There's something in the air
There is definitely someone you "can't smell", and some perfume and deodorant manufacturers promise not only the scent of adventure and freedom, but also irresistible effects on the opposite sex. But it has only now been proven that not only animals but also humans communicate unconsciously via chemical substances in the air. There is definitive evidence for the existence of human pheromones -- this is the startling thesis put forward by Martha K. McClintock and Kathleen Stern of the University of Chicago in a March 12, 1998 report in Nature. As early as 1971, McClintock discovered that a group of women who lived together were more likely to have synchronized menstrual cycles than would be expected by chance. She concluded at the time that there is an "interpersonal physiological process that affects the menstrual cycle." She guessed it was a human pheromone, but that was just speculation.
According to Martha K. McClintock, "The public and many scientists believe that human pheromones exist. Both the media and numerous scientific texts make this assumption as if it were a fact. However, until now, never provided conclusive evidence of human pheromones."
The idea that humans could produce pheromones probably gained traction because it seemed the most plausible explanation for an effect many young women have noticed on themselves within their social groups or the university: the Synchronization of menstrual cycles. There is also a lot of evidence for chemical communication between animals, so why shouldn't humans do the same? Another clue was the discovery that in humans the vomeronasal organ - a structure that other mammals use to detect pheromones - is not an atrophied organ such as the appendix. This specialized structure, found near the nasal cavity, also shows gender differences.
However, proving that human pheromones really exist was not easy. Synchronized menstrual cycles could result from routine tasks performed together or from environmental cues. Even distinguishing whether the communication is through a scent or a pheromone, which by definition is not perceptible as an odor, was not straightforward.
Between the 1971 study and the current report, McClintock learned a lot about controlling reproductive cycles via pheromones from experiments with rodents. Through isolated female rats whose cages were connected by a common air supply, she found that there were two pheromones: one that lengthened the estrous cycle and one that shortened it (estrus is the period of sexual activity and readiness for copulation in many mammals).
Now McClintock and Stern have found evidence of a similar type of system in humans. They were able to identify pheromones that could not be smelled and described a mechanism by which the signaling substances can synchronize menstruation in different women.
The researchers collected women's body odors on cotton swabs and rubbed them on the upper lips of the women who were supposed to receive these odors. The procedure was repeated daily for the next two menstrual cycles. It turned out that the course of the cycle could actually be influenced systematically: Substances from the follicular phase accelerated the increase in luteinizing hormone and thus shortened the cycle duration. Substances from the same donors, obtained later during ovulation, delayed the release of hormones and thereby lengthened the menstrual cycle. As in rats, two pheromones appear to be involved in this process in humans.
The researchers attributed all changes caused by pheromones to the stages of the follicular phase or the ovulatory phase, while other periods of menstruation produced no regulatory substances.
Aron Weller of Bar-Ilan University in Israel says the study "demonstrates unequivocally for the first time that the potential for chemical communication involving sexual functions has been preserved in humans over the course of evolution." He believes the results open up new possibilities in contraception and the treatment of infertility. And he believes that "we may yet discover that other aspects of our behavior and physiology are influenced by other people's latent olfactory messages during social interaction".
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