They can sniff out cancer, COVID, corpses and the forgotten shrink-wrapped cheese stick in the bottom of your pack in the back of your closet. But can dogs smell stress? What about happiness? And what does that mean for the health of our furry family members—and for the dog-human relationship? Read on to find out, including the results of a recent study we found as intriguing as your dog may find a well-traveled sock.
What Can Your Dog Smell or Sense About Your Emotions?
Compared to our relatively useless snouts, dogs are super sniffers. Humans have 50 million olfactory receptors in our noses. Dogs have more than 220 million. Think that bacon smells good sizzling in the pan? Imagine if you could smell it, literally, millions of times better. It’s a wonder all dogs don’t melt into puddles of drool every time we make breakfast.
We’ve long known that dogs can sense human fear by smelling the chemicals we secrete when afraid and by reading micromovements of our bodies and face. And, most every pet parent can think of a time when a furry chin was planted on a lap or a gentle paw rested on a chest just when we needed it most. But science had not divulged any evidence regarding canine’s ability to smell stress in humans—until now. A new study published in the journal PLOS ONE[https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0274143] suggests dogs can in fact, smell when humans are stressed.
From a larger group of wagging recruits, scientists at Queen’s University Belfast in the U.K. selected four dogs who, after initial testing, showed they were highly motivated to choose from different samples of human odors. The test crew consisted of Fingal, a male brindle rescue lurcher/hound mix; Soot, a female mixed-terrier type rescue; Treo a male Cocker spaniel and Winnie, a female cockapoo.
Their human counterparts were 36 nonsmokers who did not eat or drink anything before the test. Researchers collected sweat and breath samples from the human participants before and after they had to perform a difficult math problem. The researchers used samples from the subjects who showed signs of stress from the math—increases in blood pressure and heart rate. To collect the samples, gauze was wiped on the back of their necks and placed in a sterile glass vial. Then, they exhaled three times into the vial.
Separately, the researchers used clickers to train the dogs to recognize the stressed sample. For the test, they presented the dogs with three different scents, a standard piece of gauze, a sample from an unstressed human and a sample from a stressed human.
How’d they do? Fingal, Soot, Treo and Winnie correctly alerted the researchers to the stress samples in nearly 94 percent of the 720 trials.
“This study provides further evidence of the extraordinary capabilities of ‘man’s best friend,’ the study’s first author, animal psychologist Clara Wilson, told NBC News.“While it is likely that in a real-life context dogs are picking up on our stress from a variety of context cues, we have shown using a laboratory study that there is a confirmed odor component that is likely contributing to dogs’ ability to sense when we are stressed.”
What Emotions Can Dogs Sense?
Even without a single sniff, dogs have a remarkable ability to read our facial expressions and body cues. A study published in a 2018 issue of the journal Learning and Behavior found that dogs respond to human faces that express six basic emotions—anger, fear, happiness, sadness, surprise and disgust—with changes in their gaze and heart rate.
