Scientists train dogs to sniff out stress on a human’s breath

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 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 had a “scent profile” made up of volatile organic compounds (VOCs) – emitted by the body in secretions such as sweat.

There was evidence to suggest dogs may be able to detect VOCs associated with human stress.

Previous research has shown 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.

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.

Ms Kiiroja said: “Both Ivy and Callie found this work inherently motivating.”

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 90pc accuracy.

After being trained, both dogs were tested to see if they could accurately detect VOCs associated with stress.

Ivy achieved 74pc accuracy and Callie achieved 81pc accuracy, but Ivy’s performance correlated with anxiety, whereas Callie’s correlated with shame.

Ms Kiiroja said their proof-of-concept research now needed to be validated with larger studies.