A series of short-chain fatty acids (copulins), produced by bacterial action from components of vaginal secretions, are involved in the olfactory communication of the female's sexual attractiveness to the male. In intact females, the content of acids in vaginal lavages decreases at midcycle when the female's attractiveness is highest. To test if this apparently anomalous decrease was due to an increase in the rate at which secretions were externalized, 422 wipes of the sexual skin area were collected during 19 menstrual cycles and analyzed for short-chain fatty acids. Despite considerable day-to-day variations there was a trend for the acid content of the wipes to increase at mid-cycle, a result that was consistent with there being an increased flow of secretions to the outside at this time. Other factors besides the rate of externalization may also regulate the strength of the olfactory signal, and the present results are consonant with a role for these acids in signaling the fertile period to the male.
Sex attractantpheromonevaginal secretionprimatemenstrual cycle