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Oct. 8, 2004 -- Breastfeeding mothers and their babies produce a chemical that can boost other women's sexual desire, new research shows.

It's a natural phenomenon found in animals -- the production of chemicals called pheromones that regulate all sorts of reproductive behaviors and processes in other females, and possibly sexual desire, writes researcher Natasha A. Spencer, PhD, with The Institute for Mind and Biology at The University of Chicago.

The presence of women who are breastfeeding may be a signal to fertile women that they, too, support the demands of pregnancy and lactation, writes the author.

In a previous study, Spencer and colleagues reported that fertile women were dramatically affected -- specifically a women's period and the timing of ovulation was changed when exposed to these pheromones, she says.

But what about the women's sexual desire and fantasies -- the true measures of their motivation for sex? Will her partner benefit from her lust? If she has no partner, will she conjure up one through fantasy? That's what Spencer's study checked out.

Pheromones Trigger Sex Drive, Fantasies

In their study, Spencer and her research group collected the natural "breastfeeding compounds" from 26 mothers who wore pads in their nursing bras, where the saliva from their infants plus their own perspiration and milk was collected. They also wore underarm pads to collect perspiration.

The breastfeeding pads were then cut into pieces and frozen.

Then, 90 women between ages 18 and 35 -- none of whom had given birth -- were assigned to either the breastfeeding pads or a placebo pads group. They were asked to swipe the pads under their noses in the morning, at night, and when they wiped their upper lips, showered, or exercised during the day.

The women also tracked their lust; those with a sexual partner rated their sexual desire; they also recorded their sexual activity. Those without sexual partner recorded their moods and whether they had any sexual fantasies.

After two months of smelling pheromones from the breastfeeding mothers, women with regular partners showed a 24% increase in sexual desire, and women without partners had a 17% increase in sexual fantasies, she reports.

Among women who got placebo pads, those with partners had a slight decrease in sexual desire. Women without partners had a 28% decrease in fantasies.

"The effect became striking during the last half of the menstrual cycle after ovulation, when sexual [desire] normally declines," says co-researcher Martha McClintock, PhD, a Distinguished Service Professor in Psychology at The University of Chicago, in a news release.

The phenomenon likely evolved in early primitive societies, when women produced children during times when food was plentiful. The pheromones would have been a way of encouraging other women to reproduce during this plentiful time.

In 1998, McClintock and her colleagues produced the first evidence of human pheromones. However, more research is needed to determine if the breastfeeding chemicals are indeed pheromones that trigger sexual desire, she adds.

Their paper on sexual desire appears in this month's issue of the journal Hormones and Behavior.

SOURCES: Press release, The University of Chicago. Spencer, N. Hormones and Behavior; vol 46: pp 362-379.

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