Gender-specific olfactory sensitization: hormonal and cognitive influences.

In one reported instance of induced olfactory sensitivity, men and women who were initially unable to smell androstenone (5-α-androst-16-en-3-one) developed that ability after repeated exposures (Wysocki et al., 1989). This phenomenon has been believed to occur only for odorants to which participants have specific anosmia and possibly specific to the particular stimulus used in that experiment. Here, we demonstrate that induced olfactory sensitivity is both a more general and more restricted effect, with only women of reproductive age showing marked sensitization to multiple odorants after repeated threshold testing. These findings may offer an explanation for anecdotal claims of females' olfactory acuity. Although gender differences have been observed within several different olfactory processes, these tend to be tasks that require higher cognitive processing such as memory for odors, odor identification and hedonic ratings (Cain, 1982; Doty et al., 1985; Gilbert et al., 1997). Studies looking at olfactory sensitivity have failed to show such gender differences. However, such studies have relied on single session evaluations, whereas the present studies demonstrate that repeated exposure is an important factor in inducing sensitivity (cf. Cain and Schmidt, 2002). Although males and females may begin a study with comparably similar olfactory detection thresholds, under some conditions, females of reproductive age will sensitize to odor stimuli by up to 11 orders of magnitude, while their male counterparts will not. The phenomenon presented here was first encountered while repeatedly measuring taste and olfactory thresholds. Males and females between the ages of 20 and 32 were exposed repeatedly to benzaldehyde via a modified staircase method with a five-reversal criterion (Wetherill and Levitt, 1965). Oral saccharin thresholds were taken separately, each for a total of 30 sessions. Females' thresholds increased significantly, while males' did not (Figure 1). A two-way ANOVA with gender as a between-group factor showed that benz-aldehyde thresholds decreased among females but not among males [F(29,116) = 3.84; P = 0.007]. This effect was seen among women in as few as six sessions [F(1,5) = 4.20; P = 0.02]. Oral saccharin thresholds remained unchanged over 30 sessions among both males and females, indicating that this phenomenon is specific to the olfactory modality. An additional study was completed with control odorants to evaluate whether participants' sensitization to benzaldehyde would generalize to other odorants in the absence of extended exposures to those odorants. Six trained participants from the previous experiment as well as six naïve participants took part in the …