Dogs may be able to sniff out an oncoming flashback caused by post traumatic stress disorder (PTSD), research suggests.
PTSD is a mental health condition caused by stressful, frightening or distressing events, with those afflicted often reliving these moments through nightmares and flashbacks.
Scientists have now trained dogs to recognise the scent in the breath of people reflecting on past traumatic experiences.
They said the findings, published in the journal Frontiers in Allergy, could make PTSD assistance dogs more effective.
Laura Kiiroja, of the department of psychology and neuroscience at Dalhousie University in Canada, said: “PTSD service dogs are already trained to assist people during episodes of distress.
“However, dogs are currently trained to respond to behavioural and physical cues.
“Our study showed that at least some dogs can also detect these episodes via breath.”
The researchers said all humans have a “scent profile” made up of volatile organic compounds (VOCs) – which are emitted by the body in secretions such as sweat.
They said there is some evidence that suggest dogs may be capable of detecting VOCs associated with human stress.
Previous research has shown that dogs have the ability to detect diseases such as cancer as well as early signs of potentially dangerous medical situations, such as an impending seizure or sudden hypoglycemia (when blood sugar levels become abnormally low).
For the study, the team recruited 26 people, more than half of whom met the diagnostic requirements for PTSD.
The individuals were asked to breathe into a facemask while recalling past traumatic events.
The team recruited 25 dogs to train in scent detection but only two – Ivy and Callie – were skilled and motivated enough to complete the experiments, the researchers said.
Ms Kiiroja said: “Both Ivy and Callie found this work inherently motivating.
“Their limitless appetite for delicious treats was also an asset.
“In fact, it was much harder to convince them to take a break than to commence work.
“Callie in particular made sure there was no dilly-dallying.”
The researchers said both dogs were trained to recognise the odour from the facemasks.
The canines were able to tell the difference between stressed and non-stressed facemask samples, with up to 90% accuracy, according to the researchers.
After being trained, both dogs were tested to see if they could accurately detect VOCs associated with stress.
In this experiment, Ivy achieved 74% accuracy and Callie achieved 81% accuracy, the team said, but Ivy’s performance correlated with anxiety, whereas Callie’s correlated with shame.
Ms Kiiroja said: “Although both dogs performed at very high accuracy, they seemed to have a slightly different idea of what they considered a ‘stressed’ breath sample.”
She said the team believes Ivy was more attuned to a part of the autonomic nervous system responsible for hormones associated with “fight or flight” response, such as adrenaline.
Meanwhile, Callie was oriented towards a complex neuroendocrine system involved in the body’s response to stress, which is associated with the hormone cortisol.
Ms Kiiroja said their proof-of-concept research now needs to be validated with larger studies.