The Chemistry of a Very Good Boy: Can a Simple Saliva Test Predict a Dog’s Personality?

Your dog’s saliva might reveal if they are destined for police work or the couch.

Assessing a dog’s temperament can be a high-stakes game. Get it wrong in a police dog, and you have a dangerous liability. Get it wrong in a family pet, and you may end up with a heartbreaking return to the shelter. Scientists and dog trainers alike have traditionally relied on behavioral checklists to grade dogs, but these tests suffer from a classic flaw: they rely on human observers, who are notoriously subjective.

Now, researchers are suggesting we bypass the human element entirely and go straight to the source code: the dog’s biology. A new study published today in PLOS One suggests that the difference between an overly anxious pup and a rock-solid working dog might be detectable in a few drops of saliva.

Beyond Dog “Vibes”

The current gold standard for judging canine character involves tests like the “Wesen test” (German for “character” or “nature”). It’s a behavioral obstacle course designed to rattle a dog to see if or when they shake. A judge watches the animal react to strangers, loud noises, and unstable surfaces, then assigns a score.

While useful, this method is not completely reliable due to the human element. One judge’s “cautious” is another judge’s “fearful.”

Minjung Yoon and colleagues at Kyungpook National University in South Korea wanted to see if they could anchor these subjective scores to hard biological data. They recruited twenty-four dogs — a mix of breeds including Border Collies, Malinois, and six Beagles bred specifically for experimental use — and put them through a modified version of the Wesen test.

This time, the researchers weren’t just watching the dogs, they were also swabbing their cheeks. They measured levels of two key chemicals before and after the test: cortisol, the infamous “stress hormone,” and serotonin, often dubbed the “happiness hormone.”

Stress, Saliva, and Stability

The test itself was no walk in the park. To measure “Noise Stability,” dogs were exposed to the sounds of a motor, a metal chain, and a cracking whip. To test their nerve on physical terrain, they had to walk across an unstable pallet and navigate connected tables. In a particularly rude surprise called “Behavior in Stressful Situations,” a metal chain was dropped suddenly while the dog was searching for a toy.

When the researchers compared the chemical data to the behavioral scores, a clear pattern emerged. The dogs that aced the test by showing confidence, stability, and friendliness had significantly lower levels of cortisol in their saliva before the test even began.

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Perhaps more telling was how they handled the pressure. The low-scoring dogs didn’t just start with more stress; their bodies flooded with cortisol during the test. The high-scoring dogs maintained a chemical cool, showing a much less dramatic spike in stress hormones.

It suggests that what we call “temperament” is biologically regulated by the hypothalamic-pituitary-adrenal (HPA) axis. This is the biological feedback loop that manages homeostasis. In “good” dogs, this system seems to resist hitting the panic button, keeping them chemically calm even when a metal chain crashes to the floor next to them.

The Serotonin Factor

While cortisol tells us about stress, serotonin mainly regulates stability. Serotonin is a neurotransmitter that regulates mood, and in humans, low levels are linked to depression and anxiety. It turns out, the same logic applies to our four-legged friends.

The study found a significant split in serotonin levels between the top performers and the bottom tier. Dogs that scored high on the Wesen test had significantly higher baseline levels of serotonin compared to the low-scoring group.

The authors note that “prior research has linked lower levels of cortisol, and higher levels of serotonin, with less aggressive behavior in dogs”.

Essentially, a dog with a brain awash in serotonin might be naturally inoculated against the kind of fear and aggression that makes for a bad pet or a failed working dog. The chemical data backs up the behavioral observation: happy dogs are stable dogs.

From Lab to Leash

It is important to note that this was a small pilot study. With only 24 dogs, we can’t make sweeping generalizations about all canine kind. However, the diversity of the group — ranging from purpose-bred lab Beagles to privately owned pets — adds an interesting layer to the data. It hints that these biomarkers might hold true across different upbringings and genetic backgrounds.

Currently, training a service dog can cost tens of thousands of dollars in the U.S., and many wash out halfway through the program. If a simple saliva swab could flag a dog as chemically prone to anxiety before training begins, it could save immense resources.

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As the authors conclude, “Our study shows that physiological concentrations of hormones and neurotransmitters can serve as biomarkers of canine temperament. These results could help identify dogs suited for specific working roles — such as military, police, guide, or therapy dogs — and assist in making better-informed companion dog adoption decisions”.

We aren’t quite at the point where you can take a 23andMe-style spit test to find your perfect puppy soulmate. But we are getting closer to understanding that a “good boy” isn’t just a matter of training or luck, it’s also a matter of chemistry.