Pheromone Friday

Pheromones, emitted chemicals that elicit a social response in members of the same species, have been most widely studied in insects as a mode of communication. In the insect world, pheromones can signal alarm, mark trails, control worker bee behavior, and elicit sexual behavior.

Sex pheromones are the chemicals that come to mind in popular lore. Do human beings secrete substances that are likely to attract potential mates? Unscrupulous players in the fragrance industry would like you to believe that's the case. Unable to attract women (or men)? There's a difference between marketing an intoxicating and sensual fragrance that's pleasing to the nose and snake oil such as:

Amazon even cautions prospective customers about SexyLife.





{BTW, humans lack a functional vomeronasal organ, the part of the accessory olfactory system that detects pheromones / chemosignals / non-volatile molecules (Petrulis, 2013).}


Don't we already know that human pheromones are a crock?

It depends on how you define pheromone, some would say.¹ “In mammals [rodents], few definitive cases have been identified in which single pheromone compounds evoke robust sexual behaviours, which might reflect an important contribution of signature mixtures in sexual communication” (Gomez-Diaz & Benton 2013, The joy of sex pheromones). In rodents, reproductive responses to “odor blends” or chemosignals are heavily modulated by experience, as opposed to the instinctive and fixed behaviors elicited by pheromones in insects. The evidence supporting the existence of mammalian pheromones is so weak that Richard Doty has called it The Great Pheromone Myth.

If rats don't have “pheromones” per se, why look for them in humans? Tristram Wyatt, who believes that human pheromones probably exist, wrote a paper called The search for human pheromones: the lost decades. He criticized the literature on four androgen-related steroids (androstenone, androstenol, androstadienone and estratetraenol), saying it suffers from publication bias, small sample sizes, lack of replication, and commercial conflicts of interest. There is no bioassay-based evidence that these molecules are human pheromones, yet “the attraction of studies on androstadienone (AND) and/or estratetraenol (EST) seems unstoppable” (Wyatt, 2015).

{Curiously, the SexyLife ad accurately lists the putative male pheromones, although their depicted functions are pure fantasy.}

Unstoppable it is. Supporters of human pheromones have recently published positive results on male sexual cognition, male dominance perception, cross-cultural chemosignaling of emotions, and sex differences in the main olfactory system.²


Olfactory Attraction

On the other hand, a null finding from 2017 drew a lot of attention from popular media outlets and Science magazine, where the senior author stated: “I’ve convinced myself that AND and EST are not worth pursuing.” In that study, AND & EST had no effect on the participants' attractiveness ratings for photographs of opposite-sex faces (Hare et al., 2017).

The evolutionary basis of Smell Dating was given a cold shower by studies showing that the fresh (and odorless) armpit sweat of men and women, when incubated in vitro with bacteria that produce body odor, were rated identically on pleasantness and intensity (reviewed in Doty, 2014). Meanwhile, the day-old smelly armpit sweat of men was rated as equally unpleasant by men and women.³ Likewise, pleasantness and intensity ratings for female armpit sweat did not differ between men and women. This doesn't bode well for heterosexual dating...

Odors and fragrances are an important part of attraction, of course, but don't call them pheromones.


Footnotes

¹ There is an accepted definition for "pheromone".

² Since humans don't have an accessory olfactory system with its fun vomeronasal organ, the main olfactory system would have to do the pheromone-detecting work.

³ This could be due to larger apocrine glands, hairy armpits, and more carnivorous diets in men (Doty, 2014).


Further Reading

Scientific post in favor of human pheromones:

• On the Existence of Human Pheromones

“Whether one chooses to believe in the existence of human pheromones or not, steroids clearly serve an essential olfactory signaling function that impacts broadly ranging aspects of the human condition from gender perception to social behavior to dietary choices.”

PET studies on AND, EST, and sexual orientation:

• Sweat, Urine, and Sexual Orientation
• The PNAS Word

• Review of PET studies on AND & EST

References

Doty RL. (2014). Human Pheromones: Do They Exist? In: Mucignat-Caretta C, editor. Neurobiology of Chemical Communication. Boca Raton (FL): CRC Press/Taylor & Francis; Chapter 19.

Gomez-Diaz C, Benton R. (2013). The joy of sex pheromones. EMBO Rep. 14(10): 874-83.

Hare RM, Schlatter S, Rhodes G, Simmons LW. (2017). Putative sex-specific humanpheromones do not affect gender perception, attractiveness ratings orunfaithfulness judgements of opposite sex faces. R Soc Open Sci. 4(3):160831.

Petrulis A. (2013). Chemosignals, hormones and mammalian reproduction. Horm Behav. 63(5): 723-41.

Wyatt TD. (2015). The search for human pheromones: the lost decades and the necessity of returning to first principles. Proc Biol Sci. 282(1804):20142994.