Breast Feeding & Social Chemosignals

A fascinating study conducted by the University of Chicago and the Monell Chemical Senses Center has found that women’s sex drives surge when they are exposed to the chemosignals of other women who are breastfeeding, likely because it signals to them on an unconscious level that environmental and other circumstances are optimal for having a baby.

“This is the first report in humans of a natural social chemosignal that increases sexual motivation,” says Martha McClintock, lead researcher in a team at the University’s Institute for Mind and Biology which, in 1998, produced the first evidence of human pheromones. Chemosignals are substances that, while not necessarily perceived as odors, enter through the nose and have an impact on mood and menstrual cycles.

In Philadelphia, Julie Mennella of the Monell Center recruited 26 breastfeeding women who were asked to eat a bland diet and wear pads in their nursing bras, where their own perspiration and milk was collected along with saliva from their infants. Meanwhile, in Chicago, McClintock’s team gathered about 90 women between ages 18 and 35 who had not borne a child and divided them into two groups, one exposed to the actual breastfeeding pads and the other exposed to pads soaked with potassium phosphate, a substance that mimics the concentration of sweat and breast milk. The participants were asked to swipe the pads under their noses throughout the day at any time when they might have wiped their upper lips, showered, or exercised. Women with sexual partners were asked to complete a daily survey rating the degree to which they felt desire for sexual intimacy during each day, while women without partners were asked to report “any fantasies/daydreams today of a sexual or romantic nature.” All subjects were kept in the dark as to the nature of the study and the source of the compounds they were sniffing.

After being exposed to the breastfeeding compounds for two months, women with regular partners experienced a 24% increase in sexual desire, while women without partners reported a 17% increase in sexual fantasies. The control group showed an insignificant decrease in sexual desire for women with partners, and a 28% decrease for those without. “The effect became striking during the last half of the menstrual cycle after ovulation when sexual motivation normally declines,” says McClintock.