Have you ever felt that a horse could smell your fear? Recent study results suggest he probably did—quite literally.
Horses can smell specific odors in human sweat that reflect emotions like fear and happiness, Italian researchers have learned. And that finding could open doors to a whole new way of understanding emotion transfer between species—and specifically, from human to horse.
“We noticed that horses had increased levels of arousal when they smelled human ‘fear’ and ‘happiness’ odors,” said Paolo Baragli, DVM, PhD, a researcher in the University of Pisa Department of Veterinary Sciences, in Italy.
“Even if these results are preliminary, the data support the hypothesis that avoidance or escape behaviors in horses could be due, in part, to an odor communication system at an interspecies level,” he said. “And that’s the wide window we’ve opened. Do emotional exchanges have multichannel pathways between species? Our research suggests they certainly might.”
The study complements previous research that revealed that dogs can also pick up the scents of humans experiencing fear or happiness, and react differently to those odors, said Biagio D’Aniello, PhD, of the University of Naples Federico II Department of Biology, also in Italy. Humans, however, appear to be “less skilled” at detecting such odors, he added.
In their study, Baragli; D’Aniello; Antonio Lanata, PhD, also of the University of Pisa; and colleagues studied how horses reacted to underarm sweat samples from young men watching movies. The volunteers, who were instructed to use no perfumed products for several days in advance, watched either horror films that evoked fear or “feel-good” films that evoked happiness. The scientists collected their sweat samples on cotton gauze and then presented them to seven horses of different breeds and ages. They recorded horses’ cardiac activity as they smelled the different sweat pads compared to an unscented sweat pad, used as a control.
The horses had clear changes in autonomous nervous system activity when they smelled the human fear and happiness odors, Baragli and D’Aniello said. However, they haven’t yet studied the valence—the specific “direction” the horses’ emotions took during the testing phase, they said. In other words, they don’t know yet whether the horses’ response to human fear is to become more fearful themselves or if their response to human happiness is to have more positive emotions themselves.
In dogs, human fear-related odors coming from strangers caused them to tend to stay closer to their owners, D’Aniello said. But when a stranger’s odors were related to happiness, the dogs tended to be more friendly and outgoing to the stranger. Further research in horses could give better insight into the emotional valence they experience when smelling “fear” or “happiness” in humans, he added.
Practically speaking, however, it might be hard to determine the effect of our smells on horses when we experience strong emotions, Baragli said. Humans usually have a variety of smells coming from beauty and cleaning products, food, and the home environment—not to mention the stable environment.
“The point isn’t really to have a direct practical application in riding centers,” Baragli said. “However, the study does draw our attention to certain points worth considering about the transfer of emotions between species—which seems to be multifactorial, including sights, sounds, touch, and smell.”
And it could give clues about how our odors—whatever they might be—could affect horses’ emotions, he added. “For example, if you use your whip incorrectly … that horse might learn to associate your combination of smells (personal smells, shampoo, food, and more) with a negative experience,” he said.
On the flip side, an association of positive emotions with our smells could be great for the human-horse relationship—but only if we’re making sure the environment allows that to happen. Welfare-compromising training tactics or stable management could reduce a horse’s sensitivity to picking up “good” associations through smells, said Baragli.
“If you feel bad psychologically, your ability to perceive the inner state of others could be flawed due to poor perception or could disappear entirely,” he said.
The study, “A Case for the Interspecies Transfer of Emotions: A Preliminary Investigation on How Humans Odors Modify Reactions of the Autonomic Nervous System in Horses,” was published in the 2018 40th Annual International Conference of the IEEE Engineering in Medicine and Biology Society.