Dogs Know When We’re Stressed: Here’s How

It always makes me happy when scientists substantiate something about dogs that any loving dog owner already knows – but it’s icing on the cake when we learn exactly how this happens. A study, published in PLOS One in late September, has confirmed that dogs can detect when humans are stressed. Who hasn’t received devastating news via a phone call, email, or letter and immediately, before we could say a word, had our dogs approach us and attempt to comfort us? This sounded like a no-brainer.

But the most exciting and intriguing news from the study concerned both how dogs can do this – and that they can detect stress signals from people they don’t know and will never meet – by sniffing scent samples taken from the humans. Wow!

First, dogs were trained to identify sweat and breath samples from human volunteers who had participated in a mental arithmetic exercise designed to induce stress – specifically, enough mental stress to increase their blood pressure and heart rate. (The many steps involved in teaching the dogs to detect samples from people who were stressed, and to distinguish between samples from the same person at a normal baseline and a stressed state, are described in the study; it’s a fascinating, many step process.) The researchers, from Queen’s University Belfast school of psychology, started the work with 20 dogs who had been recruited from the Belfast community; four dogs participated through the end of the trials.

In the double-blind testing phase of the study, each dog was presented with breath and sweat samples from the same participant before and after experiencing stress. The dogs correctly alerted the researchers to each person’s stress sample in nearly 94 percent of the 720 trials.

The study concludes, “These results suggest that there is a VOC [volatile organic compounds, how odors are described] profile associated with acute psychological stress that is detectable by trained dogs. Having established that this odor is detectable, further investigations may wish to apply this to real-world settings.” As some examples for potential use of this research, the study says, “Service dogs for those with anxiety, panic attack disorders, and PTSD are growing in popularity and the results of this study confirm that trained dogs are able to detect the physiological processes associated with an aspect of these conditions from odor alone.”

Again, while this study suggests that there are endless potential applications for us to harness the extraordinary ability of dogs to detect odors, I am personally thrilled to have information about exactly how dogs can detect and identify how humans are feeling – even humans they don’t know.

As just one silly example, this helps dispel that old trope about how dogs just “know when you’re scared of them” – especially since people who imparted this “wisdom” historically suggested that a person needs to dominate the dog as a response, lest the dog use his information about your fear to dominate you. What a bunch of bull! The study suggests that dogs can literally smell the compounds emitted by a stressed person; can you imagine how scary and/or strange it must be for dogs to meet humans that smell (to them) scared out of their minds? I wonder if a person who seems outwardly normal but is experiencing all the physiological symptoms of stress, seems to a dog like a human who is in full panic mode seems to us!