Researchers from Italy, Austria, and the UK concluded that dogs can recognize human fear by smell. The study was published in Popular Science in the Ask Us Anything section.
Scientists from the University of Naples Federico II collected sweat samples from volunteers who watched videos that induced fear, joy, or a neutral state. When exposed to the scent of a frightened person, dogs more frequently exhibited signs of stress: their heart rates increased, they sought support from their owners more often, and they were less friendly towards strangers.
Similar results were recorded at the University of Veterinary Medicine Vienna: animals that detected the smell of fear showed hesitation, approached new objects more cautiously, and held their tails lower than usual.
Veterinarian Zoe Parr-Cortes, a graduate of the University of Bristol, noted that the feeling of fear triggers chemical changes in the human body. The brain initiates the production of stress hormones—adrenaline and cortisol—which affects the composition of breath and sweat. Dogs detect these changes thanks to approximately 220 million olfactory receptors (humans have about 5 million) and the presence of the Jacobson's organ—a sensory structure that responds to pheromones.
In a study conducted by Parr-Cortes in collaboration with Dr. Nicola Rooney and Professor Mike Mendl at the Bristol Veterinary School, it was established that dogs can distinguish between the scents of people in states of stress and calm, even if they are unfamiliar with the source of the scent. Animals exposed to the scent of people with high cortisol levels exhibited caution and approached new objects more slowly.
As the researchers note, such a reaction may have evolutionary roots. The ability to detect signs of stress and fear could have helped dogs avoid threats.
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