Horses really can smell our fear, new study finds

Horses can detect fear in humans by their scent, becoming more likely to startle and be more wary of frightened people, a new study suggests.

Researchers collected samples of odorous compounds from the armpits of human study participants, then observed how the horses behaved when exposed to the different odors during standardized tests, according to a study published Wednesday in the journal PLOS One..

While previous research has shown that horses can pick up on human emotions through speech and facial expressions, the idea that they can sense our fear has remained only a theory due to the difficulties of studying smell, said the study’s lead author, Plotine Jardat, a researcher at the French Institute of Horse and Equestrian (IFCE).

“As humans, we’re not really aware of all the smells around us compared to what other animals seem to perceive, so it’s not that easy to study,” Jardat told CNN.

To overcome this problem, researchers developed a new method of placing cotton pads under the armpits of human study participants, where the odorous compounds are released by the sweat glands.

Samples were taken from people watching a scary video and a happy video, as well as a neutral sample, and these pads were then placed on the nostrils of 43 different female horses, held in place by small nets.

The researchers took care to avoid contamination with other odorous compounds by ensuring that the swabs were only handled by the human providing the sample, and that the compounds were preserved by freezing the swabs, Jardat said.

The horses were then exposed to a series of tests conducted by experimenters familiar with animals – for example, to find out whether they would freely approach a human in their enclosure or whether they would startle at the sudden opening of an umbrella.

The researchers observed the horses’ behavior and collected data on their heart rates and the level of cortisol in their saliva, a key biomarker of stress.

The analysis showed that horse behavior and physiology were influenced by human odorous compounds.

Researchers observed that horses exposed to odorous compounds produced by volunteers who had viewed frightening images were more likely to startle more easily and less likely to approach people or investigate unfamiliar objects.

“Frightening odors from humans amplify horses’ reactions,” Jardat explains.

“What’s important is that horses can feel what we feel, even if they can’t hear or see us,” she said.

Léa Lansade, co-author of the study and director of research at the National Institute for Research on Agriculture, Food and the Environment (INRAE), said the study provides evidence of “emotional contagion” between species.

And there are practical implications for those who ride or handle horses, including “recognition of the importance of the emotional state of handlers and its potential transmission through chemosignals during human-horse interactions,” according to the article.

Although as humans we can’t control the emotional scents we emit, Lansade said in a statement to CNN that riders should “focus on relaxing, so you can ride calmly and without fear.”

Next, the researchers plan to study whether humans are sensitive to odorous compounds produced by horses when they feel certain emotions, and to study the chemical compounds involved.

They also plan to determine whether chemical communication between humans and horses is specific to fear, or if it also occurs with other emotions.

“We started with fear because it’s an emotion that we really expect other animals to feel as well, because what fear allows you to do is detect danger and avoid it,” said Jardat, who added that the researchers planned to investigate sadness and disgust.

“Even if they (horses) don’t feel these emotions precisely, they might sense differences from humans who feel these emotions, and that might mean something to them,” she added.

Gemma Pearson, a specialist in veterinary behavioral medicine (equine) at the Royal College of Veterinary Surgeons (RCVS) and lecturer at the Royal (Dick) School of Veterinary Studies, Scotland, who was not involved in the study, welcomed the research.

“This is a nice study that builds on previous work from this group and meets a typical standard of proof for equine behavior research,” she told CNN. “This group took care to control for confounding variables in this study that could lead to an incorrect result.”

Pearson also pointed out that horses use their sense of smell in conjunction with other sensory inputs.

“Horses are prey animals, so it makes perfect sense that they would use any information available in their environment to warn them of potential threats,” she said.

“It is important to remember that horses do not rely on the ‘smell’ of fear from humans but, in the real world, will use all of their senses to make decisions about threat level,” Pearson added.

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