In many species they are detected by a specialized organ inside the nose or mouth called the vomeronasal organ, or VNO. There was ample evidence that human pheromones exist; babies show a clear preference for pieces of clothing that have been worn by their own mothers, for example, and research suggests that men and women choose their mates in part by sniffing out partners with compatible immune systems.



The research settles a 40-year debate about whether humans produce and can respond to "pheromones," molecules that are usually airborne and odorless and which, in other species, influence such physiological processes and behaviors as mate choice, the recognition of one's own family members, and the ability to "smell" the difference between friend and foe.

The studies made by a lady, McClintock, proved the existence of Pheromones in human beings. Specially, her researches showed that the pheromones released by women's under arms can alter the timings of women's reproductive cycles. This explains why women who live together often develop synchronous menstrual periods and could spur development of natural fertility drugs or contraceptives.

"The evidence has now become quite strong that humans produce and detect pheromones," agreed Edward W. Johnson of Idaho State University in Pocatello.

The discovery was especially gratifying to Martha K. McClintock, the University of Chicago researcher who, with colleague Kathleen Stern, describes the work in one of the issues of the journal Nature. As an undergraduate almost 30 years ago, McClintock observed that many women in her dormitory menstruated in synchrony. For decades McClintock immersed herself in the task of identifying the timing mechanism. She and others suspected pheromones, but proof was hard to come by.

Sweat is a common source of pheromones in mammals. To find out if human pheromones exist and can affect menstrual timing, McClintock and Stern asked nine women to wear gauze pads under their armpits all day. The pads, changed daily, were cut into pieces and frozen, and a daily tally was kept of each woman's menstrual phase.

Then, every day for four months, the researchers rubbed thawed gauze pads which contain sweat pheromones, above the upper lips of 20 volunteer women who had agreed to have any of 30 different "natural essences" rubbed under their noses. For two months, 10 women sniffed sweat from women in the early phase of their menstrual cycle, while the other 10 sniffed sweat from women in a later phase of their cycle. Then the groups switched and spent two months getting the opposite scent.

The women smelled nothing, but the results were striking: Those exposed to "early phase" sweat saw their own cycles shortened by an average of 1.7 days per month, and as much as 14 days a month. Those who sniffed "later phase" sweat saw their cycles lengthened by an average of 1.4 days a month, and up to 12 days a month. This is now called as MaClintock's effect of Pheromones.

Computer models indicated there must be two substances in the sweat one that lengthens cycles and one that shortens them and that together they can quickly lead to groups of women having synchronous periods.

If pheromones have a big effect on human physiology, people may want to rethink their heavy use of soaps and perfumes: It may be, Buck speculated, that the constant washing away or covering up of these sweaty social signals account for some of the loneliness or depression in modern society.