8 October 2004
Chemosignal Unlocks Sexual Desire In Women
by Kate Melville
Breastfeeding women and their infants produce a pheromone-like chemical that increases sexual desire among other women, according to researchers at the University of Chicago. The research is reported in the latest issue of the journal Hormones and Behavior.
"This is the first report in humans of a natural social chemosignal that increases sexual motivation," said Martha McClintock, the lead researcher. Chemosignals are substances that while not necessarily perceived as odors, nonetheless have an impact on mood and menstrual cycles when absorbed through the nose.
McClintock and her team found that after being exposed to the breastfeeding compounds for two months, women with regular partners experienced a 24 percent increase in sexual desire. Women without partners experienced a 17 percent increase in sexual fantasies after exposure.
The research involved recruiting breastfeeding women, who were asked to eat a bland diet to avoid transmitting odors such as curry through the breast milk. The breastfeeding women wore pads in their nursing bras, where the saliva from their infants in addition to their own perspiration and milk was collected. They also wore pads secured by underarm shields to collect perspiration. The pads were then collected, cut into pieces and frozen. McClintock says that this procedure is effective in collecting chemosignals.
The researchers also recruited women between the ages of 18 and 35 who had not born a child. The women were divided into two groups, one group exposed to the pads with breast feeding substances, and the other group exposed to pads with potassium phosphate, a substance that mimics the concentration of the sweat and breast milk.
"Because preconceived ideas about pheromones could potentially influence their responses, study participants were blind to the hypotheses and the source of the compounds," co-researcher Natasha Spencer said. "The study was presented to the subjects as an examination of odor perception during the menstrual cycle."
Participants were given a set of pads on a regular basis and asked to swipe them under their noses in the morning and at night and any other time of the day in which they may have wiped their upper lips, showered or exercised.
The women were asked to complete a daily survey with a scale indicating "the degree you felt desire today for sexual intimacy." They also recorded their sexual activity. Women without partners were also asked about their moods and reported whether they experienced "any fantasies or daydreams of a sexual or romantic nature." Among women exposed to the breastfeeding substance, "The effect became striking during the last half of the menstrual cycle after ovulation when sexual motivation normally declines," McClintock said.
The researchers say that further study is needed to determine if the chemosignals are pheromones. In order to be pheromones, researchers much show that the substances operate "in the context of normal daily interactions with breastfeeding women and their infants. Ideally, such a study would also demonstrate how these effects would have increased the evolutionary fitness of individuals who used this system of social communication during human evolution," McClintock explained. Other studies suggest that women living in early societies produced children when food resources were plentiful. The chemosignal would have been a way of encouraging other women to reproduce during those plentiful times.