Pheromones

The word pheromone is derived from the Greek words pherein (to transport) and hormone (to stimulate). [1] The term was coined by German scientists Peter Karlson and Martin Lüscher in 1959, although other scientists had already been researching the chemicals by that time. The first pheromone to be discovered / isolated was a substance found to be released by the female silkworm to attract mates. It was discovered by German biochemist Adolf Butenandt and was named bombykol. [4]

Pheromones in humans

The subject of whether humans use pheromones as sexual attractants has been a subject of great debate for many years. Although the use of sexual pheromones by several animal species has been demonstrated by research, the human world lacks concrete scientific 'hard proof'. Although many studies have shown connections between olfactory responses to certain substances and hormonal changes in the body, it is often stated that "no pheromonal substance has ever been demonstrated to directly influence human behavior in a peer reviewed study." [1]

The lack of 'proof' for the action of sexual pheromones in humans does not stop the sales of "pheromone sprays". Scented products claiming to contain human sexual pheromones which will give the user irresistible magnetism have been popular for many years.

Given the fact that many animal species use pheromones, it would seem surprising if humans were altogether different: A female dog goes into heat, and the males dogs within a wide radius will be drawn to the scent. Horse breeders using artificial insemination will use the scent of a mare in season to prepare the stud. There are numerous further examples. It is possible that humans use pheromones as attractants and / or as signals of genotype / compatibility - but due to the highly subjective and variable nature of human attraction and arousal, study has been more challenging than the study of other animals.

There have however been numerous scientific studies showing interesting results. One of the most famous of these was a 1998 study published in Nature, claiming to provide definite evidence of human pheromones. It showed that an odorless chemical produced by the armpits of women affected the preovulatory surge of luteinizing hormone, either shortening or lengthening their menstrual cycle to fall into accordance with the cycle of the 'donor'. [2] Many women believe that over time their cycle will fall into the same rhythm of other women with whom they share much proximity (i.e. roommates) and the study would seem to explain this. However, these results have been questioned by more recent studies. [5]

A 2002 study at the San Francisco State University showed that synthetic pheromones added to women's perfume increases the sexual attractiveness of women to men. It was concluded that the pheromones, which have no detectable smell, send a biological signal to a man that the woman can reproduce, to which he responds with romantic behavior. The abstract did not state the exact formula of the pheromones but stated that they were 'derived from earlier work investigating the underarm secretions of fertile, sexually active, heterosexual women'. [6]

Androstadienone and Androstenone

A 2007 study in the Journal of Neuroscience found that a single chemical, androstadienone (4,16-androstadien-3-one), found in human male sweat, increased levels of cortisol in women who smelled it. [7]

Studies have also found that androstadienone regulated the menstrual cycle of women who smelled them, increasing the release of luteinizing hormone, which stimulates ovulation. A further study found that androstadienone elevated the mood of women, but only when in the presence of males. [8]

Another substance of interest as a possible human pheromone is androstenone. Androstenone (5a-androst-16-en-3-one) is a steroid found in both male and female human sweat. It has been shown to be a pheromone in pigs: It is found in high concentration in the saliva of male pigs - and female pigs that are in heat and sniff the androstenone, assume the mating stance. [9]

Even more fascinating is a recent discovery that depending on genotype, androstenone and androstadienone will be perceived as pleasant or unpleasant by different individuals. Some would describe the smell as 'vanilla', others would describe it as 'stale urine' - and the difference in this perception was linked to the genetics of the individual. [10] This study would seem to suggest that attraction has become linked to genetic suitability by evolution, and that the pheromones play a role in triggering attraction to a compatible mate.

More fascinating yet is that androstenone is found in celery - another item suggested to be an aphrodisiac.

Androstenol

Androstenol is another sex pheromone found in pigs, which possesses a musk-like odor. It is also found in human sweat and is secreted by the adrenal gland in humans. [11] Here's where it gets interesting: A substance very similar to androstenol is found in truffles, which are thought by some to be an aphrodisiac. Truffles are hunted for by specially trained "truffle pigs" which are thought to hunt avidly for the truffles owing to the similarity of the scent to androstenol.

A 2010 study on heterosexual women has found that androstenol caused activation of a portion of the hypothalamus, a region of the brain not activated by other 'ordinary' odors. The hypothalamus, according to animal data, is responsible for mediation of mating behavior. [12] This study shows a possible sex pheromone activity for androstenol.

Estratetraenol

Estratetraenol is a chemical produced by women which has been described as having pheromone-like activities in primates, including humans. [13]

Further study has supported the idea of differentiated processing of androstenone and estratetraenol in connection with human attraction responses - even suggesting that gender preferences (hetero / homosexual orientation) may be linked directly to the processing of these chemicals by the brain, regardless of the gender of the scent recipient. [14]

Trimethylamine

In 1756 the Swedish botanist Linnaeus noted that dogs were very fond of the smell of the plant Chemopodium vulvaria. This plant was given its name on account of the similarity of its smell to that of human menstrual blood. The chemical responsible for both the smell of menstrual blood and the smell of the plant is trimethylamine. It has a characteristic smell described as "fishy". It is often agreed that the scent of human menstrual blood causes sexual excitement in several animal species, and it has been theorized that trimethylamine may be an estrus-signalling pheromone for animal species that have estrous cycles. [15]

Many mammalian species have estrous cycles - including dogs, horses, cats, rats, sheep, elephants, bears, foxes, wolves, hamsters, goats and pigs. Species that have estrous cycles (as opposed to menstrual cycles), are typically only sexually active at the time of fertility (ovulation), whereas species with menstrual cycles (such as humans) may be sexually active throughout the menstrual cycle. [16] Menstruation is less common, being limited to humans, close evolutionary relatives such as chimpanzees and a few other species - and humans are one of the only species in which ovulation is concealed. [17]

Vanilla and Pheromones

A further twist - it's widely quoted online that "The molecular structure of pure vanilla essential oil is similar in composition and structure to human pheromones and can intermingle with them easily." This quote appears on numerous web sites - however the source is not stated. Is it possible that there is a subtle connection between human sweat, pigs, truffles, celery, vanilla and other scent aphrodisiacs? We can only wait for science to catch up.

Tweet