The term pheromone is derived from the Greek "pherein", i.e., to bring or to transfer, and "hormon", i.e., to excite. Pheromones are chemical substances released by one member of a species as communication with another member. They are behaviour-modifying substances transmitted between both insects and mammals by smell or by contact. Pheromones are substances that are secreted externally, and when received by another individual, they elicit a behavioural or developmental response in the latter. This response is usually of a sexual or of a reproductive nature, but may also include other social responses as well.
Pheromones were first identified in insects, but more recent studies show that pheromones influence the lives of a wide range of organisms, from microbes to man. Pheromones may be present in many different sites, including the skin, saliva, urine, vaginal discharge and faeces. In humans, it is believed that pheromones bind to chemosensory receptor cells of the vomeronasal organ in the nose and induce a variety of social and reproductive behaviors. The vomeronasal organ was earlier thought to be a vestigial structure in humans, but it is now believed to be a functional organ. Stimulation of the vomeronasal organ can induce sexual behaviour and changes the hormonal status of males and females. Male pheromones (androstenol/androstenone) from male sweat can have an impact on female menstrual cycles and ovulation, while female pheromones (copulins) present in vaginal secretions can influence male perception of females and may induce hormonal changes in males.
Studies involving the use of pheromones in men have shown that human male pheromones affect the sexual attractiveness of men to women, and pheromone users have increased sexual activity. Likewise, pheromones can also increase the sexual attractiveness of women to men. Stimulation of the female vomeronasal organ with androstadienone can result in changes in autonomic activity, with a significant reduction of nervousness, tension and other negative feeling states being reported. In women, pheromones may play a role in the modulation of the timing of ovulation by changing the frequency of pulsatile LH secretion. Odourless compounds from the axillae of women in the late follicular phase of their menstrual cycles can accelerate the preovulatory surge of luteinizing hormone (LH) of recipient women and shorten their menstrual cycles. Axillary compounds collected later in the menstrual cycle (at ovulation) have an opposite effect on the recipients, i.e., a delayed LH surge and longer menstrual cycles. The effects of women's pheromones on each other can be seen in women living together in dormitories, who often have synchronized menstrual cycles. In studies involving menopausal women, a topically applied synthetic pheromone increased sexual attractiveness. If partners are available, sexual attractiveness can increase affectionate intimate behaviour, which, in turn, can increase well-being and quality of life.
Apparently, pheromones play important roles in both males and females. An interesting use of these agents could involve their application on the body to facilitate attraction to the opposite sex. Undoubtedly, there exists a huge scope for such usage, but more studies are required to confirm the exact role of pheromones for this indication. Nevertheless, the concept of pheromones is obviously an appealing one, because several pheromone products are already commercially available to facilitate sexual attraction and/or to improve a current relationship. Pheromones have been incorporated into perfumes and cologne, adding new dimensions to a fragrance market that is already worth billions of dollars.
Apart from their use in humans, pheromones can be employed in agricultural pest control to disrupt mating and reduce the insect population. Thus as a category, pheromones can play important new roles in our lives. Surely we will be hearing a lot more about pheromones in the future.