French ethologists have discovered that horses are capable of detecting a person's emotional state using only their sense of smell. Experiments showed that the scent of sweat from frightened people causes anxiety in horses, making them startle more frequently and avoid physical contact.

Emotional Contagion in Animals

In biology, there is a hypothesis known as emotional contagion—the ability of animals to pick up on the emotional states of those around them. It is well established that within a single species, this mechanism works through chemical signals: if one individual becomes frightened and releases pheromones, fear quickly spreads throughout the group.

Inter-species Perception of Emotions

This raises the question: can this ancient mechanism function between different species, for example, between humans and horses? For horses, as prey animals whose survival depends on quick flight, the ability to sense a companion's fear in advance could be an evolutionary advantage. Researchers set out to test whether horses can perceive "alarm signals" from humans solely through scent, without any visual or auditory cues.

The Experiment

The study involved 43 Welsh mares. To collect scent samples, 30 volunteers watched videos designed to evoke strong emotions: horror films to produce a "fear scent" and comedies for a "joy scent." Sweat was collected on cotton pads that participants held under their arms.

The horses were then fitted with special masks containing these pads. The animals were divided into groups: some inhaled the scent of fear, others the scent of joy, and a third group received a neutral control sample (clean pads). In this state, the horses underwent a series of behavioral tests: an umbrella was suddenly opened near them, an unfamiliar object was placed in their enclosure, or they were invited to approach a person for petting.

Study Results

Behavioral analysis showed that the scent of fear had an immediate impact on the horses' state. Horses exposed to samples from frightened people reacted much more sharply to external stimuli: they startled more strongly when the umbrella was opened unexpectedly, and their heart rates rose higher than those in the control group.

Their social behavior also changed: under the influence of the "chemical danger signal," the animals became more cautious, spent more time anxiously examining unfamiliar objects, and were less likely to approach people, preferring to keep their distance. Notably, the scent of joy did not cause significant behavioral changes—their reactions were almost identical to those with neutral samples.

Practical Significance of the Discovery

This study supports the hypothesis of interspecies emotional contagion through scent. The discovery has important practical implications for horseback riding and hippotherapy: if a rider or caretaker feels fear, the horse can pick up this chemical signal and become more nervous, which directly affects the safety of their interaction.