Many animal species have a highly developed sense of smell, capable of detecting chemical signals that indicate when a person is afraid.
For a long time, many have been curious about whether animals can sense human fear. However, obtaining a definitive answer is not straightforward.
So, can animals truly smell fear?
Scientists have investigated whether dogs can detect the scent of fear in humans. (Photo: Chalabala/Getty Images).
To find the answer, researchers ensured that the animals involved in the experiments did not see humans, as certain species, such as dogs, can interpret human body language and expressions. Instead, they focused on studying the animals’ reactions, including those of dogs and horses, to various scents emitted by humans while watching either cheerful or scary video clips.
In a study conducted on horses, published in 2023 in the journal Scientific Reports, researchers had volunteers watch comedic content one day and horror films the next.
They then collected sweat samples from the participants along with a questionnaire assessing the level of joy or fear they felt while watching. Next, the scientists allowed the test horses to smell the sweat samples to determine if they could distinguish between the scents associated with human happiness and fear.
The lead author of the study, PhD candidate Plotine Jardat from the University of Tours, France, stated: “Initially, we were unsure whether the horses could differentiate between the two scents, but they exhibited different reactions based on the sweat samples they smelled. When the horses sniffed the sweat from happy individuals, they only used their left nostril.
This indicates which part of the brain they use to analyze that scent. In all animals, the two hemispheres of the brain have different functions, and in emotional situations, it seems that the scent of happy sweat is perceived by the horses as a positive odor. However, when they smelled the sweat from those who watched horror films, their response was markedly different; they not only inhaled the sample longer but also used both nostrils to sense it.”
Nevertheless, Jardat also noted that this does not mean the horses understand what “fear” is.
“It’s not that when they smell another species’ scent, the word ‘fear’ pops into their heads, but now we know for sure that horses can distinguish the scents produced when humans are in different emotional states,” Plotine Jardat shared.
This raises the question: “What specific compounds does the human body produce through sweat that causes horses to change their behavior?”
The researchers suggest that chemical signals, which are chemicals produced by animals that can influence the behavior of other animals, are the reason behind the horses’ reactions.
In humans, certain compounds in sweat, such as adrenaline or androstadienone, can alter the scent when a person is afraid. These compounds may also carry “emotional information” from one species to another.
Another study conducted with dogs was published in the journal Animal Cognition in 2018.
In this study, scientists had Labrador retrievers smell sweat samples from men after they watched cheerful or scary video clips. They placed the sweat samples in an open box and set the box in a closed room with two people: one stranger and one dog owner. Similar to the horses in the previous study, these retrievers reacted differently based on the scent of the sweat from fearful or happy individuals.
The head of the study, Professor of Zoology Biagio D’Aniello at the University of Naples Federico II, Italy, noted that when dogs smelled the scent of a happy person, they increased their interactions with the stranger in the room. However, when they detected the scent of a fearful person, they reacted entirely differently, approaching their owner or heading toward the door in an attempt to leave the room.
Researchers at the University of Naples Federico II also concluded similarly to those at the University of Tours, that the dogs’ responses could be attributed to chemical signals, indicating that emotional communication between species is indeed real.
