The Chicago lab that discovered the first evidence of human pheromones in 1998 is making headlines again, this time with a study showing that breastfeeding women produce a compound that increases sexual motivation in other women exposed to it.

Martha McClintock, the David Lee Shillinglaw Distinguished Service Professor in Psychology and head of the lab that carried out the study, explained that the paper, titled “Social chemosignals from breastfeeding women increase sexual motivation,” shows that such an effect exists.

Chemosignals are hormonal chemical signals that the body uses to regulate its systems. Social chemosignals, or pheromones, are chemosignals that can affect other individuals. “Odors and flavor are also chemosignals,” McClintock said, making the point that we are constantly interacting with foreign chemosignals. This study is the first demonstration of a compound that affects sexual desire, McClintock said, adding that this was the third of three studies.

The researchers first developed a simple method of precisely determining when a woman is ovulating. This allowed them to show that sexual motivation changes over the cycle and peaks before ovulation, McClintock said. Only then did the lab measure the effect of the breastfeeding compounds on the timing of the menstrual cycle and on sexual motivation, finding that there is a measurable effect.

Suma Jacob—the primary author of the study on the timing of the menstrual cycle and a clinical and research fellow at the U of C Hospitals—explained that the menstrual cycle study was a piece of the larger study, along with the sexual motivation study. Once the groundwork in measuring the exact timing of ovulation had been laid, the second or third studies were possible.

According to the published paper, the sexual motivation study was carried out by exposing 47 Chicago-area women to sweat and breast milk compounds collected from 26 lactating Philadelphia-area women. Julie Mennella at the Monell Chemical Senses Center in Philadelphia put together the collection of the compounds used in the study. As the women in the study were exposed daily to the breastfeeding compounds, they also had to undergo psychological evaluations and fill out a daily journal recording the level of sexual desire they experienced and the number of sexual fantasies they had that day.

An interesting finding of the study, McClintock said, was that “the way these compounds were experienced had to do with whether the women had a regular sexual partner or not.” She said that women with regular partners showed “the effect on the scale of desire while women without a partner experienced the effect on the scale of fantasy.”

Maren Hulden, a third-year in the College, expressed hope for the possibilities this type of research opens up, saying, “I think that more often than not we will be able to use these [findings] to our advantage.”

McClintock held a similar view, saying that she saw potential applications for the effect identified in the sexual motivation study, perhaps to help treat women suffering from chronically low sexual desire.

Sam Jacobson, a fourth-year in the College, took a dimmer view, saying that this research puts people “into a very narrow and reductionist framework.” Jacobson continued jokingly, “Men are more complex and mysterious things.”

Suma Jacob recognized the tendency to view her research in this manner. “People become very concerned when anything can affect behavior that you’re not in conscious control of,” she said, adding, “this is a piece of information that our brain processes along with all the other senses. From that it can have some influence on psychological systems.”

Additionally, a study of Jacob’s involving previously known chemosignals showed that pheromones affect men as well as women. “Men and women both had psychological effects, but the effects were different.” She cautioned that there is no reason to believe that women are affected by chemosignals to a greater extent than men. However, she continued, the effects of chemosignals are “harder to test in men.”

“I think [chemosignals] is an area that needs to be studied more,” Jacob said. “I’d want to see this done again, fine tuning it.” McClintock agreed, saying, “This is the kind of research that opens a door. This shows there is a phenomenon to be studied.”