They help moths to mate, locusts to swarm and ants to recognise each other. But what do pheromones do for humans? Are they the subliminal seducers the cosmetics industry would have us believe?
The idea that it is possible to spray on a substance that will make you irresistible to members of the opposite sex, or that you exude a natural perfume that has the same effect, is an intriguing theory which many scientists have investigated.
Natural chemicals which act in this way, known as pheromones, exist in the animal world. Pheromones are often described as ‘natural aphrodisiacs’ and they definitely operate to stimulate sexual interest. These chemical communicators are in fact special types of hormones which act externally, sometimes over long distances, to influence the behaviour of other members of the same species.
Pheromones are emitted in tiny quantities, but they can be picked up by the hypersensitive olfactory equipment of the creatures at which they are aimed. Whether humans are capable of detecting and producing similar sexual attractants has been open to question. Some scientists have said that humans do not secrete pheromones, the reason being that, unlike other animals, we do not need to. We have other means of signalling our sexual interest – by body language, eye contact and speech.
The role of smell
The sense of smell has had a much larger role to play in the sex lives of animals. There exists, however, a good deal of evidence that the sense of smell plays an important part in the sexual attraction of human beings.
This is why perfumes, scented soaps, colognes and after-shave lotions are so popular, especially in the west. They not only mask the less pleasant body odours; they also give out a subtle message of sexual availability.
Since artificial perfumes can act as sexual stimulants, are natural body odours in any way sexually arousing? It is sometimes argued that instead of savouring the body’s natural odours, the human nose has been conditioned to find these unacceptable.
We go to a great deal of trouble to destroy our own body odours by frequent washing. We suppress our natural smells with deodorants and antiperspirants and mask them with an array of colognes and perfumes, many of which contain substances such as muskone and civetone – the glandular secretions of the musk deer and the civet cat.
Despite our preoccupation with soaps and deodorants, it is probably true that our attraction to, and dislike of, another person is often based on smell. Women generally tend to notice whether a man smells right or wrong for them, and men tend to be attracted to a woman’s personal perfume. This is illustrated by Napoleon’s famous message to his wife, the Empress Josephine: ‘Will be home tonight. Don’t wash.’
Although scientists have not yet conclusively identified the roles pheromones play in human sexual behaviour, it seems this may be significant. Since a large proportion of the animal kingdom attracts mates, repels rivals or signals its sexual receptiveness through odours produced by hormones, it seems unlikely that we are an exception.
As one writer has pointed out, humans still have the necessary secretory glands for producing these substances, and it is extremely unlikely that as we evolved we lost our ability to secrete them. But it may be that through social pressures we are gradually becoming less able to recognise and respond to them.
The glands referred to are those in a woman’s vagina, those at the end of a man’s penis, and the apocrine glands in the armpits and skin of both sexes. All three of these areas emit odours, and two of them have direct sexual significance. The vaginal area is the region which is most likely to produce pheromones liable to influence the male’s sexual attraction, attitudes and behaviour. The prostitutes of mediaeval Naples are known to have dabbed their vaginal fluids behind their ears to encourage trade, but with what measure of success has not been recorded for posterity.
It has been found that if vaginal secretions were taken from female rhesus monkeys in heat, and applied to females who were not ovulating, the attitude of nearby males would change quite dramatically.
They would immediately attempt to have intercourse with the second group of females – even though they had previously ignored them. This suggested that there were some agents in the vaginal fluids which stimulate the males’ sexual interests. These fluids were termed ‘copulins’. When analyzed, these copulins were discovered to be a series of organic acids, which were also to be found in female vaginal secretions.
Scientists believe that the apocrine glands in the armpits and skin may be one source of human sex pheromones. These glands exude sweat, which is a source of androstenol, the likeliest substance so far to be identified as a human sex pheromone.
Androstenol is a steroid, chemically similar to the male sex hormone, testosterone. Both men and women secrete it in their sweat, including their auxiliary (or armpit) sweat.
But does androstenol smell attractive and does it have any sexual significance? In tests, not everyone could smell androstenol. Of the two thirds who could, some disliked it intensely, while others found it pleasant and musky.
Apart from the fact that it is chemically similar to testosterone, another reason for regarding androstenol as a human pheromone is that women are more sensitive to it at certain stages in the menstrual cycle when their oestrogen level is high, particularly around ovulation time. Interestingly, this is the time when they are most likely to have multiple orgasms either as a result of masturbation or intercourse.
Boar taint tests
A female pig sprayed with boar taint, the musky smell of male pig which also contains androstenol, will become sexually receptive, and assume a mating posture. For this reason, androstenol sprays are manufactured on a large scale for use by pig breeders.
Androstenol is also widely used in perfumes and soaps. The makers would have us believe that it has the same effect on women that it has on sows. Sprays containing androstenol can be bought in sex shops with the promise that it will attract women.
In another experiment, boar taint containing androstenol was used to mark some chairs in a dentist’s waiting room. The researcher watched to see who sat on the marked chairs and who avoided them. He found that women tended to choose the chairs with boar taint, whereas men tended to shun them. In this case it seemed that the pheromone attracted females rather than males – the opposite of the conclusions which were first assumed about androstenol.
Results of research into the effects of androstenol on humans have so far been somewhat unconvincing. But one effect of the chemical which has been demonstrated very clearly is its ability to produce menstrual synchrony.
Women who live together in a nurses’ home or student hall of residence tend eventually to menstruate at the same time. This tendency is the result of exposure to odours from body secretions. It can be produced by exposing women for a short while each day to nothing more than the smell of sweat from pads that were originally placed in the armpits of other women.
The women concerned do not even have to meet, let alone live with each other, for this effect to occur. But proving that androstenol is some form of sexual signal is much more difficult. You cannot simply spray it over someone and wait to see whether he or she becomes sexually aroused – the effect will be much less obvious than this.
It would appear from the results of all of these experiments that pheromones have a definite, though sometimes unpredictable effect on human sexual behaviour. Perhaps scents and odours will always retain some of their elusive and mysterious charm.