Do Hormones Determine Your Dog’s Temperament?

In this article:

• Why does a dog’s temperament matter, and how do we assess it?
• What did this study reveal?
• What do the results mean?
• What does this mean for training my own dog?

The doorbell rings. How does your dog respond?

An excitable dog may spring into action, barking as they sprint toward the door. One who’s calmer may barely bat an eye. The way your dog responds to stimuli like this can help reveal their temperament—a key part of their personality. 

Many factors contribute to a dog’s temperament, and new research suggests that hormonal fluctuations may be among them. Published in February in the journal PLOS One by researchers in South Korea, this paper found an association between specific hormone levels and temperament in 24 dogs. 

Why does a dog’s temperament matter, and how do we assess it?

All dogs deserve love and care, but temperament is an important factor when considering whether a dog is right for a specific home or job—and what kind of training and support they need. Dogs with particular dispositions may be better suited to certain tasks—calmer dogs, for example, often make good therapy animals. And when choosing a pet, people may have a certain temperament in mind—like when a family with young children seeks a mild-mannered dog.

The Wesen test is one tool used to evaluate canine temperament; it has played a role in selecting dogs for breeding and jobs as service animals. During the test, dogs encounter a series of stimuli, and receive scores based on their responses. The authors of this study used a version of the Wesen test to measure dogs’ temperament, and sought to find out how behavioral scores might relate to hormonal shifts.

“One thing that I love about this paper is the way it seeks to make a connection between behavioral research and research that occurs on a more hormonal level,” said Zachary Silver, PhD, an assistant professor of psychology at Occidental College, and founder and director of the school’s Canine Intelligence Lab. “That’s something that we don’t have a lot of in the field right now.” Dr. Silver was not involved in this research.

Hormones are chemicals that kick off various processes throughout the body in response to stimuli. Different hormones initiate different processes. These researchers studied two hormones in particular: cortisol and serotonin.

Dogs’ adrenal glands release cortisol in response to stress or negative emotional states (in addition to other stimuli). Serotonin—both a hormone and a neurotransmitter, or a chemical that delivers messages from neurons to all sorts of cells—helps regulate mood and serves other physiological functions.

Researchers have previously investigated the ways serotonin may affect dogs’ behavior; a 2012 paper comparing 28 aggressive dogs and 10 nonaggressive dogs found that on average, the aggressive dogs had significantly lower levels of serotonin in their blood than nonaggressive dogs.

What did the study reveal?

The authors used a version of the Wesen test to evaluate 24 dogs of different breeds. In this test, the researchers presented each dog with the same set of stimuli, including an unsteady walking surface, the sound of a car revving, strangers, an unknown dog, a hidden treat, and separation. They then evaluated the dogs for fear, relaxation, confidence, anxiety, and other qualities. Each dog received a score; lower scores reflected a more reactive temperament, while higher scores reflected a calmer temperament. The researchers then divided the dogs into three groups of eight indicating low, medium, and high scores.

Before and after the test, the researchers collected saliva samples from each dog. They analyzed these samples for cortisol and serotonin levels, using cortisol as a marker of stress—potentially driving reactive behavior—and serotonin as a marker of relaxation.

They found that dogs with higher scores had lower levels of cortisol before the assessment compared to dogs with lower scores. This could indicate that dogs with higher scores—that is, with calmer temperaments—may have a lower cortisol baseline, so when their cortisol levels increase in response to stress, they don’t have as dramatic a response compared to a dog with a higher baseline.

Conversely, dogs with lower scores—more reactive temperaments—also had higher levels of cortisol after the assessment compared to dogs with medium and higher scores. Taken together, these results suggest a link between a dog’s cortisol response and their overall temperament, but particularly how they handle stress.

As for serotonin, only 16 dogs’ salivary levels were analyzed. The researchers didn’t find any statistically significant correlation between overall temperament scores and serotonin concentrations, but within the unsteady-surface challenge in particular, high-scoring dogs had higher serotonin levels. Dogs with higher scores also had much higher pre-assessment levels of serotonin than dogs with lower scores.

What do the results mean?

None of this is to say that high-scoring dogs are good and low-scoring dogs are bad. (All dogs are good; you don’t need a PhD to know that.) The paper’s findings simply suggest that dogs’ temperament may, in part, be determined by hormones.

“I think this research tells us that a dog’s temperament is something that is biological in nature,” Dr. Silver said. While some dog owners may believe they can train a dog to do (or not do) anything, “temperament is a hard thing to adjust,” he said. Training methods like desensitization and counterconditioning can help shape a reactive dog’s behavior—and improve their quality of life. But, depending on a dog’s temperament, they can only do so much. That’s why, Dr. Silver added, it’s important to extend grace to ourselves—and to the dog, who is doing their best—if training seems difficult.

Still, this paper has its limitations. Brian Hare, PhD, a professor of evolutionary anthropology at Duke University who was not involved in this study, is skeptical of using salivary cortisol to measure stress. He pointed to a 2025 paper he co-authored that found cortisol levels in saliva poorly correlated with blood cortisol levels in puppies.

Dr. Silver acknowledged that salivary cortisol has its shortcomings as a stress indicator, but still saw value in measuring it. “Even though the measures are not perfect, they’re still effective,” he said.

The study was also small. Other researchers want to see this research replicated with more dogs. While the 24 studied here were “enough to potentially find an association—and they did seem to find one—it would be nice to see this hold up with a larger sample of dogs,” said Kyle Smith, PhD, a postdoctoral researcher studying dog cognition at North Carolina State University, who was not involved in this study.

Dr. Silver also mentioned that there are various ways to define temperament. For him, repeating this study while looking at other measures of disposition could reinforce the idea that there is a relationship between a dog’s hormones and temperament.

How can this help me train my own dog?

Zazie Todd, PhD, the psychologist and certified dog trainer who wrote Bark! The Science of Helping Your Anxious, Fearful, or Reactive Dog, broke down the factors informing temperament into what we can’t change (like genetics and early life experiences) and what we can change (like environment and training). 

Training can succeed at moderating reactive behavior. “There are no guarantees, but most of the time training can make a big difference to reactivity,” she said.

She recommended rewards-based methods for the best results in the long run. Sometimes dogs are reactive because they’re scared, for which the best approach is desensitization and counterconditioning, or changing the environment to help them feel safer. “The sooner you take action, the faster it will work,” she said.

And, while training can and does affect a dog’s behavior, this research underscores that biology is also an important factor shaping who they are. “If we want to correct problematic behaviors, think not about changing a dog’s overall temperament—but instead think about addressing those specific contexts,” Dr. Silver said, making reference to the benefits of using management in conjunction with training. “We just have to try to create situations where we are giving the dog the best possible chance to succeed.”