Olfactory influences on the human menstrual cycle.

Two groups of women were compared for the timing of the onset of their menstrual cycles. One group was rubbed on the upper lip (directly beneath the nose) with a mixture of alcohol and underarm perspiration collected from a single female donor. The other group was rubbed with plain alcohol. The group which received the perspiration showed a significant shift in the timing of their menstrual cycles which conformed closely with the donor's monthly cycle. This is a preliminary study which supports the hypothesis that the time of menstrual onset may be modified by olfactory cues.