322 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS men. This was also true for a 'neutral' odour like m-xylene but here again the difference was much less marked. According to some authors the incidence of a specific anosmia, i.e. total incapacity to perceive a specific odour, is much more widely spread among adult men than among adult women. Le Magnen (2) reported that about 50•o of the adult males show an anosmia for cyclopentadecanolide. Griffiths and Patterson (8) found that 7.6•o of the women in their experiment were unable to detect the odour of androstenone, in contrast to 44'3•o of the men. However, Whissell- Buechy and Arnoore (9) found no sex difference in the incidence of pentadeca- lactone anosmia. They found significant differences in the frequencies of specific anosmias between two human races: the musk anosmia occurred in about 7•o of the Caucasians but in none of the Negroes, whereas the anosmia for isovaleric acid was prevalent (about 95/0) among Negroes and uncommon (about 1•o) in Caucasians. The inability to smell pentadecalactone seems to be inherited as a simple recessive autosomal character. Comfort (10) pointed out that these results raise several points of biological interest, as both isovaleric acid and musks are candidates for consideration as functional pheromones, the former at any rate in monkeys. Koelega and K/Sster (7) were not able to show occurrence of a specific anosmia for musk or androstenone in a systematic way. Sometimes a person who could not smell the highest concentration presented to him (or her) in a particular session of the experiment, did quite well on other occasions. Much seems to depend on the method of stimulus presentation used and on instructions. The general hypothesis forwarded by Broverman et al (5) cannot explain why the differences found in the adult groups are much more pronounced for the biologically meaningful odours than for the other odours and why a sex difference for amyl acetate should be found at an early age when the sex hormones are not yet active. Differences in motivation may have contributed to this difference among young subjects, although Koelega (7) tried to hold motivation constant by the prospect of rewards for the best smellers. The specific hypothesis of Le Magnen (2) is supported to some extent by these results since the sensitivity for the biologically significant odours seems to develop well only under the influence of the female sex hormones adult women are clearly more sensitive than men for these odours. However, Le Magnen's (2) hypothesis also suggests a greater sensitivity in men than in women for biologically non-significant odours like amyl acetate and m- xylene. The results of the experiments do not support this. In fact, women do slightly better on these odours too. Motivational differences and differential smoking habits might contribute to this result.

SEX DIFFERENCES IN ODOUR PERCEPTION 323 DIFFERENCES IN VARIABILITY OF THE SENSITIVITY Although women are in general perhaps more sensitive to odours than men, they also show larger variations in their sensitivity. These variations seem to be linked with variations in sex hormone production. Le Magnen (2) was the first to demonstrate that for exaltolide there existed a relationship between the olfactory sensitivity in women and the course of their ovulatory cycle. During menstruation the sensitivity is at its lowest. Shortly after- wards the sensitivity goes up to a maximum situated in time around or just before ovulation. Then there is a rather sharp fall in sensitivity to a level just above the one found at menstruation. This level is maintained until the onset of menstruation. Vierling and Rock (11) confirmed Le Magnen's (2) finding with exaltolide, however, they found two increases in sensitivity: one just before the theoretical ovulation (17 days before menstruation) and one during the luteal phase (8 days before menstruation). Le Magnen (2) had also found such a second peak in acuity in a woman with a long cycle. In line with this specific hypothesis Le Magnen (2) supposed that his result would be specific for exaltolide and other 'biologically significant' odours. He used several other substances, but the curves obtained for these substances show very little variation over the same period. Meixner (12) also confirmed Le Magnen's (2) result with exaltolide but found that the acuity for pyridine, a urinoid odour according to Le Magnen (2), did not parallel the fluctuations found for exaltolide but was probably related to the phases of the menstrual cycle, whereas sensitivity to two neutral odours, although varying together, was not related to the menstrual cycle. The results indicated specific rather than generalized changes in olfactory sensitivity during the female sexual cycle. Kahn (13) obtained inconsistent data for three neutral odours, but the number of measurements in this experiment was small. Schneider and Wolf (14), using a neutral odour (citral) as a stimulus found a decrease in the sensitivity during menstruation, but they did not find the marked increase of the sensitivity around ovulation. Since the decrease in sensitivity during menstruation may well have been an artefact resulting from lack of motiv- ation during that period, Le Magnen's (2) claim of the specificity of the effect was not seriously challenged by these results. However, in a number of experiments, K/Sster (15, 16) was able to show that similar variations of the olfactory sensitivity with the ovulatory cycle could be found for another 'neutral' odour (m-xylene), although the variations were definitely less pronounced than in Le Magnen's (2) study. He also found that the variations observed are dependent upon ovulatory cycle duration. Women with short (28 days or somewhat less) cycles behave exactly in the way described by Le Magnen (2), but women with long cycles behave in the opposite way. This has been confirmed in two separate experiments