Your stress is likely stressing your dog out, new study finds

When our dogs come running up to us with a wagging tail, even the worst of days brighten up. And when our dogs are sick, we worry and hurt, too.

But how often do we think about the effects of our stress on our four-legged friends? A new study suggests that when owners go through periods of long-term stress, their dogs mirror those stress levels.

The dog's personality was not a factor, the study showed, but the owner's personality had "extensive impact on dog HCC (hair cortisol concentrations)". This led the researchers to believe that dogs mirror owners' stress levels, and not the other way around.

The study, authored by researchers at Linköping University, examined the concentration of cortisol, a stress hormone, in a few centimeters of hair from 33 Shetland sheepdogs, 25 border collies and their respective human owners. Cortisol is stored in hair as it grows in proportion to the amount of cortisol in blood. This enabled the researchers to study the stress levels of both canines and humans over months before a sample is taken.

The researchers discovered that there was a correlation between the level of stress in a dog and its owner. With an increase in human HCC, there was an increase in canine HCC.

The study examined both pet dogs, which tend to be less active, and active competition dogs, which usually engage in physical exercise with their owners.

Researchers found that the stress level of competing dogs correlated more strongly with that of their owner, which scientists believe may be associated with the higher degree of interaction between the human and the dog.

"It may be that competing owners and their dogs spend more time together engaging in the same tasks," the study reported. "Indeed, training may increase emotional closeness... and thereby generate a stronger synchronization."

This study came from previous work that showed how individuals of the same species can mirror each others' emotional states, including long-term stress correlations between infant children and their mothers. The researchers believe the study to be the first to show interspecies synchronization of long-term stress.