• References

    References

    Parr-Cortes Z et al. (2024). The odour of an unfamiliar stressed or relaxed person affects dogs' responses to a cognitive bias test. Sci Rep 14, 15843.

    Wilson C et al. (2022). Dogs can discriminate between human baseline and psychological stress condition odours. PLoS One 17, e0274143.

Man’s Stressed Friend: How Human Stress Affects Dogs

16 January, 2025;
Man’s Stressed Friend: How Human Stress Affects Dogs

It may come as no surprise that dogs are the most common pets worldwide, with around a third of all households owning at least one. You’ve probably also heard about the benefits of dogs on the physical and psychological state of humans. For example, petting a dog has been shown to significantly reduce cortisol and increase oxytocin, leading to reductions in stress, lowered blood pressure, and overall benefits to cardiac health.

But did you know that our emotional state can also impact the mood of our furry companions? In this blog, we discuss a recent paper by Parr-Cortes et al. (2024) which investigates how human stress affects the emotional state of dogs.

Trick or Treat

The researchers set out to investigate a phenomenon known as “emotional contagion”, which describes the perception and mimicry of emotions between individuals in a group.

We know from previous studies that dogs are able to identify stress odors when sniffing samples of breath and sweat from stressed or relaxed humans (Wilson et al. 2022). However, whether detecting human stress can trigger an emotional response in the dog had yet to be studied.

But how exactly can we determine the emotional state of animals that can’t vocalize their feelings to us? Well, Parr-Cortes et al. used a clever experimental setup involving one thing that is sure to cause an emotional response in a dog ­— treats!

In this setup, a food bowl was placed in one of five doors in a screen located 3.5 m in front of the animal (Figure 1). First, a training phase was performed in which only the two doors on the furthest sides of the screen were utilized. A food bowl in door one always contained a treat (positive or P), while a food bowl passed through door five never contained a treat (negative or N).

Once the dogs had become accustomed to this pattern, the scientists began to pass a food bowl through one of the middle three doors instead — door two (near-positive or NP), door three (middle or M), and door four (near-negative or NN). These were labeled as “ambiguous locations” as the dog had no learned associations with these doors.

This type of cognitive bias testing can assess the emotional state of an animal, with negative emotional states causing an animal to make more pessimistic judgments about an ambiguous outcome (i.e. assuming a lack of treat), whereas animals with positive emotional states are more likely to make optimistic judgments (i.e. assuming the presence of a treat). Thus, the likelihood of the dog approaching the mysterious middle food bowls is related to their emotional state.

Fig. 1. Setup of the cognitive bias testing. P, positive; NP, near-positive; M, middle; NN, near-negative; N, negative. Adapted from Parr-Cortes et al. (2024).

Don’t Sweat It

To assess how human stress affected the dogs’ emotional state, the participating pups were exposed to cloths containing either stressed or relaxed human odor prior to each testing round. Before we dive into the results of this study, let’s take a little detour and have a look at how these sample odors were obtained.

Prior to the experiment, healthy volunteers were recruited to take part in a stress test. They attended two 1-hour long sessions, the first of which contained a 20 minute stress test, whereas in the second they watched 20 minutes of video compilations of forest and seaside clips to induce relaxation.

Each session started with the participant rinsing their armpits and mouth with water, and having a heart monitor attached, before sitting quietly in a waiting room for 10 minutes. After this, a pre-test saliva sample was collected, an anxiety questionnaire was completed, and collection cloths were attached to their armpits. At this point, the volunteer was called into the testing room for their stress test or relaxing activity. Then, a post-test saliva sample and anxiety questionnaire were collected, odor cloths were removed, and a breath sample was also collected onto the same cloth.

You may be wondering what exactly could cause an intense enough stress response consistently throughout the participants in only 20 minutes. The answer is clear: public speaking and math.

Upon entering the testing room, the participant was unexpectedly introduced to a public speaking expert and told they had 10 minutes to prepare a 5 minute speech on why they would be a good fit for their dream job (with the timer visible to them at all times), which would be videoed and they would be assessed on their performance. During their speech, if the participant stopped talking before the 5 minutes were up they were prompted to keep going, and the assessors maintained a serious expression at all times.

Sounds like a nightmare, right? But it doesn’t stop there. After the speech task, participants were instructed to do some mental math for 5 minutes, stating their answers aloud. Starting with the number 1,022, they were asked to continually subtract 13, and if they made a mistake, they were told it was incorrect and had to start again.

If that’s not enough to get your heart racing, I don’t know what is!

No Risk, No Reward

So, with sweat-filled cloths in hand, the researchers undertook their experiment, exposing the dogs to either the relaxed or the stressed human odor before treat testing.

They found that the dogs were roughly half as likely to approach the food bowl at the NN location when the smell of human stress was present as compared to the absence of stress odors. The results suggest that dogs have a more pessimistic approach to ambiguity and decreased expectations when in the presence of a stressed human’s scent. A negative emotional state typically causes risk aversion, which is hypothesized to be an attempt to conserve energy and avoid disappointment if the individual believes the reward to be unlikely.

Therefore, this study suggests that you should take a break from this dog-eat-dog world and relax for the good of your pet’s mental wellbeing. So, next time you’re feeling under pressure, why not obey the usual commands you give your pup: sit on the sofa and put your feet up, stay there for an extended period of time, and when it comes to overthinking stressful situations, just drop it!

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References

References

Parr-Cortes Z et al. (2024). The odour of an unfamiliar stressed or relaxed person affects dogs' responses to a cognitive bias test. Sci Rep 14, 15843.

Wilson C et al. (2022). Dogs can discriminate between human baseline and psychological stress condition odours. PLoS One 17, e0274143.

 

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