Dogs can detect humans' stress levels by smelling their breath

Scientists have discovered that specially trained dogs may be able to detect the early signs of an impending PTSD stress flashback by sniffing out specific compounds in a person’s breath.

This finding could lead to a new way for service dogs to assist individuals struggling with the debilitating symptoms of post-traumatic stress disorder (PTSD).

Dogs detect stress levels by sniffing VOCs

The research, led by Laura Kiiroja of Dalhousie University and published in Frontiers in Allergy, brought together expertise from Dr. Sherry Stewart’s clinical psychology lab and Dr. Simon Gadbois’ canine olfaction lab.

The collaboration aimed to investigate whether dogs could learn to detect volatile organic compounds (VOCs) associated with PTSD symptoms.

“PTSD service dogs are already trained to assist people during episodes of distress,” said Kiiroja. “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.”

The scent of stress and PTSD

To conduct the study, the researchers recruited 26 human participants, 54% of whom met the diagnostic requirements for PTSD stress levels.

These individuals provided breath samples while wearing different facemasks — one worn during a calm state and another worn while recalling their traumatic experiences.

Meanwhile, 25 pet dogs were recruited for scent-detection training, with two standout performers, Ivy and Callie, completing the study.

These skilled dogs were trained to recognize and detect the target stress odor from pieces of the facemasks, achieving an impressive 90% accuracy in distinguishing between stressed and non-stressed samples.

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

Detecting different types of stress

When presented with a series of samples to test their accuracy, Ivy achieved 74% accuracy, while Callie achieved 81%. Interestingly, the dogs seemed to have slightly different ideas of what constituted a “stressed” breath sample.

“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),” explained Kiiroja.

“This is important knowledge for training service dogs, as alerting to early-onset PTSD symptoms requires sensitivity to sympathetic-adreno-medullar axis hormones.”

Potential for earlier intervention

PTSD service dogs are already trained to help patients by alerting to and interrupting episodes when their companions are struggling with symptoms.

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

“This is a multidisciplinary collaboration between Dr Sherry Stewart’s clinical psychology lab and Dr Simon Gadbois’ canine olfaction lab, both at Dalhousie University,” said Kiiroja. “Neither lab could have done this work on their own. We brought together two distinct sets of expertise.”

Implications and further study

While this proof-of-concept study provides exciting insights, the researchers acknowledge that validation studies with larger sample sizes are needed to confirm the dogs’ ability to reliably detect stress VOCs across different contexts.

“With 40 sample sets, ours is a proof-of-concept study that needs to be validated by studies with larger sample sizes,” cautioned Kiiroja.

“In addition to enrolling more participants, validation studies should collect samples from a higher number of stressful events to confirm dogs‘ ability to reliably detect stress VOCs in the breath of one human across different contexts,” Kiiroja concluded.

The team plans to carry out further experiments to confirm the involvement of the sympathetic-adreno-medullar axis in the dogs’ detection of stress VOCs.

What the future holds for dogs and stress detection

In summary, this fascinating study conducted by Laura Kiiroja and her team at Dalhousie University sheds light on the potential for specially trained dogs to detect the early signs of PTSD stress flashbacks. This occurs through canine olfactory analysis of stress-related VOCs in human breath.

Their discovery paves the way for more effective interventions by service dogs, allowing them to interrupt episodes at an earlier stage and provide better support for individuals struggling with PTSD.

As the researchers continue to investigate the involvement of specific hormonal pathways in the dogs’ detection abilities, the future of PTSD management looks promising, with the possibility of earlier detection and more targeted assistance from our canine companions.

The full study was published in the journal Frontiers in Allergy.

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