Can Animals Recognize Human Fear? A Study with Horses

There is an opinion that human emotions can be determined by the smell of sweat, but how true is this?

There is an opinion that, despite the fear of dogs, it is important to walk past them with complete confidence so that they do not pick up on your fear and do not show aggression. But what do scientific studies say about this?

For several years, scientists have been studying whether animals can recognize a person's state by smell. However, testing this in the presence of people turned out to be a challenging task, as dogs respond not only to smells but also to facial expressions, postures, and other factors. Therefore, in one of the experiments, they decided to exclude human presence.

In one recent study, the results of which were published in the journal Scientific Reports, participants were asked to watch comedies one day and horror films the next. After viewing, sweat samples were collected using cotton pads, and they were asked to rate their levels of joy and fear. Then, samples from the same person were offered to horses to test their ability to differentiate smells.

The researchers admitted that they initially doubted the horses' ability to differentiate smells; however, the results showed that they reacted differently depending on which sample was presented to them. In particular, when the horses sniffed the “joyful” samples, they used only their left nostril, while they sniffed the “fearful” sample with both nostrils and did so for a longer time. According to the scientists, this may indicate which part of the horse's brain is engaged in analyzing smells, although it does not necessarily mean that they understand what fear is.

The question remains open as to which specific chemical compounds produced by humans in sweat influence horse behavior. Scientists suggest that the horses' reactions may be driven by chemosignals—chemical substances that animals release and which can influence the behavior of others. Human sweat contains various compounds such as adrenaline and androstenedione, which can alter the scent in moments of fear. These compounds can convey “emotional information” between species.

In the future, researchers plan to determine whether the smell of fear can scare horses and what emotional impact it may have on the animals.

Similar experiments have previously been conducted on dogs. In these, people were also shown comedies and horrors, sweat samples were collected, and they were placed in a box, which was then taken to a room where a dog, its owner, and a stranger were present. The animals' reactions varied. For example, after sniffing the sweat of a person who had just watched a comedy, the dogs interacted calmly with the stranger. However, as soon as the “horror sample” was in the box, the dogs began to cling to their owners or sought to leave the room.