Is long-term stress contagious between species?

Dogs and humans have lived closely together for at least 15,000 years and various studies have been undertaken to explore their unique bond.

These studies have shown that short-term stress appears to be contagious between the species but, to the author’s knowledge, this is the first time that long-term stress interspecific synchronization hypothesis is explored.

Based on the premise that serum cortisol is gradually incorporated into hair as it grows and that it can thus help us to create a retrospective calendar of the hormone ‘s concentration, the hair cortisol concentrations (HCC) of both owners and dogs were examined in this study.

58 human-dog dyads HCC were evaluated once during Summer and once during Winter. The personality traits of the individuals were also assessed via surveys and the activity level of each dog was monitored.

The study included male and female dogs from two breeds – the Shetland sheepdog and Border Collie.  Some were working dogs and others were pets to ensure that differing lifestyles were incorporated.

The results show a clear synchronization between dogs and their owners: when there was an increase in the HCC level in humans, it was mirrored in their dogs. But it did not work the other way round.  The effect was stronger in the working dyads and in females, which also showed higher basal levels of cortisol. Explanations for these results are described in this interesting article that reiterates the importance of human-dog interaction from a welfare perspective for both species.

Sundman, A., Van Poucke, E., Svensson Holm, A. et al. Long-term stress levels are synchronized in dogs and their owners. Sci Rep 9, 7391 (2019). https://doi.org/10.1038/s41598-019-43851-x