McClintock points to her 1998 Nature paper, which found that women exposed to cotton pads soaked with underarm secretions collected from donors undergoing the first and second (follicular and luteal) phases of their cycles resulted in significantly altered menstrual cycle lengths in the test women. The results, however, rested on a knife-edge of statistical significance, Schank says, and could have been due to chance.
But a team of Japanese researchers at Yokohama City University, led by Kazuyuki Shinohara, also found in a series of papers that donor women undergoing these two phases of the menstrual cycle release compounds that when inhaled by other women can significantly impact the frequency in the latter of pulses of luteinizing hormone (LH), which helps control the timing of ovulation and cycle length.
Similarly, a 2004 study from McClintock's group found that odors from breast-feeding women alter the timing of the cycles and LH surges in childless women.
McClintock is still actively researching the area. The most important questions, she says, are exploring the underlying mechanisms behind variation in the social effects on ovulation: Why do some women not respond? Why are some phases of the menstrual cycle more sensitive to external stimuli?
"I completely agree with Jeff [Schank]. There are no perfectly lock-phased cycles that are sustained over 20 cycles; that is very rare. But given what I know about the causes of menstrual synchrony means I expect it to be rare," she says. "So the fact that it is rare doesn't mean that it doesn't exist."
But until the relevant pheromones and their biochemical receptor pathways are better described, the current bulk of evidence suggests that popular notions of menstrual synchrony are more college town myth than dorm room reality.