Stress is transmitted: Dogs can also be pessimists.
When humans are under high stress, they often begin to sweat. A new study shows that the resulting sweat odor influences the behavior of dogs, with noticeable consequences.
High stress levels in humans are associated with physical changes: We tense up, get headaches, heart palpitations, or have elevated blood pressure. Hormones like cortisol and epinephrine are also released in increased amounts, and we sweat. Researchers at the University of Bristol have concluded that dogs can smell this. When the animals sniff out stress-induced sweating, they often make more pessimistic decisions. The British research team published their results in the journal "Scientific Reports" at the end of July 2024.
Optimist or pessimist: Is the bowl empty or full?
For their study, the scientists conducted various experiments with 18 dogs and their owners to investigate how stress odors from humans affect dogs' learning and emotional states.
Understanding how human stress affects dog well-being is an important consideration for dogs in kennels in, the training of service dogs, and dogs for professional roles such as assistance dogs.
In the study, the researchers taught the animals that a food bowl in one location always contained something edible, while a food bowl in another was always empty. Once the dog had learned and internalized this distinction, the dog approached the area with the whole bowl more quickly.
The researchers then tested what happened when a third or fourth food bowl, previously unfamiliar to the animal, was added. Would the dog immediately expect food in the new bowl? If the dogs approached the new bowls quickly, the researchers interpreted this behavior as an optimistic decision and a sign of a positive emotional state. On the other hand, scientists interpret a slow approach as a sign of a pessimistic emotional state.
Stress smell affects the behavior of dogs.
The researchers then repeated these experiments with the animals and added another factor: odor samples. How would human odors influence the dogs' decisions?
Again, the dogs were presented with different food bowls, but this time in combination with sweat or breath samples from stressed and unstressed people.
Result: The British scientists observed that the stress odor caused the dogs to approach the unfamiliar food bowls closest to the usual location of the empty bowl more slowly. An effect that was not observed when the animals were exposed to the sweat and breath samples of relaxed humans.
Pessimism as a way to avoid disappointment
The results suggest that the stress odor increased the dogs' expectation that the new bowl would not contain food. The researchers suspect that this "pessimistic" reaction reflects a negative emotional state and may be a way for the dog to conserve energy and avoid disappointment.
Dog owners know how much their pets react to their emotions. Still, we show here that even the smell of a stressed, unfamiliar person influences a dog's emotional state, perception of rewards, and ability to learn. Handlers often describe stress as transmitted via the leash, but we have shown that it can also be transmitted through the air.