t is easy for your dog to know if you're stressed, and that's because it may smell it in your breath and sweat, according to a new study.

Previous studies have suggested that dogs can tell if people are stressed, a team of researchers wrote in their study, published Wednesday in PLOS (Public Library of Science) ONE. Since dogs are known to have an incredible sense of smell, the researchers sought to find whether may actually be sensing the stress through chemical signals, PLOS noted in a news release.

So for their work, the researchers conducted an experiment to see whether dogs can differentiate between human odors at baseline (neutral) and when they're under stress. To do this, they collected breath and sweat samples from participants at baseline and after they had gone through a stress-inducing arithmetic task. Their stress was also validated through self-report, as well as measures such as their blood pressure and heart rate.

Samples from 36 participants were presented to trained dogs within three hours of being collected.

"In Phase One, the dog was presented with a participant's stress sample (taken immediately post-task) alongside two blanks (the sample materials without breath or sweat), and was required to identify the stress sample with an alert behavior," the researchers explained. "In Phase Two, the dog was presented with the stress sample, the same participant's baseline sample (taken pre-task), and a blank."

This photo shows the dogs during the experiments.

The idea is that if the dogs could correctly identify the stress samples in Phase Two, when the baseline samples of the participant were also around, then the baseline and stress odors were actually distinguishable to them, the researchers explained.

Incredibly, the dogs were individually able to detect the stress samples and perform the alert behavior with an impressive accuracy ranging from 90% to 96.88%. Their combined accuracy was 93.75%. This, according to the researchers, is "greater than expected by chance."

"While the dogs in this study underwent training in order to communicate that they were able to distinguish between odors, the found performances on this task suggests that there are VOC (volatile organic compound) changes induced by acute negative stress that are detectable by dogs," they wrote.

In other words, the results suggest that dogs can actually detect the changes in people's breath and sweat when they're psychologically stressed, and they can do so "with a high degree of accuracy."

Not only does this shed further light on the relationship between dogs and humans, but they say it may also have implications for service dogs that, according to PLOS, are so far trained to respond mainly to visual cues.

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