by AbdesSalaam Attar

Part 4

Human pheromones

1. What are pheromones?

2. State of the research on pheromones

3. Sexual pheromones

4. Human pheromones

Human sense of smell and pheromones
The small size of our olfactory bulb does not mean that for us, micro osmic beings, the olfactory sense is less important that it is for animals better equipped (macro osmic), because we decipher olfactory  messages also from regions of the brain that do not exist in other mammals.

Chemical communication (olfactory) has a lot of relevance in various area of human behavior: In fact our body smell reflects our physiological state and inner metabolism, our diet, our sex gender and reproductive phase, and our health (diseases makes us produce characteristic smells).

These chemical (smelling) clues are often those that determine our social choices of frequentation and above all our mating choices (choice of the partner).

In the same optic, olfactory recognition of our own family members is of utter  importance in our social and reproductive behaviors; incest is not only a social taboo, it is an olfactory  biological one as well. For all mammals the odor of the near relatives is inhibitory of the reproductive function.

This “family” smell results from the production of body smells (pheromones) controlled by the MHC gene.
This gene makes everyone of us a produce a personal scent that communicates to others of the specy the immune patrimony that we have genetically inherited (see report N° 2).
The control that this smell exercises on our behavior is so powerful that it is really astonishing, because reflecting on the human tendency to systematical smash all taboos, only the existence of this olfactory  taboo can explain that incest is so little spread.

The existence in the human being of an active secondary olfactory organ, whose role is to recognize pheromones , the vomeronasal organ, is still contested. It is to be noticed though, that a pharmaceutical company pretends to have discovered a new therapy through this organ, and produces drugs to be inhaled, based on molecules of their patent called Vomeropherines

Olfactory preferences 

In human beings as in other animals, many olfactory preferences are the fruit of personal experience but there probably exists also some innate predispositions that are the fruit of a genetic olfactory inheritance.
This can be seen by observing the facial expressions of new born babies which are made to smell various test odors.

Moreover, the state of health and the state of mind of the persons provokes changes in their appreciation of smell. The smells of heavy foods will delight a hungry man but will give nausea to one afflicted by headache or fever.
In the case of pheromones, being perfumer, I have noticed the rather widespread existence a phenomenon known as “specific anosmy”. Some persons difficultly perceive the scent of Musks (men) and of Ambergris (women).

It has been shown that anosmy (absence of olfactory perception) specific to certain human corporeal smells is developed in the males (for androstenone) after the age of puberty, while the perception of the same molecule becomes more acute after this age in females.
Specific anosmy  assesses the incapacity to smell an aromatic molecule in the dilutions in which it is normally perceived, but does not assess the absence of “prime effect” (effect on the endocrine system), on these very persons. If on the contrary specific anosmy to certain pheromones was accompanied by the absence of prime effect, their anosmy would be a way for these persons to protect their organism when the stimulus provoked could be harmful to them.
Peoples reactions to these particular pheromones (acid metyl-exenoic, ethylheptanoico acid etc), just like the reaction to natural pheromones of perfumery (Civet, castoreum etc) can be either of real liking or of deep disgust, without half way through. Strangely the same products disliked by most (civet, Castoreum) render all perfumes that contain them more attractive than those without to the general public.

Axillary (armpit) smell in humans, being pheromones, provoke on others physiological effects (prime effects), that are visceral and little compatible with social interactions of civilized life, which are situated more on the mental level than on the physical one.
Therefore, body smells are judged negatively. This judgment is acquired with the time by the persons, when they grow assimilating the patrimony of their cultural values, by personal experience when reaching the age (with puberty) of being affected by the physiological effects of other people’s pheromones (and also to influence the others with their own), and lastly by reaching a stage in life in which the other people’s judgment becomes of utmost importance for the proper survival (sentimental and professional life).

The use of perfumes is common to all civilizations and can be traced in part to the need to eliminate the body smells (all natural aromatic molecules are bactericidal) in order to lead a civilized social life, but also in the desire to “spiritualize” one’s own individual smell. Our primary pheromone (axillary) smell remain anyway with the use of perfumes, but it is not perceived negatively because it is the degradation of the prime pheromones caused by the bacteria of the skin that produces the typical armpit scent.
The other instrument to reduce body smells common to many traditional civilizations is axillary and circumgenita depilation, still practiced in all Africa and all over the Muslim world, as well as in the Jewish culture
Effects of pheromones

Everybody’s personal experience is sufficient to make him understand that smells is extremely important for humans in their sexual choices and social exchanges. Scientific research tries to understand in which way they act on us.

It has been demonstrated as early as 1971 that women who live in group for some months, in certain circumstances synchronize their menstrual cycle under the infuence of the pheromones produced by the axillary glands.
An experiment in 1986 done with axillary secretions of males, placed on the upper lip of women, demonstrated that they were able to regulate the menstrual cycles of those women who had it either too long or too short, bringing it back into the 28 days of normality.
An experiment in 1990 showed also that girls exposed to daily physical contacts with relatives males delayed their puberty while physical exposure with unrelated males (stepfather for instance) had the opposite effect.
These and other experiments have demonstrated that smells produced by other persons have significant effects on human neuro endocrine processes.
These effects are called “prime effects”. All gland secretions are controlled by the endocrine system which is itself affected by smells through the nose, responding therefore to certain smells ordering the production of others, giving place to an olfactory conversation between people in a archetypal  chemical language.
But this “prime effect” of smells does not differ from our other physiological processes, which are always based on the stimulation of hormone production. In fact hormones are nothing else in structure that aromatic molecules, which are introduced into the blood circulation.
Therefore, wherein our hormones activate our own biological processes, our pheromones activate at distance the biological processes of others.

Smells of the human body

The most sought after pheromones  is the “primary pheromone“ that it supposed to render who wears it irresistible to potential partner. A pheromone found in the Rhesus monkey, “Copulin” has been researched in human vaginal secretions and has been experimented on males but without conclusive results.
The sweat glands are spread on the entire human body and produce three types of secretions, the apocrine glands are responsible for the production of smell. The development of the apocrine glands is a sexual characteristic and happens at the age of puberty, producing “adults” smells. The apocrine glands are present in quantity around to the nipples, on the genitals, under the armpits and on the hair skin.
They produce secretions under the effect of emotions, stress or sexual excitation. But many of body human smells are produced by bacterias and other microorganisms, who are working transforming little odorous secretions, like those apocrine or sebacee.
The characteristic smells of different parts of the body are the fruit of the interaction between these secretions and the microorganisms that live there.
The axillary secretions are the most studied by researchers because they are the exclusive patrimony of primates and of human beings, but also because those of males and of females are different and lastly because they are perceptible at a distance.
The ensemble of the sebacee glands, the eccrine and apocrine glands with the axillary hairs and the microorganisms living in the zone constitute “the axillary odorous organ”.
Axillary depilation reduces drastically the capacity of the organ to produce its typical smell.

In fact the apocrine secretions are little odorous when they are produced, because the fatty acids, the proteins and the steroids that constitute them are complex and heavy molecules, therefore with little volatility.
It is the incubation with the bacterias of the skin that “digest” them “cutting”  them that render them volatile, and odorous.
The main activity of the bacteria is to split acids from proteins to which they are bound at the moment of their production.
The axillary hairs multiply the living surface of the bacteria and multiply also the surface of evaporation of the smell.
The nature of the bacterial flora present on the armpits depends from the androgens levels of the persons, and this conditions also the smell produced from secretions.
The axillary secretions contain androstenol (also found in the urine) and androsterone (the scent of truffle), but also a great amount of aliphatic acids, other odorous steroids and compounds that are the “olfactory signature” of every person. There are also the smells from ingested foods and others caused by metabolic disorders (diseases).

The feminine secretions contain 50 times less androsterone than the male ones. Men and women produce for the greater part the same odorous molecules but their proportions change. For aliphatic acids,  for example, they are opposite.
The axillary flora as well is very different: for example men have a much higher proportion of coynebacterium.

It is indeed the extreme complexity of the system of odorous production that allows for each person his individual smell, and this is corresponded by an equally sophisticated possibility of perception by our olfactory organ.

But this is what renders traditional search in this field nearly impossible, because besides all the individual physical factors that condition the chemical-odorous production of humans (age, diet, health, cycle, sexual activity, etc), the psychological aspect, specific to the human being, affects in determining way this production, and for the investigators it is practically impossible to find subjects who are in the same psycho-physical conditions in order to be able to draw incontrovertible conclusions.

Research in the olfactory field therefore would have to assume the methods of the pure physics research rather than those of the traditional medical research, in order to be able to progress beyond the nearly total ignorance in which we are today in regard.



  1. What are pheromones?
  2. State of the research on pheromones
  3. Sexual pheromones
  4. Human pheromones