Definition: A chemical substance that is produced by an animal and serves especially as a stimulus to other individuals of the same species for one or more behavioral responses -- called also ectohormone
-1997 by Merriam-Webster, Incorporated
To the scientist, pheromones act in a very different way from normal smells. Some years ago, researchers discovered the existence of a small organ in the nose of many animals (known as the VNO), which has a direct affect on social behavior. What makes this discovery important is that the VNO/pheromone effect is not dependent on any conditioning through experience. It is direct.
Here is an example. If a man has sex with a particular woman regularly over a long period of time, and on every occasion she wears a particular cologne, gradually this scent will acquire the power of stimulating (attracting) the man all on its own. It is then very likely that any woman wearing this cologne will be perceived as attractive to the man. This is a pheromone-like reaction but in the strict definition of the word is NOT a pheromone reaction! It is acquired conditioning, similar to that of Pavlov's salivating dogs.
Pheromones do not depend on such associations with prior experience to do their work. They utilize a special organ (the VNO), which is separate from the normal smelling process. There is still much arguing about the presence of this VNO in humans, but it is well accepted that pigs and cows in the vicinity of the sex pheromones of their species will be rendered "in the mood" even if they have no sexual experience, as long as the VNO is intact. If this VNO is damaged, sex will only take place if the animal has prior sexual experience. In this case the pheromones are still acting as a sexual attractant, but only because they remind the target of previous sexual encounters.
Here, I believe, is the crux of the great debate among scientists as to whether pheromones really work on humans or not, though I have yet to see this clearly stated anywhere. The VNO organ does physically exist in humans just as in other animals, but many scientists believe that it has been rendered ineffective by ages of disuse. Even human pheromones greatest supporters admit that humans are not as greatly led around by their VNO as pigs and cows, but on the other hand 100% uselessness of the organ is also hard to believe.
Forget about the VNO and pheromones for a moment, and take a look at the difference between dogs and humans in the normal everyday ability to detect smells. Both species have the same physical smelling apparatus, but the dog wins a sniffing competition easily. Probably prehistoric man could smell a dinosaur coming a mile away, but nowadays we don't depend on our sense of smell for survival as much as vision and other faculties, so it has gotten a little weak from disuse. BUT, this does not mean that our sense of smell is 100% useless, and I suspect that the VNO/pheromone function is also not 100% out of order, just weaker than in other animals.
A number of pheromones and pheromone-like substances have been isolated in humans, and have been shown in scientific studies to have an affect on a variety of human behaviors and hormonal processes. Whether these effects are 100% "true" pheromone reactions or not is an interesting point and worthy of further investigation, but is a moot point to the perfume industry. The effects of pheromones may be modulated by the sexual experience of the target and/or by the extent to which the target's VNO is still functional, but the fact is that a number of controlled human studies have shown that pheromones both natural and synthetic/supplemental do affect our social behavior, and a growing mountain of raving pheromone product testimonials also support these findings. Furthermore, I have yet to come across even one pheromone study that has failed to show some significant effects from pheromones, and until that happens there is little alternative but to assume that pheromones work.
A number of human pheromones have been isolated and studied. Not all of these are of interest to those searching for a mate. In fact some pheromones have been shown to decrease testosterone levels and thereby the mating instinct! In all the studies I have come across, I have found 3 human pheromones that have been found effective for attracting members of the opposite sex: androstenol, androstenone, and copulins.
Androstenol and androstenone are pheromones which are created on the skin of both sexes when chemicals in human sweat interact with common bacteria. Both have been found to influence human attraction.
The strictly female substance, copulins, which is found in human vaginal secretions, has been shown to both elevate male testosterone levels (directly linked to increased sex drive), and positively affect perceptions of female attractiveness in targeted males.