Can animals smell human fear?

Research shows that dogs and horses respond differently to scent samples collected from fearful and happy people.

In the study, horses' behavior changed depending on the scent humans emitted when they were scared or happy. Photo: iStock — In the study, horses' behavior changed depending on the scent humans emitted when they were scared or happy. Photo: *iStock*

Can animals smell fear? To find the root answer, researchers removed humans from the experiment, since animals like dogs respond to human expressions and body posture. Instead, they focused on how animals, including horses and dogs, responded to the different odors that humans emitted when watching funny and scary videos .

In a study with horses, published in the journal Scientific Reports in 2023, the team showed volunteers a comedy video one day and a horror movie the next. After each session, the team used cotton swabs to collect sweat samples from the volunteers’ armpits and asked them to report how happy or scared they felt while watching each video.

Next, the team presented two cotton swabs from the same volunteer to the horses to see if they could distinguish between the scents released during happy and fearful moments. They found that the horses responded differently depending on which swab was provided.

"When smelling the happy samples, the horses only used their left nostril. This revealed which part of the brain they were using to analyze the smell. In all mammals, the two hemispheres of the brain have different functions and, in terms of emotions, it seems that smells from happy samples were perceived as positive by horses," said Plotine Jardat, a PhD student at the University of Tours and lead author of the study.

In the samples collected after volunteers watched the horror film, horses responded differently. Not only did they sniff the sample for longer, but they also used both nostrils. However, Jardat says this doesn’t necessarily mean that horses understand fear. “When horses sniff another animal, it’s not like the word ‘fear’ comes to mind. But we know that horses can distinguish smells from different emotional states in people,” she explains.

So what is it in human sweat that causes horses to change their behavior? The researchers suggest that chemical signaling—chemicals that animals release that influence the behavior of other animals—might be responsible. In humans, certain compounds in sweat, such as adrenaline or androstadienone (a pheromone-like protein), can cause a change in odor when people are afraid. These compounds may also transmit “emotional information” from one species to another.

Dogs have different reactions to the smell of scared and happy people. Photo: Momtastic — Dogs have different reactions to the smell of scared and happy people. Photo: *Momtastic*

In a 2018 study published in the journal Animal Cognition , scientists had Labrador retrievers sniff samples from the armpits of male volunteers after they watched either a scary or a happy video. The researchers placed the samples in an open box and placed the box in a closed room with two people: the dog’s owner and a stranger.

Similar to the horse study, they found that dogs responded differently depending on whether they smelled a fearful or happy person. “When they smelled a happy person, they increased their interaction with the stranger in the room,” said Biagio D’Aniello, lead author of the study and professor of zoology at the University of Naples Federico II.

But when sniffing samples from fearful humans, the dogs reacted differently. “When they smell fear, they go to their owners or go to the door and try to escape the room,” says Anna Scandurra, a postdoctoral fellow at the University of Naples Federico II and co-author of the study.

Ultimately, the scientists concluded the same thing as the horse team: The dogs' reactions were likely due to chemical signaling, suggesting "interspecies emotional communication" was taking place.

Thu Thao (According to Live Science )

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