If you’ve been lucky enough to meet a friendly horse, then you know they lead with their noses—the first thing they want to do with a new acquaintance, human or otherwise, is to get a good snuffle in. A study just published in PLOS One by a team of animal behavior researchers in France demonstrates that it’s not just for fun-with-scents; horses are getting a read on your emotional state, which in turn affects their behavior toward you.
In earlier research published in Nature, these researchers demonstrated that horses could discriminate between human emotions of fear versus joy. Horses were exposed to the odors of human sweat on cotton pads after study participants had either watched a horror movie or a comedy movie. After habituation to either “fear odor” or “joy odor,” horses spent more time sniffing the novel scent (see video here).
The new research built on those findings by evaluating the behavior and physiology of horses when exposed to human odors. Odor samples were collected from adult participants who had abstained from any scented body products during the lead-up to the study. Then, 43 Welsh mares were randomly assigned to the three experimental groups of fear odors, joy odors, or a control (in this case, a cotton pad with no human scent).
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A naïve observer noted horse behavior during a range of interactions—grooming of the horse on its withers and neck; standing near the horse; startling the horse with the sudden opening of an umbrella; and presenting the horse with a colorful, novel object.
The results showed that, in smelling the fear odor, horses had heightened fear responses, which caused them to reduce interaction with humans. Fear responses manifested through startle reactions, raised heart rates, and more staring at the “intruding” person. For example, the maximum heart rate of horses in the fear group was significantly higher than that of horses in the joy or control group. Horses sniffing fear odors also touched the participants less, stared more at the novel objects, and were more easily startled by the umbrella.
“These findings have practical implications regarding the significance of handlers’ emotional states and its transmission through odors during human-horse interactions,” wrote the study authors. They propose that further research on other domestic animals could help understand the extent of the role of olfaction in interactions between humans and other species.
Just know this for now: If you smell like fear when you approach an animal, it may respond in kind. 
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Lead image: JW.photography31 / Shutterstock
