You’ve likely heard of drug-sniffing dogs. And bomb-sniffing dogs. But stress-sniffing dogs? Well, they now exist, thanks to researchers who have taught dogs to detect signs of people under psychological stress. 

Dogs have superior sniffing skills, as we all know. Researchers refer to it as the “canine olfactory system.” It’s been used for other medical purposes, including diabetes alerts when there are changes in a person’s blood sugar levels and lung cancer detected based on breath samples. Well, when we’re stressed, our body has various physiological changes, from cortisol being released in the bloodstream to increased heart rate, blood pressure, and respiration. So, guess it shouldn’t be too surprising that dogs can pick up on that, too.

Who discovered this?

It was researchers at Queen’s University Belfast and Newcastle University in the U.K. who wanted to know if it was possible. They wondered if the physiological changes would cause the scent of sweat and breath odor in a stressed person to be different from that person when they’re not stressed. And if they were different, could a dog detect the change? Their finding showed it was, and is, possible, with an accuracy of 93.75%! The dogs were very reliable at picking out samples of breath and sweat taken from an individual experiencing psychological stress. 

Their results are published in a peer-reviewed journal, PLOS ONE. The researchers said they were fascinated watching the dogs discriminate between the smell samples, given the only difference was that there had been a psychological stress response. 

How did they do it?

dog nose

The researchers recruited pet dogs from the Belfast area of Ireland for the study. They originally selected 20 dogs, then eliminated a few from the study for a variety of reasons throughout training. In the end, four dogs completed the training. 

Those dogs included the following:

  • Male Cocker Spaniel
  • Female Cockapoo
  • Male Mixed Breed
  • Female Mixed Breed

The youngest was 11 months old, and the oldest was three years. They were trained to repeat behaviors with desired consequences and rewarded with positive reinforcement.

The study started in December 2019 and was forced to stop during the pandemic. It picked back up again, and in total, the extensive training lasted about an hour each week for 10 months.

They used a special device in the study; it had a base with three aluminum arms, and each had a cylinder-shaped port with a removable lid. The dogs were taught to sit or stand in front of this device with their nose touching it for five seconds. Then, researchers put sweat samples taken from volunteers on gauze and a piece of food inside one of the ports. They put unused gauze in the other ports. 

Once a dog successfully chose the port containing food, the researcher used a clicker and gave a food reward. After identifying it correctly on eight of ten attempts, the food was removed. 

The dogs were then given three ports with no food inside. One port had a human sweat and breath sample, but the other two had blank samples. Once the dogs could pick the port with the sweat/breath sample seven out of ten times, they moved to the next phase.

For the next phase, the ports were filled with a piece of gauze containing sweat and breath from the same person from the earlier challenge (target), a sample from a new person, and a blank. Dogs had to pick the target 16 out of 20 times for two consecutive terms to move to the next training phase. 

In the next phase, the dogs were presented with breath samples taken from the same person at two different times of the day. The sample used in the morning was typically the target sample, and once the dogs succeeded in this challenge, they went to the testing phase.

How did they create the stress?

Math is hard - mind full of numbers

Researchers recruited 53 people to take part. Forty did so in person, and 13 did it remotely because of the pandemic. They had to be non-smokers and agree not to eat anything flavored for at least an hour before giving their breath sample. They also had to refrain from mood-altering drugs for at least an hour before the sample was taken.

A piece of gauze was wiped on their necks and then placed in a vial. They then exhaled into the vial three times and secured it. After that, they completed a self-report on their current stress level. 

Then, they completed a mental arithmetic task counting out loud backward from 9,000 in units of 17 without using a pen or paper (yep, this would stress me out a bit, too). Researchers were stern about ordering them to continue until told to stop. If they answered correctly, they got no feedback and had to continue. If they were wrong, the researchers said no and then gave the last correct answer. This went on for three minutes. 

After this drill, a piece of gauze was again wiped on their necks and placed in a vial. Then they exhaled into the vial three times, just as before. They did it again with a second vial and completed another self-report questionnaire on their stress.

At the same time, researchers monitored their heart rates and blood pressure. 

If the self-report indicated an increase in stress by at least two points, along with an increase in heart rate and blood pressure (for in-person participants), their samples were used for the test with the dogs. The testing with dogs happened within three hours of these drills.

Eleven participants were excluded for not showing enough stress response. Five others were excluded for other reasons, which left 36 participants’ samples to be tested. 

Next steps

Stressed woman at her desk

During the first phase, one port was filled with a sample of sweat and breath from a stressed participant, and the other two were filled with blank samples. 

The next phase had a port with one stressed sample, another with a piece before the stress test, and a blank sample.

The dogs underwent this round of testing with 10 phase-one and 20 phase-two trials, with researchers focusing on the phase where dogs discriminated between the stressed and baseline samples.

The dogs’ detection rate for stressed samples was nearly 94% on average. 

So what’s next?

Other researchers say they’re not surprised by the findings. A dog’s great sense of odor can be used for a number of medical purposes, so there’s a great deal of promise in using it for stress awareness, too. The researchers believe their test results add to our understanding of human-dog relationships and could have applications for service dogs that help with Emotional Support and Post Traumatic Stress Disorder (PTSD). Chronic and/or acute stress can have a huge impact on your health, so having an animal be able to detect this stress – and potentially even lessen it – could make a life-changing difference.

No matter where this research leads, most pet owners will tell you that having a dog around can undoubtedly take away some of your stress. Training them to detect them would be a total bonus!

Read Next:

Beating Caregiver Stress and Burnout: Why You Need a Caregiver Support Group

Stress Test: What it Can’t Tell You

Steps You Can Take Now to Manage Stress


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