Men smelling women: null effects of exposure to ovulatory sweat on men's testosterone.

Males of many species, humans included, exhibit rapid testosterone increases after exposure to conspecific females. Female chemical stimuli are sufficient to trigger these responses in many nonhuman species, which raises the possibility of similar effects in humans. Recently, Miller and Maner (2010) reported that smelling T-shirts worn by women near ovulation can trigger testosterone responses in men; however, men were aware that they were smelling women's scents, and thus mental imagery associated with that knowledge may have contributed to the hormone responses. Here, we collected axillary sweat samples from women on days near ovulation. In a crossover design, men who were not explicitly aware of the specific stimuli smelled the sweat samples in one session and water samples in a second session. There were no differences in testosterone responses across the experimental conditions. Our null findings suggest that the relevant chemical signal is not found in axillary sweat, and/or that knowledge of the stimulus source is necessary for hormone responses. These results thus suggest boundary conditions for the effects reported in Miller and Maner (2010), and recommend further research to define the precise circumstances under which men's testosterone may respond to chemosensory cues from women.