Do you believe it? Human stress has a smell, and dogs with sensitive noses can detect it. A recent study found that not only can dogs smell this odor, but they can also be significantly affected, leading to more pessimistic choices.
The University of Bristol in the United Kingdom announced on July 22 that a study led by researchers from the university for the first time examined how human stress odors affect the learning and emotional states of dogs.
In this study, researchers recruited 18 pairs of dogs and their owners to participate in a series of experiments involving different human odors. During the experiments, these dogs received training. When a bowl was placed in one location with food inside, and in another location empty without food, the dogs learned to distinguish between the two.
Once the dogs understood the difference between the locations of these bowls, they approached the location with food faster than the location without food. Researchers then added new positions between these two locations to test the dogs’ speed in approaching these positions.
If the dogs approached these new positions quickly, it indicated optimism; while approaching slowly reflected their pessimistic mood. Researchers collected sweat and breath samples from the owners under stressful (doing math tests) or relaxed (listening to music) conditions, and then repeated the experiment with each dog under the influence of these odor samples and odorless conditions.
Researchers found that the smell of stress made dogs approach the new position closest to the empty bowl location more slowly, while the smell of relaxation did not elicit this reaction. These findings suggest that the smell of stress may increase the dogs’ expectation of no food at this new position, just like the nearby empty bowl location.
Researchers believe that this pessimistic response reflects a negative emotional state, possibly a way for dogs to conserve energy and avoid disappointment.
The research team also found that dogs continued to improve their understanding of whether there was food in the initial two bowls they were trained on, and when the smell of stress was present, their rate of improvement was faster.
Nicola Rooney, senior lecturer in wildlife and conservation at the University of Bristol’s School of Veterinary Sciences and the lead author of the study, said that understanding how human stress affects dogs’ health is an important consideration for puppies in kennels and for dogs trained as companion dogs and assistance dogs.
Rooney said, “Dog owners know how sensitive their pets are to their emotions, but here, our research suggests that even the odor of a stressed, unfamiliar person can affect a dog’s emotional state, reward perception, and learning abilities.”
The above research results were published in the journal “Scientific Reports” on July 22.