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Now there’s scientific evidence that sheds more light on one of Barkley’s fascinating skills: the ability to smell when you’re stressed.

According to a study published Wednesday in the journal PLOS ONE, dogs can distinguish between the scents of humans when they are stressed and when they are calm.

Previous research has found that dogs can smell when a person is happy or fearful, but this latest study eliminated other competing scents and measured the stress levels of its human participants to increase the accuracy of the results.

Researchers first collected breath and sweat samples from study participants to use as a baseline. Then, these people performed a mental arithmetic task, counting backwards from 9,000 in units of 17 for three minutes in front of two researchers.

“If the participant answered correctly, they were given no feedback and expected to continue, and if they answered incorrectly, the researcher would interrupt with a ‘no’ and tell them their last correct answer,” said lead study author Clara. Wilson said. , a doctoral candidate at Queen’s University Belfast in Northern Ireland.

The study team collected another breath and sweat sample after the task was completed.

In addition, the researchers recorded stress levels, heart rate, and blood pressure before and after the assigned task. Thirty-six participants who reported feeling stressed and had increased heart rate and blood pressure were exposed to dogs.

The researchers submitted up to 20 post-task breath and sweat samples from one individual Dogs with two other blank control samples. Dogs must choose the correct pattern at least seven out of 10 times to advance to the next stage.

In the second and final phase, the study team showed the four dogs that had passed the first phase the same samples they had sewn in the first phase and a sample collected before the task from the same individual and a blank. With these alternatives presented 20 times, dogs needed at least 80% of the time to successfully identify the original post-task “stress” scent for the effect to be conclusive.

The dogs chose the correct sample in 93.8% of trials, indicating that the stress odor was significantly different from the baseline samples, Wilson said.

“It was interesting to see how well the dogs were able to discriminate between these odors, the only difference was the stress response,” she said.

Dogs have 220 million olfactory receptors, compared to humans’ 50 million, which makes dogs “extremely effective at distinguishing and identifying odors,” Dr. said Mark Freeman, a clinical assistant professor in the small animal clinical sciences department at Virginia Tech in Blacksburg. He was not engaged in studies.

Olfactory receptors are tiny nerves located in your nostrils that allow you to smell, he said.

“We can’t know for sure why dogs developed such a strong sense of smell, but it’s probably related to the need to identify prey, potential threats, reproductive status, and familial relationships among others,” Freeman said.

Twenty pet dogs were recruited from Belfast, Northern Ireland, and four completed the entire study.

Most of the dogs failed to finish because either they showed signs of anxiety when separated from their owner or they could not concentrate the whole time.

More dogs likely would have completed the study if the dogs in the study had been raised from birth with the goal of de-stressing them, he said.

There was a male Cocker Spaniel, a female Cockapoo, a male Lucher type, also known as a crossbred hound, and a female Terrier type. Their ages ranged from 11 to 36 months.

All dogs have a keen sense of smell, but spaniels, terriers and lurchers may have used their olfactory receptors more regularly for hunting dogs, Freeman said. This may be the reason for their success in studies, or it may be a coincidence because other breeds such as retrievers also have excellent smelling skills.

Service dogs helping people with mental health conditions such as anxiety and post-traumatic stress disorder could benefit from the findings, Wilson said.

“Knowing that there is a detectable odor component to stress, one can discuss the value of scent-based training using samples of individuals during periods of stress versus calm,” she said.

More experiments outside the lab are needed to see how applicable the study’s results are in the real world, Wilson said.

The findings also open the door to future research to test whether dogs can discriminate between emotions, as well as how long odors can be detected, she said.

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