Can Humans Smell Fear?
You have probably heard the saying, “They can smell fear,” especially when talking about animals like dogs. But can humans also smell fear? We will examine this question by looking at a study titled “The Lasting Smell of Emotions: The Effects of Reutilizing Fear Sweat Samples.” [1].
The Science Behind Sweat and Emotions
Researchers know that body odours can reveal age, gender, health, and even how closely related people are [1]. Interestingly, our sweat may also carry chemical signals tied to our emotions [1]. These subtle messages might not be picked up consciously; however, our brain recognises these signals and still responds by sometimes copying the emotion we have “sensed” in others [1].
The Experiment
To test whether people can smell fear, researchers collected sweat samples from eight healthy men aged 21-35 years [1]. They collected sweat in two different emotional states: fear and neutral (calm) [1]. Each session was taken a week apart [1].
Participants watched horror movie clips to induce fear and calming nature scenes for the neutral condition [1]. Each session lasted 30 minutes [1].
To keep the sweat samples from being contaminated, participants had to follow strict rules for 48 hours before the experiment [1].
· No perfumes, deodorants, or any other body care products [1].
· No spicy or strong-smelling foods (like onion, garlic, and pepper) [1].
· No alcohol [1].
· No sex [1].
· No excessive exercise [1].
· No sleeping in the same bed as a partner or pet [1].
Participants were also asked to shave their armpits before the experiment and could only use scent-free body care products provided by the researchers [1]. Just before the experiment, they could only consume water [1]. In addition, they washed and dried their armpits before wearing clean clothes provided by the researchers [1].
Sweat Collection and Testing
They watched the videos [1]. To keep the conditions consistent, the temperature-controlled room was set at the same range for every session [1]. This ensures that temperature does not affect the amount of sweat or odour produced.
The sweat samples were later frozen and tested on 60 women aged 19-35 [1]. These women sniffed the samples while researchers tracked their facial muscle reactions using a technique called fEMG (facial electromyography) [1], which detects muscle activity. The specifically observed muscles are associated with emotional expression.
· The left corrugator supercilii [1] (a muscle near the eyebrows) and
· Medial frontalis [1] (located on the forehead).
Researchers chose men as sweat donors because they produce more sweat, making them better for sample collection [1]. In addition, women were chosen as sweat receivers because research suggests they have a better sense of smell and are more sensitive to emotional cues [1].
The Findings
What did they find?
· Stronger reactions to fear sweat: Women showed more pronounced facial reactions associated with fear when smelling the “fear sweat” compared to the neutral sweat [1].
· They couldn’t tell the difference by smell: The female participants couldn’t consciously tell the difference between fear and neutral sweat based on smell. They rated both as equally intense and pleasant (or unpleasant) [1].
· But their bodies knew: Despite not consciously knowing which sweat was fear-induced, their facial muscles reacted to the fear-based sweat [1]. This suggests that we can subconsciously pick up emotional signals from sweat.
· Neutral sweat made people feel happier: Participants reported an increased feeling of happiness when smelling the neutral sweat compared to the fear-based sweat [1].
· Fearful participants sweated more: During the fear sessions, participants produced around 20 milligrammes more sweat than in the neutral condition [1]. We know this isn’t based on temperature because the room temperature was the same for all groups.
What Does This Mean?
These findings suggest that fear does have a smell, but it’s not something we consciously detect [1]. Instead, our brains may pick up on chemical cues, causing us to respond emotionally without even realising it [1].
The paper does admit that the way we may sense emotions, such as fear, may differ in an everyday scenario. This is due to other sensory factors potentially affecting how the sweat smell is transmitted, such as wind and airflow [1]. Another question is whether men also have similar reactions when sniffing fear-induced sweat from women. This would be interesting because men generally have worse senses than women. However, it is still clear that sweat, particularly fear-induced sweat, does have a scent.
So, Can Humans Smell Fear?
So, can humans smell fear? The answer is yes, just not in the way we expect. It is a fascinating insight into how much information we constantly exchange with each other without even knowing it.
References
Reference paper “The lasting smell of emotions: The effects of reutilizing fear sweat samples”