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In 2022, scientists recruited 36 people for a study in Northern Ireland. They needed the gathered volunteers to be stressed. So the researchers exposed them to the most psychologically tortuous activity they could get past their ethics department: maths.

Police handlers pet their COVID-19 sniffer dogs after a demonstration in Chile.Credit: AP

The volunteers breathed into a glass tube before and after scientists asked them to complete complex arithmetic (counting backwards from 9000 by units of 17). Researchers also wiped the back of the volunteer’s necks with gauze.

Then they brought in Treo, Fingal, Soot and Winnie, dogs that had been taught to identify the odour samples of stressed humans. When shown the tubes containing the breath and gauze of stressed participants, along with control tubes, the dogs correctly chose the stressed sample in 94 per cent of 720 trials.

The finding that dogs could differentiate a relaxed human’s scent from a stressed one made international headlines. Now a new study, published last week, has found dogs can sniff out trauma responses in people with PTSD.

Two pet dogs, Ivy and Callie, were recruited to see if they could be taught to identify the face masks worn by people with PTSD who had attended a session in which they were reminded of their trauma. The dogs did so with accuracy between 80 and 90 per cent. Ivy, a golden retriever, seemed to clock onto anxiety and adrenaline, while Callie, a German Shepherd/Belgian Malinois mix, focused more on cortisol and shame, the researchers said.

“Both Ivy and Callie found this work inherently motivating,” said research lead Laura Kiiroja, from Dalhousie University in Canada. “Their limitless appetite for delicious treats was also an asset.”

The fact the dogs were so good at the task has redoubled scientists’ hope that support dogs could be taught to sense an impending trauma response by the breath, and intervene even before the human in question has perceived their rising stress.