Breast's behest

Association for Chemoreception Sciences - Alison Motluk reports

The pheromones of breastfeeding mothers may be messing with your menstrual cycle.

Two years ago, Martha McClintock of the University of Chicago showed that women who live at close quarters really do tend to synchronise their menstrual cycles, backing the popular perception with hard evidence (New Scientist, 14 March 1998, p 6). Now her team has found that lactating mothers can also influence other women.

The researchers asked 26 breastfeeding women to wear absorbent pads in their armpits and inside their nursing bras. Then they asked 54 female volunteers to rub these pads under their noses four times a day for about two months. After the volunteers' first menstrual cycle, half the women got pads collected from the nursing mothers.

All the women had regular cycles before the experiment began. But the researchers found that among the women who sampled "eau de breast", short cycles became significantly shorter and long cycles became significantly longer. "Some kind of chemosignal from the breastfeeding environment is disrupting their cycles," says Natasha Spencer, a member of the team.

McClintock's team now wants to find out if the timing of pregnancies of groups of women can be synchronised by a chemical signal.

From New Scientist magazine, 06 May 2000.