Your Dog Is Your Mirror

1 Swedish study: stress in 58 dogs and their owners

One study · 58 dogs of two herding breeds · owners all women · Sweden (Sundman et al., 2019).

There is an old saying: if you want to know a person, look at their dog. In 2019, researchers at Linköping University in Sweden tested a version of it with something that cannot put on an act.

They studied 58 dogs and their owners. Instead of asking anyone how stressed they felt, they took a small sample of hair from each dog and each owner and measured cortisol, a stress hormone. As hair grows, cortisol from the blood is built into it, so a sample works like a calendar of the months before. They did it twice: once for the summer months, once for the winter months.

The result held in both seasons: the long-term stress levels of dogs and their owners were synchronized. Owners with higher cortisol had dogs with higher cortisol; owners with lower levels had dogs with lower levels. According to the researchers, it was the first time long-term stress had been shown to synchronize between two species.

In these two herding breeds, that is what makes the old saying more than a saying. A dog does not act or pretend — and neither does his hair. A feeling can be misjudged or tidied up afterwards. Months of a hormone laid down in hair cannot.

2 Your personality and his: which one is linked to his stress?

The researchers also looked for other explanations. Each owner filled in a personality questionnaire about herself and one about her dog, and every dog wore an activity tracker for a week.

• The dog’s own personality had little effect on his long-term cortisol.
• The owner’s personality did. Three of the five traits measured — neuroticism, conscientiousness and openness — were significantly linked to the dog’s level.
• How active the dog was made no difference, and neither did how many training sessions he had each week.

But not in the direction you might expect. Owners who scored higher on neuroticism — being prone to worry — had dogs with lower cortisol, in both seasons. Owners who scored higher on conscientiousness and openness had dogs with higher cortisol in winter. The researchers’ suggestion for the first result: people who score high on neuroticism may form a strong bond with their dog, leaning on him for support and supporting him in return. This is not a ranking of good and bad owners.

A study like this finds a link, and on its own it cannot prove which way the link runs. Still, because the owner’s traits, not the dog’s, were linked to the dog’s cortisol, the researchers suggest that dogs, to a great extent, mirror the stress level of their owners.

3 Does this apply to Frenchies too?

Before any of this is applied to a Frenchie, it is worth seeing exactly who was in the study.

The same research group went on to check other dogs. The 2021 study (Höglin et al.) included 24 ancient-breed dogs and 18 hunting dogs, chosen to work independently of people, and their owners. In them, no link was found between the owner’s cortisol and the dog’s. The authors conclude that synchronized stress is probably a trait of breeds selected for cooperation with people. In the hunting dogs, cortisol was linked to the owner’s personality, but not to the owner’s cortisol. It was a small study, and the owners volunteered.

A Polish study from 2022 (Wojtaś et al.) did not find a link either: 25 households with women owners, 45 dogs and 55 cats, one hair sample each. Overall there was no relationship between the owner’s cortisol and her dog’s. In a few subgroups there was (for example, dogs whose owner groomed them once a week), but those are parts of an already small study and should not be generalized.

So the “mirror” has been found in two herding breeds, and not in other dogs. There were no Frenchies in the Swedish studies, and the Polish study does not say which breeds took part, so we do not know whether it shows in a Frenchie.

4 Japanese study: the longer owner and dog live together, the more in step their hearts beat

The Swedish study shows that the two stress levels go together, not how. The researchers place it within emotional contagion — the mirroring of emotional or arousal states between individuals.

A small study in Japan (Katayama et al., 2019): 34 pairs took part and 14 made it into the final analysis, so read it as a direction, not a rule. The researchers recorded the heartbeats of dogs and their owners, with the dog in the room, on two separate days: once while the owner read quietly, and once while the owner went through a stressful test of public speaking and mental arithmetic. The longer a dog and owner had lived together, the more closely their heart rhythms moved together — on the calm day and on the stressful one. The authors conclude that emotional contagion can pass from owner to dog, and that time shared makes it stronger.

It points the same way as another detail of the Swedish study: there, the link was stronger in dogs that trained and competed with their owners in agility or obedience, and the researchers speculate that the extra time spent working together may explain it. The more life a dog and his person share, the closer the link seems to be.

5 Does where you live affect your dog? Studies from the US, Hungary and Finland

A dog does not only live with his owner. He lives in a house, a street, a climate and a way of keeping dogs — and none of that is the same everywhere.

A 2009 study (Wan et al.) compared German Shepherds in the USA and in Hungary, through questionnaires from owners in breed and obedience clubs — 51 owners in the USA, 185 in Hungary. Owners in the USA were far more likely to keep their dogs indoors by day and at night, to call them pets or family members, and to train them in more kinds of activities. Hungarian dogs lived outdoors more often, yet the study found no real difference in how much time they spent with their owners each day. And owners in the USA rated their German Shepherds as more confident and more aggressive than owners in Hungary rated theirs.

The researchers give two possible readings. The dogs may truly differ — for example, if breeders in one country choose more confident dogs. Or owners in the two countries may simply have a different idea of how a German Shepherd should be, and rate the same behavior differently. Only watching the dogs themselves could settle it. Their conclusion is the part worth keeping: a finding from dogs in one country should not be assumed to hold for all dogs.

Place matters inside one country too. In Finland, an owner survey of about 6,000 dogs (Puurunen et al., 2020) found that dogs living in more urban surroundings were more often afraid of strangers and of other dogs.

That is why this page says where each study was done: the stress study in Sweden, the heartbeat study in Japan. Dogs live very different days — in an apartment, or in a yard behind a gate onto a busy street, around free-roaming dogs. Read the findings, then look at your own place.

6 What this means for you: information, not blame

A finding like this is easy to turn into guilt. That would be the wrong way to read it.

• It is not a verdict on you. The study found that two stress levels go together. It did not show that owners cause their dogs’ stress — and a link can run the other way too: living with a dog who struggles is stressful as well.
• Other causes are real. Genes, being separated from the litter too early, pain and fear of noises all shape how a dog copes — and a calmer owner does not undo them.
• A sudden change is a question for the vet. Pain and illness can change behavior, and they come before anything on this page.
• You will probably never see it happen. This was measured in hair, over months. An owner who lives with a dog every day may never catch a single moment of it — which is why it took a laboratory to find it.

What it does mean is simpler, and it is good news. You are part of your dog’s world, so you are also part of what can help him. Looking after yourself is one of the ways you look after him.

So do not look for the moment. Look at the whole picture instead: what he fears, what he guards, when his body tightens. Then look at the days you share — to understand him, not to find someone to blame.

In any case, it is always good to work on yourself, on your emotions and on your well-being.

7 Spike: our experience

Our stories and opinions on this page are our personal experience with one dog, Spike. One dog is not the measure for every dog — for your dog, your vet decides.

Spike’s reality  ·  Dominican Republic

“At home he barks if he hears something, but there are no special reactions.”

We looked for a moment when you could see Spike pick up on our mood. In almost eight years of living with him, we could not find one.

The only thing we notice is that he protests when the car leaves without him — and that is about missing the ride, not about anyone’s mood.

That does not contradict the study. What the researchers measured built up in hair over months. It is not something that happens in front of you.

Our opinion: this may not be a rule, but sometimes it seems to us that a dog is linked to his person by more than hormones, and that he literally imitates him in some things: if the person is aggressive, the dog is aggressive, and if the person is calm, the dog is calm. A dog looks more like his person than we usually think.

About the Author

Spike’s Dad

Not a veterinarian — the human behind Spike, a dark brindle Frenchie, for 7+ years. What is written here is checked as carefully as we can against the sources listed above. When real life with Spike differs from the studies, we say so.

How this site is researched →