Researchers show existence of human pheromones

By William Harms
News Office

Martha McClintock, Professor in Psychology, has provided the first conclusive scientific evidence for human pheromones, compounds undetectable as odors but which have a major impact on the timing of ovulation. Her findings were published in the March 12 issue of Nature. "These data demonstrate that humans have the potential to communicate pheromonally, either by using an unidentified part of the main olfactory system, or perhaps with a sixth sense, with its own unique pathway," McClintock writes in the paper, which she co-authored with Kathleen Stern (Ph.D.'92), a researcher in private industry. Because the pheromones regulate the length of the menstrual cycle and can help influence the release of eggs, the compounds have the potential of providing a new, more natural way of preventing pregnancy, as well as treating infertility.

The work of McClintock and Stern establishes the presence of two pheromones. One, produced prior to ovulation, shortens the ovarian cycle, and the second, produced just at ovulation, lengthens the cycle.

McClintock, whose work builds on early studies showing that women living together develop synchronized menstrual cycles, conducted the study on 29 women between the ages of 20 and 35 with a history of regular and spontaneous ovulation.

From nine of the women, the researchers gathered samples of compounds by placing pads under their armpits. The samples were taken at distinct phases of the menstrual cycle. After the pads were treated with alcohol and frozen in glass vials, they then were swiped under the noses of the 20 other women in the group.

The researchers found that "compounds donated by women in the late follicular phase (the early portion) of their menstrual cycles accelerated the preovulatory surge of luteninizing hormone (LH) of recipient women, and shortened their menstrual cycles."

They also found that "compounds from the same donors, but collected later (at the time of ovulation) had an opposite effect, delaying the LH surge of recipients and lengthening their menstrual cycles."

The researchers found that 68 percent of the women responded to the follicular pheromones while 68 percent responded to the ovulatory pheromones. The other women were unaffected by the compounds.

"In addition, the range of response magnitude was considerably more than variation in cycle-length typical for this age group -- cycles were shortened from one to 14 days and lengthened from one to 12 days," according to the researchers.

The research follows other studies done in McClintock's laboratory on rats and the effect of pheromones on their behavior. In rats, as in other animals, pheromones play a major role in regulating behavior.

"For example, pheromones affect with whom male and female hamsters mate, dominance relationships among male elephants, when rat mothers wean their pups and how they teach pups to distinguish edible food from poisons, how hamsters recognize individual members of their social group, and the level of stress experienced by a mouse in a new environment, which is based on the emotional state of the previous occupant," McClintock said.

McClintock cautions that humans are probably not as strongly influenced by pheromones as other animals, particularly in the area of mating. Many other factors influence the choices people make in romance, she said.

Her current research does point, however, to a need to expand scientific exploration on the existence of pheromones.

"Well-controlled studies of humans are now needed to determine whether there are other types of pheromones, and if they have effects as far-reaching in humans as they do in other species," she said.