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Do men and women differ in their capacity to detct odors?

Shiva Vafai

According to studies performed before the turn of the century (Bailey & Nichols, 1884; Bailey & Powell, 1885), it was believed that men possessed greater sensitivity to odors in threshold studies than did women. Albeit, these studies, both from the same laboratory, did not report the details of their experiments, except that twenty subjects of each gender participated. Neither the ages of the participants, the testing procedure, nor the number of replicates performed, if any, were reported. Since the publication of these studies, there has been no conclusive evidence in support of the findings of these experiments. In fact, the overwhelming evidence has provided support for the opposite contention, that women possess greater sensitivity to odorants.

Koelega and Koster (1974) conducted experiments involving a modified method of constant stimuli of several hundred subjects, reporting lower female thresholds for the nine substances tested. Experimentally, threshold measures and sensitivity are considered to directly correspond. Koelega and Koster also found that prepubescent girls out performed prepubescent boys on a number of odor detection tasks. The substances involved in the experiment included amyl acetate, androstenone derivatives, exaltolide, xylene, and pyridine.

The experiments of Toulous and Vaschide (1899), Le Magnen (1952), and Schneider and Wolf (1955) also support the notion that females possess greater sensitivity to odors in threshold studies.

In addition to the well-documented superior female performance noted in these and more recent odor-identification studies (Doty, 1981), other studies reveal that the sex difference may be observed in all decades of life. This is in direct objection to the widely-accepted belief that sex differences in olfactory perception are due to differences in gonadal hormone levels (Doty & Snyder, 1981).

It is not surprising that sex differences with regard to smell sensibility exist, especially in light of studies which reflect similar differences in performance between the sexes in vision, hearing, tactile, and kinesthetic experiments (McGuinness, 1976).

The most extensive study heretofore conducted on odor perception on a large scale is the classic Smell Survey sponsored by the National Geographic in its September 1986 issue. The Smell Survey, comprised of a questionnaire and a set of six microencapsulated odorants, was distributed worldwide to 10.7 million members of the National Geographic Society. Of the 1.5 million surveys which were returned, the results of nearly 1.2 million United States respondents between the ages of 10 and 90 provide the basis for the conclusions herein discussed. Respondents characterized the odors, namely, androstenone (sweat), isomyl acetate (banana), galaxolide (musk), eugenol (cloves), mercaptans (natural gas warning agent), and a synthetic rose scent, according to a set of category descriptors. The huge sample size and broad range of the survey provides data which can be used to investigate further possible correlations with specific demographics of the sample population, including gender (Gilbert & Wysocki, 1987).

Certain aspects of the sample surveyed are to be noted to prevent misapplication of the results bias (Wysocki & Gilbert, 1989). The data are not considered to be representative of the United States. More women than men participated in the survey, which may indicated a positive female response Additionally, it may be worthwhile to mention that the vast majority (95%) of the participants identified themselves as white. The average age of the respondent was 43.3 years. Though the gender differences were small, they were consistently evident in the survey results.

Self-Rating:

Throughout the nine-decade life span distribution, women thought they had better olfaction than men, and generally, they did. The smell-ability self-ratings declined for both sexes, though women's self-ratings increased until the fifth decade, at which point the self-ratings decreased, with accelerated decline in the eight decade; Men's smell-ability self-ratings declined more conistently across the age distribution, though the range of self-ratings for both sexes represented 11% of the entire rating scale.

Insert graphs WYC and GIB p 16

Perception/Intensity:

Women of all ages more frequently perceived androstenone and galaxolide. Both men and women generally detected the other four odors with equal degree of perception until the fifth decade, after which time women more frequently perceived the odors. Across the lifespan, women correctly identified all six odors more frequently than did men.

Insert graphs WYC and GIB p 17 and 19 and 20

Pleasantness:

In rating the quality of the odors, the responses of the participants divided according to sex for each odor, though the relationship between the sexes was inconsistent. Men found the androstenone, isomyl acetate, and mercaptans to be more pleasant, and women found eugenol and rose to be more pleasant. Women generally found Galaxolide to be more pleasant than did men, with slightly declining ratings after the fourth decade; men generally demonstrated a similar pleasantness rating distribution, except with a sharp increase in the ninth decade of life.

Insert graphs WYC and GIB p 24 A microscale experiment was conducted in our classroom using the National Geographic Smell Survey. The raw data may be accessed from the “class.xls” file. Unfortunately, due to the small sample size and the disproportionate male - female ratio, we found it difficult to draw any conclusions as a whole from the data collected. However, a mini-questionnaire (modelled after the Smell Survey) and a spreadsheet may be found in the aforementioned “class.xls” file for use in future surveys of this nature.

In conclusion, it is suggested by the literature available that there exists slightly superior female performance in odor-identification studies, a trend observed consistently in all ages of life. However, due to the difficulty in testing and quantifying olfactory acuity, the experimental data from which conclusions have been made are not as scientific in their method or in their accuracy as would be ideal; neither are the data as dependable as the information available from sex-differences studies in regard to the other senses. It is hoped that future investigation in the field of olfaction may lead to more precise tools and methods with which to test the hypothesis that women possess greater olfactory prowess.

References

Bailey, E.H.S. and Nichols, E.L. Preliminary notes on the delicacy of the special senses. New York Medical Journal, 40:325, 1884, cited in Doty, R.L. Mammalian Olfaction, Reproductive Processes, and Behavior, 1976.

Bailey, E.H.S. and Powell, L.M. Some special tests in regard to the delicacy of the sense of smell. Transactions of the Kansas Academy of Science, 9:100-101, 1885, cited in Doty, R.L. Mammalian Olfaction, Reproductive Processes, and Behavior, 1976.

Doty, R.L. Chemical Senses, 6:351, 1981.

Doty, R.L. et al., Journal of Comparative Physiological Psychology, 95:45, 1981.

Gilbert, A.N. and Wysocki, C.J., The Smell Survey Results, National Geographic, 122:514-525, 1987.

Koelega, H.S. and Koster, E.P. Some experiments on sex differences in odor perception. Annals of t he New York Academy of Sciences, 237:234-246, 1974, cited in Doty, R.L. Mammalian Olfaction, Reproductive Processes, and Behavior, 1976.

Le Magnen, J. Les phenomenes olfacto-sexuels chex l'homme. Archives des Sciences Physiologiques, 6:125-160, 1952, cited in Doty, R.L Mammalian Olfaction, Reproductive Processes, and Behavior, 1976.

McGuinness, D. Exploring Sex Differences, pp 123-156, 1976.

Schneider and Wolf, R.A. and Wolf, S. Olfactory perception thresholds for citral utilizing a new type olfactorium. Journal of Applied Physiology, 8:337-342, 1955, cited in Doty, R.L. Mammalian Olfaction, Reproductive Processes, and Behavior, 1976.

Toulouse, E. and Vaschide, N. Mesure de l'odorat chex l'homme et chez la femme. Comptes Rendue des Sceances de la Societe de Biologie et de Ses Filiales, 51;381-383, 1899, cited in Doty, R.L. Mammalian Olfaction, Reproductive Processes, and Behavior, 1976.

Wysocki, C.J. and Gilbert, A.N. The National Geographic Smell Survey: Effects of age are heterogenous. Annals of the New York Academy of Sciences, 561:12-28, 1989.