Dogs can be taught to recognize the scent of trauma reactions on the breath, study shows

According to a new study from Dalhousie University, researchers have found evidence that service dogs might be able to sniff out an oncoming post-traumatic stress disorder (PTSD) flashback by teaching them to alert the breath of people.

"PTSD service dogs are already trained to assist people during episodes of distress," said researcher Laura Kiiroja of Dalhousie University.

"However, dogs are currently trained to respond to behavioral and physical cues. Our study showed that at least some dogs can also detect these episodes via breath."

Researchers said if dogs could respond to stress markers on the breath, they could potentially interrupt episodes at an earlier stage, making their interventions more effective.

All humans have a 'scent profile' of volatile organic compounds, molecules emitted by the body in secretions like sweat that are influenced by our genetics, age, activities, and other variables.

There is some evidence that dogs may be capable of detecting VOCs linked to human stress. However, no previous studies have investigated whether dogs could learn to detect VOCs associated with PTSD symptoms.

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To carry out the study, scientists recruited 26 humans as scent donors.

The participants chosen were also taking part in a study about the reactions of people who have experienced trauma to reminders of that trauma; 54 per cent met the diagnostic requirements for PTSD.

To donate scents, participants attended sessions where they were reminded of their trauma experiences while wearing different facemasks.

One facemask provided a calm breath sample that acted as the control, and another, which was worn while the participants recalled their trauma, provided a target breath sample.

Participants also completed a questionnaire about their stress levels and their emotions.

Scientists then recruited 25 pet dogs to train in scent detection. Researchers say only two of the dogs were skilled and motivated enough to complete the study: Ivy and Callie.

Ivy and Callie were then trained to recognize the target odor from pieces of the facemasks, achieving 90 per cent accuracy in discriminating between a stressed and a non-stressed sample.

Then the two dogs were presented with a series of samples, one sample at a time, to see if they could still accurately detect the stress VOCs.

A photo of Callie, a German Shepherd. (Courtesy: Dalhousie University)

Ivy achieved 74 per cent accuracy and Callie achieved 81 per cent accuracy.

Researchers say when they compared Callie and Ivy's successful identifications with the human participants' self-reported emotions it revealed that Ivy's performance correlated with anxiety, whereas Callie's correlated with shame.

"Although both dogs performed at very high accuracy, they seemed to have a slightly different idea of what they considered a 'stressed' breath sample," said Kiiroja.

"We speculated that Ivy was attuned to sympathetic-adreno-medullar axis hormones (like adrenaline) and Callie was oriented to the hypothalamo-pituitary-adrenal axis hormones (like cortisol). This is important knowledge for training service dogs, as alerting to early-onset PTSD symptoms requires sensitivity to sympathetic-adreno-medullar axis hormones."

According to the release, researchers plan to carry out experiments to confirm the involvement of the sympathetic-adreno-medullar axis.