In the course of human history, many have searched for substances and procedures to enhance their reproductive potential. One strategy has been to augment one’s libido via consumption of aphrodisiacs, which include champagne, oysters, “Spanish fly”, etc. More recently, the scientific community has contributed in advancing the cause with drugs such as Viagra, Cialis, and Levitrol, all of which improve sexual performance.
Another approach to expanding one’s mating potential is to increase the chances of
attracting those whom one desires. In such context, aphrodisiacs are virtually useless. While it is possible for one to slip into his unsuspecting dinner companion’s drink a dash of a strong aphrodisiac, to transform her or him into a horny wood nymph, such methods of seduction have three drawbacks. First, convincing another of becoming the dinner companion is usually more difficult than seducing someone who already has accepted the dinner invitation. Second, it may gnaw at one’s conscience. Third, such seductive methods have not proven to be practical because the alleged aphrodisiac may derive its potency from being a placebo and thus lose its putative powers upon administration. Additionally, the “victim” may eventually discover the low-handed maneuver and put to rest all romantic possibilities. Finally, the victim may become so aroused that she may run from the dinner table, only to avail herself to one of her ex-boyfriends. In summary, the use of aphrodisiacs does not seem apropos for the purpose of attracting a mate.
Currently, the most popular methods for becoming attractive include: becoming rich or socially influential, visiting a local plastic surgeon, dressing in fashionable clothes and make-up, and/or working out religiously. Unfortunately, each of the preceding activities requires much effort, risk, or luck. For example, ownership of great wealth or high status can render men more attractive, but its acquisition generally requires either an extraordinary amount of effort or luck. A local plastic surgeon can assist Joe Donut in improving his appearance, but the patient must incur significant risk, pain, and cost.
Perhaps, in the context of Darwinian evolution, it is only fair that those who are willing to entertain hardship or to incur risk can legitimize claims to mating privileges. Human nature being what it is however, resents such fairness. It seeks short cuts. It searches for paths to render oneself more attractive, to give oneself advantage over his or her competitors. It fantasizes about magical substances that will reduce the amount of work necessary in finding an attractive mate.
And so too do we search for something called human pheromone, which promise with all sincerity that one bathed in its ‘scents’ will be instantly transformed into Casanova or Venus.
Is there any validity to the claim that pheromones can act as an attractant? One famous “experiment” which attempted to answer the preceding question involved two pairs of twins—one pair consisting of males and other pair females. ABC News  conducted the experiment using the following procedure: one member of each pair wore an alleged pheromone and other member of each pair, a placebo. Next, each of the twins took turns standing at a noticeable location in a club. After a couple of hours, each experimental subject tallied the number of times he or she was approached by club patrons. The experiment showed that (1) the male pheromone wearer was approached approximately the same number of times as the male wearing a placebo; and that (2) the female pheromone wearer was approached a far greater number of times than her sister who wore the placebo. In summary, for one of the twin sisters at least, the substance claimed as pheromone seemed to have increased her attractiveness.
While the above “experiment” raises intriguing possibilities, unfortunately, it also exposes problems with non-scientific investigative approach. Simply put, the ABC News piece contained too many holes to serve as a reliable basis for concluding the existence of human pheromones. Firstly, as an “experiment,” it failed to provide statistical significance. Secondly, it failed to account for various psychological issues that could arise for the twins. For instance, it was never clear if the psychological states of the subjects were changing as the experiment progressed, depending on how many times they were approached. Such mood change could have altered their behavior, which in turn might have subtly augmented their attractiveness beyond the level afforded by the pheromone alone. Thirdly, other independent researchers would not be able to reproduce the results of the experiment, because the pheromone ingredients were kept secret.
To have a better understanding of pheromones, rather than putting a premium in sensationalist journalism like that detailed above, it makes more sense to carefully examine the landmark papers that enjoy high status as scientific publication. To set the stage, it is helpful to begin the traversal with the definition of “pheromone” and cover in broad strokes the brief history of pheromones.
To start, what are pheromones exactly? Surprisingly, “pheromones” are not something specifically related to sex or reproduction. The term designates a chemical substance that, when secreted by an organism, sends information to other members of the same specie. The broad definition has proven, coincidentally, consistent with many later experiments.
Early recorded research studies on pheromones, conducted during the late 19th and early 20th century, involved chemicals emitted by female moths for attracting males. Other early studies that were to follow generally investigated insects. And, those studies decisively showed that males of one insect species were attracted to a particular chemical emitted by the females of the same species. As one might imagine, the studies were conducted for formulating effective insecticides.
Subsequently, researchers shifted their attention from insects to mammals. One unfortunate species that received much torture in the name of science was the boar. The contemporaneous papers on boars generally mentioned the following phenomenon: estrous sows immediately assumed the mating stance upon detection of androstenone, a chemical substance found in the saliva of male boars. Subsequent studies examining androstenone’s general effects in detail reported similar findings: having detected androstenone, estrous sows exhibited physiological and behavioral changes.
Predictably, human pheromone studies followed. Many researchers began to apply androstenone and other related molecules to human subjects. In effect, a few of the scientists were attempting to arouse and attract women using boar pheromones. The research results were contradictory and confusing.
The studies did manage to produce a number of useful results. The human research studies were able to identify five steroid derivatives as potential human pheromones. They are: androstenone, estratetraenol, androstadienone, andrestenol and androsterone. Currently, while the five candidate pheromones do seem to affect human social behavior in some way, their true roles as pheromones are not clear. Each of these pheromones, along with androstenone, is discussed below.
Since its first discovery in male boar saliva, androstenone has also been found in human urine samples. Androstenone is noteworthy, despite the dearth of respectable human studies, because of its widespread reputation in the Internet as the human female attractant.
Many Internet sources cite experiments involving choice tests, in which a particular item of use is sprayed with androstenone. The women subjects are then asked to use or choose among a number of identical objects (e.g., chairs, photographs). According to the sources, the female subjects favor those objects sprayed with androstenone, while male subjects disfavor them. Despite the extravagant stories however, the sources generally fail to support their claims.
Among many Pubmed publications, only two by Thorne et al.  and Fislinger et al.  mention androstenone’s efficacy in modifying one’s social behavior. In Thorne et al.’s study, women were asked to rate the desirability of male photographs while they were exposed to androstenone . The study concluded that androstenone could increase the level of male attractiveness. It also conveniently explained away any anomalies by noting how menstrual cycles modulate women’s decisions.
In Fislinger et al.’s experiment, male and female subjects took several psychological tests during their exposure to androstenone . The males were asked to rate photographs of other men, while women were asked to rate fellow women. The men characterized the photographed males as being more passive, and the women rated themselves as less attractive than the control groups (i.e., those not exposed to androstenone). The study seemed to hint that androstenone functions as a “leadership” pheromone. However, the hint probably was not warranted, because no one really knows the effects of such pheromone. Perhaps the male subjects should have regarded the photographed men as more aggressive, since the subjects were not the source of androstenone.
Even though the studies support the view that androstenone exerts its effect on women as an attractant pheromone, it is not entirely clear whether their views are fully justified.
Androstenol (5-alpha-androst-16-en-3 alpha-ol)
Androstenol is probably the second most significant pheromone candidate. Benton et al. , Gustavson et al. , and Cowley et al.  studied its effect on social behavior. Benton et al.’s study attempted to correlate the degree of sexual arousal in women, who were asked to read erotic material, with the presence of androstenol. The study concluded that androstenol did not directly affect women’s arousal levels.
Gustavson et al. showed that androstenol exerts its influence in a choice test. Specifically, it demonstrated that men avoided restroom stalls sprayed with androstenol. Cowley et al. studied the non-sexual effects of androstenol on women. In its presence, women exhibited increased social interaction with men.
As a whole, the experiments reveal that androstenol, while it probably does not affect women’s desire, leads to two different consequences in men and women. Its presence apparently guides men to curtail male-to-male interaction, while it induces women to become more open and receptive to males.
Among the purported pheromones, there is not much credible information about androsterone.
Androstadienone (delta 4,16-androstadien-3-one) and estratetraenol (estra-1,3,5(10),16-tetraen-3-ol)
Androstadienone and estrtetraenol are special among pheromones, because they are associated with vomeronasal organ (VNO), which had been first designated by scientists as the mammalian pheromone detection system. In rats at least, the VNO proved to serve as a pheromone detector.
As it turns out, the VNO in humans, which had long been thought to be non-existent or had atrophied, was found to respond to androstadienone and estratetranol , . In fact, androstadienone and estratetraenol are the only two purported pheromones that have been shown to activate the VNO; androsterone, androstenone and androstenol do not trigger the human VNO. It should be noted that androstadienone and estratetraenol are gender-specific. That is, androstadienone stimulates only the male VNO and conversely for estratetraenol.
It would seem conclusive from the above that androstadienone and estratetraenol are the human pheromones. However, it is no longer clear if the mammalian pheromone detection system consists only of the VNO. For example, Dorries et al.  were able to prove that androstenone, even in estrous female pigs who’s VNO cannot relay proper signals to their brains, exerts its effects and readies them for mating.
Nonetheless, androstadienone still enjoys a special status among pheromones, because many studies related to the compound seem especially trustworthy. Jacobs et al.  and Lundstrom et al.  both have demonstrated androstadienone’s psychological effects. Specifically, in the presence of androstadienone, women are able to concentrate better and carry on their activities without deterioration in their moods, independent of menstrual cycle phases.
Jacobs et al. further demonstrated physiological responses in the presence of androstadienone . When the VNO detects androstadienone, it causes increased cerebral glucose utilization both in subcortical regions and in the neocortex, which are not exclusively associated with olfaction. These widely distributed changes are consistent with modulation in emotional states.
Gulyas et al. conducted the most recent and noteworthy androstadienone study. They employed positron emission tomography (PET) to measure brain blood flow changes in subjects who were exposed to androstadienone. The increased blood flows in specific areas of the brain were consistent with what Jacobs et al. were able to demonstrate.
In the original insect experiments, scientists discovered one pheromone for each insect species. However, in humans, finding the sex pheromones (one for males and another for females) has proven elusive. Simply put, multiple chemicals seem to be at work, with each chemical affecting some aspect of human social behavior.
There seem to be three general theories at this point: (1) the real sex pheromones have not yet been discovered (2) sexual attraction is the result of smaller subunits of behavior and thus can only be assembled by the use of multiple pheromones, each of which affect its own behavioral subunit and (3) sexual attraction is the result of specific social conditions, which can never be fully simulated by pheromones, and therefore, “sex attractants” do not exist.
For the purpose of this article, there is little to discuss regarding the first theory, because the instant article is a review and does not describe a bleeding-edge experimental study. It suffices to note that, while there is a good chance that the sex pheromones have not yet been discovered, it should not come as surprise if the opposite were true. That is, if the second and the third theories were plausible.
The second theory describes the situation in which there is no single sex attractant for each gender. The human pheromone system may be more complicated than those of insects; it suggests that many biochemicals may be involved in controlling and guiding human behavior. This is not so strange when one considers that the more advanced a species is in the evolutionary ladder, the more complicated its communication media. Given that human verbal and visual communication modes betray more complicated schemes than those of many other species, it should not come as a surprise if human pheromone systems also reveal greater complexity, with multiple pheromones acting in concert to elicit a particular set of actions.
The third theory takes the position that there is a limit on what pheromones can do and that their powers are compromised by human social dependence. Again, the proposal should not strike one as far-fetched. It is not too difficult to see that the behavior of creatures at high rungs of the evolutionary ladder depends more on social context than those at lower ones. For example, wolves exhibit far greater situation-dependent behavior than ants. The human ability to cope with different social situations implies its ability to override and handle immediate stimuli, including those fueled by pheromones.
The current review has made a cursory examination of the following: (1) purposes behind pheromone studies (2) pheromone history and (3) a number of significant human research studies on candidate pheromones, including androstenone, andrestenol, androsterone, androstadienone and estratetraenol.
Part II of this series will lightly sketch human sexual protocol as a subcomponent of broader social behavior. It will then attempt to explain how androstenone, androstenol, androstadienone and estratetraenol may perhaps serve social functions and thus, indirectly, facilitate human reproduction. It will also briefly revisit the possibility that the pair of real pheromones for attracting men and women have not yet been identified.
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