The Swedish researchers focused on 58 people who own border collies or Shetland sheepdogs. They examined hair from the dog owners and their dogs, looking at the concentrations of a hormone called cortisol, a chemical 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, said Lina Roth of Linkoping University in Sweden.

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