Dogs can detect trauma stress by smelling humans’ breath, study shows

Service dogs trained to recognize oncoming flashbacks of Post-Traumatic Stress Disorder, or PTSD, in people also can be taught to detect these episodes by sniffing their breath, a new pilot study shows.  The study, conducted at Dalhousie University in Halifax, Nova Scotia, Canada, was published in April 2024 in Frontiers in Allergy.

Earlier research already established that canines’ sensitive noses can detect the early warning signs of many potentially dangerous medical situations, such as an impending seizure or sudden low blood sugar.  However, until this investigation, it was unknown whether dogs’ heightened sense of smell can interrupt a PTSD episode or alert their human companions to these oncoming symptoms spurred by reminders of trauma, the study’s first author, Laura Kiiroja, a Doctoral Student at Dalhousie University, told the United Press International (UPI) via e-mail.

The researchers described PTSD as “an impairing mental health condition with high prevalence among military and general populations alike.”  PTSD service dogs “are trained to respond to minute behavioral and physical cues, such as fidgeting, fist-clenching, muscle-twitching or elevated respiration and heart rate,” Kiiroja said.  “Our study showed that at least some dogs can also detect these episodes via breath.”  If dogs reacted to stress markers on the breath, researchers suspected the canines could potentially halt PTSD episodes at an earlier stage, making their interventions more effective.

All humans have a “scent profile” of volatile organic compounds – molecules emitted in secretions such as sweat and influenced by genetics, age, activities, and other variables.  Some evidence suggests that dogs may be capable of detecting these compounds, which are linked to human stress.  However, earlier studies had not looked into whether dogs could learn to detect these compounds associated with PTSD symptoms.

The study is a collaboration between two (2) distinct sets of expertise – the clinical psychology lab led by Sherry Stewart and the canine olfaction lab spearheaded by Simon Gadbois, both at Dalhousie University.  Neither one could have conducted this research on their own, Kiiroja said.  To carry out this investigation, the researchers recruited 26 humans as scent donors.  These individuals also were participating in a study about the reactions of people who experienced trauma to reminders of a catastrophic event, and 54% met the diagnostic criteria for PTSD.  To donate scents, they attended sessions at which they were reminded of their trauma experiences while wearing different facemasks.  Participants also answered a questionnaire about their stress levels and emotions.  Meanwhile, the scientists recruited 25 pet dogs to train in scent detection.  Two (2) of them – Ivy and Callie – were skilled and motivated enough to complete the study.  Both dogs were taught to recognize the target odor from pieces of the facemasks, achieving 90% accuracy in discriminating between a stressed and a non-stressed sample.  The dogs then were presented with a series of samples, one at a time, to determine if they could still correctly detect the volatile organic compounds associated with stress.  In this second experiment, Ivy’s rate of accuracy was 74% and Callie’s was 81%.  “Perhaps the most interesting is the result that our two dogs appeared to respond to different olfactory biomarkers.  Stress is not just about cortisol, and our dogs attested to that,” Kiiroja said.

“Although they both performed at very high accuracy, they seemed to have a slightly different idea of what they considered a ‘stressed’ breath sample,” she added.  “Ivy’s performance was correlated with participants’ self-reported anxiety and Callie’s performance was correlated with participants’ self-reported shame.”  Kiiroja, a native of Estonia, said she enrolled in the Doctoral Program at Dalhousie University to pursue her passion of studying canine behavior and cognition.  “It made me all the more happy that my Ph.D. project enabled contributing to the welfare of our own species both by expanding our knowledge on dogs’ potential in biomedicine, particularly in mental health, and adding to the evidence base of service dogs as a complementary treatment for PTSD,” she said.

Dr. Jerry Klein, Chief Veterinarian at the American Kennel Club in New York City, who was not involved in the research, told UPI via email it “is intriguing and hopeful that dogs may one day be able to offer assistance to people suffering from PTSD or perhaps other forms of trauma.  These tests will need to be validated on a greater level.”

One thing is clear, though:  Dogs typically possess a much greater sense of smell than humans, with 300 million olfactory receptors in their noses compared to humans’ six million receptors, Klein said.  However, “not all dogs may have the same ability or inclination to use these natural gifts in the same way,” he said, noting that service dogs are chosen based on their skills and willingness to be trained for utilizing these factors.  “Often, these dogs come from similar breeds or types of dogs, or even subsets of families of dogs, though there are exceptions to every rule,” Klein added.

A few small studies have shown that dogs can support people with PTSD in having greater independence, more confidence, lower hypervigilance and higher success in relationships, Alice Connors-Kellgren, a Clinical Psychologist at Tufts Medical Center in Boston, told UPI via e-mail.  “Hypervigilance refers to the heightened awareness of possible danger that people who have experienced trauma develop,” Connors-Kellgren said.  She added that “dogs can be an incredible support to people with all kinds mental health diagnoses.”  However, “therapy dogs and service dogs are trained from a young age to be on the lookout for signs of distress and to respond to people’s signals that they need help with a task.”  Other dogs can use smell to detect cancer and have been specifically trained for this purpose.  It is not something that any dog would be able to do without training, Connors-Kellgren noted.

Nancy Smyth, a professor in the University at Buffalo School of Social Work, told UPI via e-mail that the current study is “too small to have much significance except to encourage more research investigating whether or not more dogs, especially service dogs, can be trained to detect human scent profiles associated with PTSD.”  Smyth added that if future research proves the reliability of trained canines’ usefulness in performing this task, “it could really enhance the ability of these dogs to provide support to people struggling with PTSD symptoms.”

REFERENCE:  United Press International (UPI); Susan Kreimer, 28 MAR 2024