Horses can smell humans’ fear and joy, study finds, and change their behaviour accordingly

Horses can smell humans’ fear, a study has found, and its scent and that of other emotions can influence horses’ behaviour.

Research published in scientific journal Plos One found that horses showed “significantly heightened” fear responses and reduced interaction with people when they were exposed to fear-related human odours.

“These results highlight the significance of chemosignals in interspecific interactions and provide insights into questions about the impact of domestication on emotional communication,” the researchers said. “Moreover, these findings have practical implications regarding the significance of handlers’ emotional states and its transmission through odours during human-horse interactions.”

The research team, led by Plotine Jardat, equine welfare and behaviour researcher at the Institut Français du Cheval et de l’Equitation, said that smell is the most common sense by which animals communicate, but human understanding of this is limited.

They cited previous work highlighting the role of sweat produced in human armpits in conveying information about emotional state to other people, and research indicating that dogs respond to human odours linked to fear and stress.

“Mice and cows also appear to discriminate human odours associated with different emotional states,” the researchers state. “But to date the role of olfaction in interspecific interactions remains insufficiently understood.

“The aim of the present study was to further explore the role of emotional olfactory signals in interspecific interactions, and more precisely in human-animal interactions.”

Recognising human expressions

Previous research has found that horses can recognise individual human faces from pictures, and remember them for at least six months, and that they can perceive our emotions, reacting differently to angry and happy expressions.

The researchers recruited 30 human volunteers, who watched horror and “joyful” films on separate days, each time with cotton pads in their armpits. The pads, and others that had not been exposed to any sweat, were held in front of the horses’ nostrils in different situations. The team observed their behaviour and measured their heart rate and levels of stress hormone cortisol in the saliva.

“More than just a reaction to odours, there appears to be an analogy between the emotional state of the donor (human) and that of the receiver (horse),” the researchers said. “Indeed, the observed responses indicate a shift towards a more negative and higher arousal emotional state in horses, consistent with the emotional valence and arousal of the human emitters.

“Our observations suggest that emotional contagion of fear through odours, previously observed among humans, could also occur interspecifically, although these results still need validation from independent studies.”

In conclusion, the researchers said they have shown that human emotional body odours can influence horses’ behaviour and physiology – that horses can smell humans’ fear.

“This highlights the significance of chemosignals in interspecific interactions and provides new insights into questions about the impact of domestication on emotional communication,” they said. “Practical implications include acknowledging the importance of handlers’ emotional state and its potential transmission through chemosignals during human-horse interactions.”

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