fear, happiness, sadness, surprise or disgust. A second face displayed a neutral (non-emotional) expression.

The researchers observed that when the dogs saw facial expressions such as anger, fear and happiness, their heart rates accelerated and they tended to turn their heads to the left. They also took longer to resume eating than when they were shown the neutral face.

The scientists concluded the dogs were experiencing more stress while these three particular facial expressions were displayed, and theorized that the happy face caused stress because dogs instinctively view bared teeth as threatening. Interestingly, when the dogs were shown surprised facial expressions they remained relaxed and tended to turn their head to the right. They showed no "side bias" with their heads when shown pictures of sadness, disgust or a neutral expression.

These study results are further evidence of just how closely connected dogs are with people. According to the researchers, the dogs turning their heads either left or right also suggests our furry companions use different parts of their brains to process human emotions.

The right side of the brain plays a more important role in regulating the sympathetic outflow to the heart, and is fundamental in controlling the fight-or-flight response necessary for survival. Arousing, negative emotions seem to be processed by the right hemisphere of a dog's brain, and more positive emotions by the left hemisphere.

And Still More Proof: Dogs Respond to Our Communicative Intent

Research shows that dogs track human eye movements, and eye movements are linked with intent. A study published in 2012 in the journal Current Biology compared this ability in dogs to a similar one shown by human babies.5 For the study, 16 dogs were shown videos of a person turning toward one of two identical objects. In one video, the person looks directly at the dog and says in a lively voice, "Hi dog!" In the other video, the person avoided eye contact and said "Hi dog," in a low voice.

An eye tracker was used to capture the dogs' reactions, and researchers concluded from the data collected that the dogs were more likely to look at the object in the video featuring the more communicative person. This was the first study to use eye-tracking techniques to observe how dogs interact with people.

The study brought out an additional aspect of dogs' attentiveness to humans by demonstrating that when a dog's gaze follows a human, it's not simply a reflex. It's linked to the human's "communicative intent."

Even though your dog's brain doesn't process information the same way a human child's does, his ability to interact with you at this level helps strengthen the bond you share. And when you consider the biological differences between humans and canines, the fact that we're able to communicate back and forth is pretty remarkable!