Dog owners who suffer from high levels of stress could pass on their fretfulness to their pets, after a new study found that pressured people tend to own hassled hounds. Appearing in the journal Scientific Reports, the research provides yet more evidence for the ability of dogs to mirror the emotional states of humans.

Previous research has shown that levels of the stress hormone cortisol tend to become synchronized between competing dogs and their handlers during intense tournaments. However, since physical activity is known to affect cortisol levels, it is not possible to say whether this finding is the result of emotional harmony between dogs and people, or merely a product of exercising together.

To investigate, a team of scientists from Linköping University in Sweden recruited 25 border collies and 33 Shetland sheepdogs – all of whom were owned by women – and tested the cortisol levels in their hair at two intervals, several months apart.

"We found that the levels of long-term cortisol in the dog and its owner were synchronized, such that owners with high cortisol levels have dogs with high cortisol levels, while owners with low cortisol levels have dogs with low levels", said study author Ann-Sofie Sundman in a statement.

Because some of the dogs in the study were competing dogs while others were regular pets, the researchers also used a tracking collar to monitor their activity levels in the week leading up to each hair sample being taken.

Results showed that physical activity had no influence on the dogs’ long-term cortisol levels, which were always heavily linked to those of their owner.

The team also used a series of questionnaires to determine the personality traits of the canines and their masters, and found that the dogs’ character had no influence over their cortisol levels, but that owners’ personalities did.

In particular, dogs whose owners scored highly for neuroticism tended to exhibit lower levels of cortisol. The study authors speculate that this may be because neurotic owners rely heavily on their pets for comfort and support, creating a bond that provides an emotional crutch for both human and animal.

The researchers now plan to expand this investigation to include other breeds of dog, since both of the breeds used in this study are herding dogs, and have been selectively bred to pick up on their owners’ signals. It remains to be seen if other, less obedient dogs care quite so much about whether their owners have had a stressful day.