Fear pheromones?

We’re used to the idea of animals communicating by odors. For instance, dogs and mice. But humans?

The idea isn’t a new one. Many years ago, there was a study claiming that college women in dormitories had synchronized menstrual cycles, and that the scent of one woman’s perspiration could re-program another’s cycle. I since read that that study couldn’t be replicated.

The present paper is new, and involves a relatively small study population, so time will tell if it holds up.

They took perspiration from the same individual after sky-diving (fear sweat) and after a routine workout (control). Cortisol was significantly higher in the skydiving group, indicating successful fear induction. 30 males study participants rated fear sweat as less pleasant, more intense and denoting higher fear than control sweat.

In preliminary studies, they worked out conditions where a “volatile bouquet” of sweat, below the level of perception, could elicit a pronounced autonomic response to the undetected smell of fear.

The most interesting part of the study used two identical-looking manikins, “Chris” and “Steve.” Each could deliver advice on solving computer-based tasks. One emitted undetectable fear body odor through its nostrils, while the other emitted undetectable control body odor. From the paper:

“Participants were told in advance that one manikin gives better hints, but they were not told which manikin it was. In reality, both manikins gave correct hints 70% of the time. After receiving the hint, the participant walked back to a standing-height monitor and used a mouse to direct a cursor and click on the target once it appeared, on the left or right of the screen. We hypothesized that increased trust in one of the manikins would materialize in reduced time-to-target for correct hints given by that manikin. This is because if one trusts the hint, one can move the cursor in the correct direction before the target appears. Notably, this is a genuinely double-blind experiment given that a manikin doesn’t know what odor it is emitting. “

In this experiment, subjects were 20 autism spectrum and 20 typically developed subjects. The typically developed subjects had a measured increased trust in the control-smell, while autism spectrum participants had a measured increased trust in the fear-smell manikin.

Again, from the paper:

“We conclude in reiterating that a series of experiments . . .  converge to paint a picture of dissociated autonomic and behavioral responses to undetected social chemosignals in ASD. This may give rise to a condition we term social dysosmia. We speculate that social dysosmia may underlie part of the impaired reading of emotional cues in ASD.”

In western society, with its emphasis on hygiene, widespread use of antiperspirant and high volume turnover air conditioning, I wonder how relevant this is in daily life. But I find the idea that subliminal odor cues could be relevant to human perception fascinating.

https://www.nature.com/articles/s41593-017-0024-x