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Now scientific evidence sheds more light on one of Barkley’s impressive skills in a long list of endearing traits: the ability to smell when you’re stressed.
Dogs can smell the difference between human scents when they’re stressed and when they’re relaxed, according to a study published Wednesday in the journal PLOS ONE.
Previous studies have found that dogs can smell when a person is happy or scared, but this latest study eliminated other competing scents and measured the stress levels of its human participants to increase the accuracy of the results.
The researchers first collected breath and sweat samples to use as a baseline of study participants. The subjects then performed a mental arithmetic task, counting backwards from 9,000 in units of 17 in front of two researchers for three minutes.
“If the participant answered correctly, they were given no feedback and were expected to continue, and if they gave an incorrect answer the researcher would interrupt them by saying ‘no’ and tell them the last correct answer,” said lead study author Clara Wilson. , PhD student at Queen’s University Belfast, Northern Ireland.
The study group received another breath and sweat sample after completing the task.
Additionally, the researchers reported stress levels, heart rate, and blood pressure before and after the assigned task. The dogs were shown the samples to 36 participants who reported feeling stressed and increased their heart rate and blood pressure.
The researchers submitted post-task breath and sweat samples from one to 20 people dogs along with two other blank control samples. The dogs had to choose the correct sample at least 10 times to advance to the next stage.
In the second and final phase, the study group exposed the four dogs that passed the first phase to the same samples they smelled in the first phase, along with a sample from the same individual collected before the task and a blank. When presented with these options 20 times, the dogs had to correctly identify the original “stress” odor following the task at least 80% of the time for the results to be conclusive.
The dogs chose the correct sample on 93.8% of trials, which suggested that the stress odors were quite different from the baseline samples, Wilson said.
“It was exciting to see how well the dogs were able to discriminate between these odors when the only difference was that a psychological stress response occurred,” he said.
Dogs have 220 million olfactory receptors compared to humans’ 50 million, which makes dogs “very efficient at distinguishing and identifying odors,” said Dr. Mark Freeman, a clinical assistant professor in Virginia Tech’s small animal clinical sciences department. He did not participate in the study.
Olfactory receptors are tiny nerve endings located inside the nostrils that allow you to smell, he said.
“While we don’t know why dogs developed their keen sense of smell, it probably has to do with the need to identify prey, potential threats, reproductive status and family relationships in a pack environment, among other things,” Freeman said.
Twenty pet dogs from the Belfast area of Northern Ireland were recruited and four completed the full study.
Most of the dogs didn’t finish because they showed signs of anxiety when separated from their owner or couldn’t stay focused the entire time.
If the dogs in the study had been raised from birth with the goal of de-stressing, more dogs likely would have completed the study, he said.
There was a male cocker spaniel, a female cockapoo, a type of lurcher, also known as a cross breed, and a type of terrier. Their ages ranged from 11 to 36 months.
All dogs have a keen sense of smell, but spaniels, terriers and lurchers probably used their olfactory receptors more often as hunting dogs, Freeman said. This could have been a factor in their success in the study, or it could have been a coincidence, as other breeds also have excellent olfactory skills.
Service dogs that help people with mental health conditions like anxiety and post-traumatic stress disorder may benefit from these findings, Wilson said.
“Knowing that there is a detectable olfactory component of stress can open up a debate about the value of scent-based training during stress and relaxation using human samples,” he said.
More experimentation outside the lab is needed to see how applicable the results of this research are in the real world, Wilson said.
These findings open the door for future research to investigate whether dogs distinguish between emotions, as well as how long odors are detected, he said.