The life of a domesticated dog may seem pretty relaxing: eat, play, bark, sleep, repeat. But it turns out, even dogs can’t escape the pressures of the human world.
Our canine friends may get sympathetically stressed out in response to their owners’ anxieties, according to a study in the journal Scientific Reports. Researchers in Sweden found that dogs’ anxiety levels rose along with those of their humans, implying that the pets are highly attuned to their human companions’ moods.
“Dogs are quite good at understanding humans,” senior author Lina Roth, a zoologist at Sweden’s Linkoping University, tells Carrie Arnold of National Geographic. “They’re definitely better at understanding us than we are at understanding them.”
Roth and her colleagues looked at 58 dog-owner duos: 33 Shetland sheepdogs and 25 border collies, and the owners were all human women. To measure just how stressed their participants were over a period of several months, the scientists analyzed hair and fur samples for concentrations of the stress hormone cortisol. While cortisol in the bloodstream can quickly spike and drop in “fight-or-flight” situations, consistently high levels of the hormone are associated with chronic stress—the kind of mental strain that comes with a more persistent problem, like unemployment or institutional racism. As hair grows, it accumulates cortisolcan serve as a chemical record of these long-term stress levels.
After measuring samples from two different time points to account for seasonal changes, the scientists found that when humans had high cortisol levels, their dogs did too. While earlier studies had shown examples of immediate “stress contagion” in high-pressure situations like competitions, authors write that this is the first evidence for long-term stress syncing between species.
The researchers also collected data about the personalities of humans and their pets using, respectively, the classic Big Five Inventory and the so-called Dog Personality Questionnaire—completed by the owner, of course. Interestingly, an owner’s personality seemed to have a stronger effect on their dog’s stress levels than the dog’s own traits, even though some pets were described as fearful or excitable.
The study is an exciting extension of earlier findings on the bond between humans and their canine companions, developmental psychologist Jonathan Santo—who has researched short-term emotional contagion but was not involved with this study—tells Melissa Healy of the Los Angeles Times.
“What this paper seems to hint at is some of the underlying mechanisms behind why humans and dogs or wolves have been able to domesticate each other over thousands of years,” Santo said. “We’re both social species, and once we became integrated into each other’s lives, it was to everyone’s advantage that dogs and humans would keep tabs on each other emotionally.”
For dog-human partners that trained together for agility competitions, the match in cortisol levels was even more accurate. This correlation could signal that such time-intensive activities bolster “emotional closeness,” Roth tells NPR’s Rebecca Hersher. Female dogs also mirrored their owners’ emotions more closely.
On the other hand, canine concerns didn’t seem to have as much of an effect on their humans: Stressed dogs didn’t always have similarly stressed owners, the authors found. The imbalance could stem from the lopsided nature of the pet-owner relationship, Roth says, as even the most doting of dog lovers have lives outside of their pets.
“We are quite a central part of their world,” Roth tells Healy. “We have work, and other circles of friends. But for a dog, we are almost everything.”
The study opens up several avenues for future research; Roth says she’s interested in replicating the experiment with different dog species beyond the collies and sheepdogs included in this research, which were already known to be friendly and responsive to their human companions. She also hopes to look more into how dogs’ and owners’ genders play into their emotional syncing.
The results don’t mean anxious humans should avoid adopting dogs for fear of stressing them out. Pet ownership is actually shown to benefit physical and mental health, as dog owners may live longer, have lower blood pressure and feel less anxious. Instead, Roth advises that dog owners simply be aware of how their moods could be affecting their pets, and make an effort to show them affection.
“If we just interact with the dog in a positive way, we do give the dog what it wants,” Roth tells Healy. “Have fun with your dog.”
In other words, the next time you come home grumpy, try giving your dog a belly rub—it could be good for the both of you.