When dog owners experience a long period of stress, they are not alone in feeling the pressure. Their dogs feel it, too.

That information comes from new a study published Thursday in Scientific Reports.

Swedish scientists centered the research on 58 people who own border collies or Shetland sheepdogs. Both are traditionally herding dogs.

The scientists examined hair from the dog owners and their dogs. They looked at the levels of a hormone called cortisol. This chemical is released into the bloodstream during stressful experiences. Pieces of hair can take in this chemical.

Depression, extreme physical exercise and unemployment are just a few examples of stress causers that can affect the amount of cortisol released in humans, said Lina Roth of Sweden's Linkoping University.

Roth and her team found that cortisol levels in the hair of dog owners closely matched levels found in their dogs. The researchers say this suggests their stress levels were in sync -- or connected.

Roth believes that the owners are influencing the dogs instead of dogs influencing their human owners. That is because there are human personality traits that also appear to affect dogs' cortisol levels.

But, why is it that people influence their dogs and not the other way around? It could be, Roth said in an email, because people are "a more central part of the dog's life, whereas we humans also have other social networks."

The study results are no surprise, said Alicia Buttner. She is director of animal behavior with the Nebraska Humane Society in the American city of Omaha.

Buttner said new evidence is continually found to show people and their dogs have extremely "close bonds that resemble the ones that parents share with their children."

Buttner also said there is not enough evidence to prove that the influence goes only one way.

She said, "It's not just as simple as owner gets stressed, dog gets stressed."

Buttner said cortisol levels do not necessarily demonstrate "bad" stress. They instead can be representative of a good experience like getting ready to go for a walk, she said.

Roth and her team plan to investigate whether other kinds of dogs react to their owners the same way.

For now, she offers advice for reducing how much stress a dog owner may be causing their pet. Dogs that play more show fewer signs of stress, she said.

So "just be with your dog and have fun," Roth said.

I'm Ashley Thompson

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stress - n. a state of mental tension and worry caused by problems in your life, work, etc.

match - v. to be the equal of (something or someone)

trait - n. a quality that makes one person or thing different from another

resemble - v. to look or be like (someone or something)