Dog owners experiencing long bouts of stress can transfer it to their dogs, scientists report in a study published Thursday in Scientific Reports.

A group of Swedish researchers focused on 58 people who own border collies or Shetland sheepdogs. They examined hair from the dog owners and their dogs. The scientists were looking at the concentrations of a hormone called cortisol. This chemical is released into the bloodstream and absorbed by hair follicles in response to stress.

Depression, excessive physical exercise, and unemployment are just a few examples of stress that can influence the amount of cortisol found in your hair, says Lina Roth of Sweden’s Linkoping University.

Roth and her team found that the patterns of cortisol levels in the hair of dog owners closely matched that found in their dogs. The pattern held in both winter and summer months, indicating their stress levels were in sync.

She thinks the owners are influencing the dogs rather than dogs influencing owners.

The researchers don’t know what causes the synchronization in cortisol levels between humans and their pups. But the link is stronger with competitive dogs than in pet pooches. That may provide a hint.

The bond formed between owner and competitive dogs during training may increase the canines’ emotional reliance on their owners, Roth says. That in turn could increase the degree of synchronization.

But why do people influence their dogs rather than vice versa?  Perhaps people are “a more central part of the dog’s life, whereas we humans also have other social networks,” Roth suggested. People go to work, church, school. They invite friends over and go out with others. But dogs get to do social things only when the owner initiates it.

Alicia Buttner wasn’t surprised by the study results. She is director of animal behavior with the Nebraska Humane Society in Omaha. She is not sure the influence goes only one way, however.

“It’s not just as simple as owner gets stressed, dog gets stressed,” Buttner says. Many other factors can affect a person or dog’s stress levels—increasing or dampening them. Buttner also reminds that an increase in cortisol isn’t necessarily a sign of “bad” stress. The body can release cortisol in people or dogs when a good and exciting event is about to take place—like a wedding, or “walkies!”—depending on your perspective.

More study will be done to investigate whether other dog breeds react to their owners like the collies and Shetlands did.

But in the meantime, Roth has some advice to reduce stress: “Just be with your dog and have fun.”

(A Shetland sheepdog at the Westminster Kennel Club Dog Show in February pays close attention to its handler. A study published on June 6, 2019, suggests that dog owners experiencing long bouts of stress can transfer that stress to their dogs. AP Photo)