Dogs can smell their humans' stress, and it makes them sad

By Sara Novak published 31 minutes ago

Dogs can smell when people are stressed, and it seems to make them feel downhearted.



A black lab on the couch looks off to the side with a sad expression
A new study shows that dogs pick up on our emotions through their sense of smell. (Image credit: Catherine Falls Commercial via Getty Images)


Humans and dogs have been close companions for perhaps 30,000 years, according to anthropological and DNA evidence. So it would make sense that dogs would be uniquely qualified to interpret human emotion. They have evolved to read verbal and visual cues from their owners, and previous research has shown that with their acute sense of smell, they can even detect the odor of stress in human sweat. Now researchers have found that not only can dogs smell stress—in this case represented by higher levels of the hormone cortisol—they also react to it emotionally.

For the new study, published Monday in Scientific Reports, scientists at the University of Bristol in England recruited 18 dogs of varying breeds, along with their owners. Eleven volunteers who were unfamiliar to the dogs were put through a stress test involving public speaking and arithmetic while samples of their underarm sweat were gathered on pieces of cloth. Next, the human participants underwent a relaxation exercise that included watching a nature video on a beanbag chair under dim lighting, after which new sweat samples were taken. Sweat samples from three of these volunteers were used in the study.

Participating canines were put into three groups and smelled sweat samples from one of the three volunteers. Prior to doing so, the dogs were trained to know that a food bowl at one location contained a treat and that a bowl at another location did not. During testing, bowls that did not contain a treat were sometimes placed in one of three "ambiguous" locations. In one testing session, when the dogs smelled the sample from a stressed volunteer, compared with the scent of a cloth without a sample, they were less likely to approach the bowl in one of the ambiguous locations, suggesting that they thought this bowl did not contain a treat. Previous research has shown that an expectation of a negative outcome reflects a down mood in dogs.

The results imply that when dogs are around stressed individuals, they're more pessimistic about uncertain situations, whereas proximity to people with the relaxed odor does not have this effect, says Zoe Parr-Cortes, lead study author and a Ph.D. student at Bristol Veterinary School at the University of Bristol. "For thousands of years, dogs have learned to live with us, and a lot of their evolution has been alongside us. Both humans and dogs are social animals, and there's an emotional contagion between us," she says. "Being able to sense stress from another member of the pack was likely beneficial because it alerted them of a threat that another member of the group had already detected."

More:
https://www.livescience.com/animals/dogs/dogs-can-smell-their-humans-stress-and-it-makes-them-sad