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Many people work stressful jobs but at least some get to come back home to a loving canine. However, according to a new study, we might want to be more careful with our mood in front of our beloved pets. The study found that dogs can not only feel that we are stressed, but it also causes them to feel stressed. The researchers say that this is the first time we’ve seen a long-term synchronization in stress levels between two different species.

The study was performed by Swedish researchers at Linköping University who recruited 25 border collies, 33 Shetland sheepdogs, and their human female owners. In order to measure stress in both dogs and humans, the researchers used markers found in strands of hair. Cortisol, the stress hormone, accumulates over time in growing hair, so each shaft becomes a biological record of stress — not all that different from measuring droughts in tree rings or temperature in ice cores.

Researchers focused on shorter strands of hair that corresponded to growth in the winter and summer of 2017 and 2018. They found that human and dog cortisol levels closely matched and held through the seasons, although dogs felt slightly more stressed during the winter.

Half of the dogs were enrolled in regular training and competitions, while the other half were regular pets. Competing dogs more closely mirrored the stress levels of their owners, presumably because the owners and their pets formed stronger bonds.

Remarkably, whether the dog had a garden to play in, the number of hours an owner worked, and whether the dog lived with other canines had little influence on cortisol level. This means that the environment has less influence on a dog’s stress than the owners themselves. Female dogs showed a higher cortisol concentration than male dogs. Previous studies showed that in most species, females show a higher emotional responsivity, which may explain the stronger association for cortisol levels between human owners and female dogs.

Owners who had a high score for neuroticism — a personality trait involving a long-term tendency to be in a negative or anxious emotional state — had dogs with the lowest hair cortisol levels. This may be explained by the fact that neurotic owners might seek more comfort from their pets, thereby giving them more attention, hugs, and treats.

For many dog owners, these findings shouldn’t come as a shocking surprise. Dogs are known to be highly affected by the owners’ moods, especially the crummy kind. And at the end of the day, you shouldn’t feel too guilty either. The researchers say that it’s still better for you and your dog to stay together even if you pass on the stress.

“Our results show that long-term stress hormone levels were synchronized between dogs and humans, two different species sharing everyday life. This could not be explained by either physical activity or by the amount of training. Since the personality of the owners was significantly related to the HCC of their dogs, we suggest that it is the dogs that mirror the stress levels of their owners rather than the owners responding to the stress in their dogs. To our knowledge, this is the first study to show interspecies synchronization of long-term stress,” the authors concluded in the journal Scientific Reports