The first scientific evidence for the existence of human pheromones has come from a study of women whose menstrual cycles were manipulated using secretions from under their arms.
Psychologists Kathleen Stark and Martha McClintock, of the University of Chicago, Illinois, asked nine women to wear cotton-wool pads under their arms for eight hours.
They were treated with alcohol, frozen and then the secretions from them applied to the upper lips of 20 other women who were asked not to wash their faces for at least six hours. The recipient women repeated the process daily through two complete menstrual cycles.
The researchers found that when the secretions were taken from the nine donors in the follicular phase of the menstrual cycle, two to four days before ovulation, they shortened the menstrual cycle in the recipient women.
But when the secretions were taken from the donor women in the ovulatory phase, the day of ovulation and the two subsequent days, they lengthened the menstrual cycle in the recipient women.
The finding, reported in Nature, helps explain why women living together can develop synchronised menstrual cycles. The two types of pheromone appear to regulate follicular development (the maturation of the follicle that produces the egg) and ovulation but not other stages of the menstrual cycle.
The study shows humans have the potential to communicate pheromonally and raises the question whether there are other human pheromones that might influence other aspects of behaviour.
None of the recipient women could detect the pheromones, reporting only a smell of alcohol, used to extract them from the cotton-wool pads. In all, two-thirds responded by lengthening the menstrual cycle by an average 1.7 days or shortening it by an average 1.4 days.
The researchers say that the pheromones may have other effects on women depending on their social conditions and the point in their reproductive life. Research in animals has shown that they influence mating preference, dominance relationships, and recognition of individual members of their social group.Reuse content