Can We Smell Human Emotions?

Most people assume that animals have powers of smell that are far superior to our own as humans. And many of those people assume that included in the things that animals can smell are emotions, either the emotions of other animals or of humans. We even have sayings about this, such as warning a person reacting strongly to a barking dog that “He can smell fear on you.”

As it turns out, these assumptions are correct; scientists have long been aware of the role that chemosignals play in animal communication. Many animals have been shown to use smells to communicate danger to other animals. In insects, for example, in response to danger or stress ants produce a chemosignal that warns other ants and summons them to help, or use other scents to mark trails to a food source. In mammals, certain scents are used as primer pheromones to trigger changes in the endocrine systems of other animals. For example, many species release pheromones that trigger sexual urges in prospective mates; in rats there is even a scent released by male rats that causes young female rats in the vicinity to mature more quickly. And of course every dog owner knows the phenomenon of “doggie email,” in which dogs sniff the urine of other dogs to determine whether they are dominant “alpha dogs” or not, and to assess their general level of health.

But it’s generally been assumed that humans lost the olfactory ability to do this long ago, and that our noses just aren’t sensitive enough to perceive smells on this level, and extract useful information from them. Well, a new study from the Netherlands just published in the journal Psychological Science indicates that this assumption is not correct.

The smell of fear is not only detectable by humans, it’s communicable

To test whether humans can also detect certain emotions in other humans – just from the chemosignals in their body odors – researchers at Utrecht University recruited a number of men and women volunteers and had them “prepare” for the experiments by refraining from “smell contamination” for several days. They were instructed to abstain from smoking, from eating smelly foods, from drinking alcohol (which affects not only one’s body odor but one’s sense of smell), from over-exercising, and were further asked to use only odor-free soaps and shampoos provided to them by the researchers.

Then they had the male volunteers watch a series of movies or movie clips, which had been selected to evoke either fear or disgust, and collected samples of their armpit sweat as they reacted. For example, as the men watched particularly frightening scenes from the Stephen King horror movie “The Shining,” the researchers collected samples of “fear smell.” Or as the men watched particularly repulsive clips from the MTV series “Jackass,” they collected samples of “disgust smell.”

They then asked the 36 female volunteers (chosen because past research has shown that women are more sensitive to men’s smells than vice versa) to sniff a series of odors, among which were the “fear smell” and “disgust smell” samples, interspersed at random. The researchers monitored the women’s expressions and reactions, and found that when they inhaled the “fear smell,” they opened their eyes wide and displayed a scared expression. Similarly, when the women inhaled the “disgust smells,” they scrunched their faces into a repulsed grimace.

So humans really can smell fear and disgust

The researchers concluded from their experiments that humans can indeed detect some emotions just from the smell they produce in the body odors of other humans, and that these emotions are to some extent communicable, in that they can be transmitted to others as information that they then react to in kind. This has many ramifications, not least upon the issue of fear or other emotions spreading through crowds. As the authors wrote in their study, “Our research suggests that emotional chemosignals can be potential contributors to emotional contagion in situations involving dense crowds.” They also commented, “These findings are contrary to the commonly accepted assumption that human communication runs exclusively via language or visual channels.”

Such findings are not unique. A previous study conducted at Rice University in 2010 found that people in close romantic relationships could smell emotions such as happiness, fear, and sexual arousal in their partners. As one of the researchers in that study put it, “Familiarity with a partner enhances detection of emotional cues in that person’s smell.”

As for what this all means, and how to put it to productive use, that will be determined by follow-up research, and by scientists in the future. But for now, you can use the information as a kind of general guideline. For example, the next time you walk into a crowded nightclub and stop, sensing somehow that you smell “fear in the air,” you might want to pay attention and go to another club. You might just be right.

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