Lower olfactory threshold during the ovulatory phase of the menstrual cycle

Abstract

We investigated whether olfactory detection threshold is correlated with phase of the menstrual cycle. Three hundred and thirty-two women 13-49 years old were tested once during either the follicular, ovulatory, luteal or menstrual phase, and 15 women 20-43 years old were tested at each of these phases across one complete cycle. In three non-cycling control groups subjects were each tested once; 83 post-menopausal women 47-86 years old, 60 pre-pubertal girls 5-12 years old, and 183 men 17-30 years old. Odor detection thresholds were determined using sniff bottles containing -log9.5 to -log6.0 concentrations of amyl acetate presented in ascending order. Thresholds differed significantly across the cycle and were lowest during the ovulatory and highest during the menstrual phase. Thresholds for all control groups were higher than for the cycling women during the ovulatory phase. The results confirm that olfactory threshold is related to phase of the menstrual cycle and thus possibly to hormonal state.

Full text

Lower olfactory threshold during the ovulatory
phase of the menstrual cycle
Evelia Navarrete-Palacios
a,b
, Robyn Hudson
c
, Gloria Reyes-
Guerrero
b
, Rosalinda Guevara-Guzma´n
b,
*
a
Hospital Central Militar, Ciudad de Me´xico, Instituto de Investigaciones Biome´dicas, Universidad Nacional
Auto´noma de Me´xico, 04510 Mexico, D.F., Mexico
b
Departamento de Fisiologı´a, Facultad de Medicina, Instituto de Investigaciones Biome´dicas, Universidad
Nacional Auto´noma de Me´xico, Apartado Postal 70250, 04510 Mexico, D.F., Mexico
c
Departamento de Biologı´a Celular y Fisiologı´a, Instituto de Investigaciones Biome´dicas, Universidad
Nacional Auto´noma de Me´xico, 04510 Mexico, D.F., Mexico
Received 15 November 2002; accepted 8 April 2003
Abstract
We investigated whether olfactory detection threshold is correlated with phase of the
menstrual cycle. Three hundred and thirty-two women 13 /49 years old were tested once
during either the follicular, ovulatory, luteal or menstrual phase, and 15 women 20 /43 years
old were tested at each of these phases across one complete cycle. In three non-cycling control
groups subjects were each tested once; 83 post-menopausal women 47 /86 years old, 60 pre-
pubertal girls 5/12 years old, and 183 men 17/30 years old. Odor detection thresholds were
determined using sniff bottles containing 
/log 9.5 to /log 6.0 concentrations of amyl acetate
presented in ascending order. Thresholds differed significantly across the cycle and were
lowest during the ovulatory and highest during the menstrual phase. Thresholds for all control
groups were higher than for the cycling women during the ovulatory phase. The results
confirm that olfactory threshold is related to phase of the menstrual cycle and thus possibly to
hormonal state.
#2003 Elsevier B.V. All rights reserved.
Keywords: Olfactory sensitivity; Hormonal state; Men; Girls; Post-menopause
* Corresponding author. Tel.: 
/525-550-3587; fax: /525-623-2241.
E-mail address: rguevara@servidor.unam.mx (R. Guevara-Guzma´n).
Biological Psychology 63 (2003) 269 /279
www.elsevier.com/locate/biopsycho
0301-0511/03/$ - see front matter #2003 Elsevier B.V. All rights reserved.
doi:10.1016/S0301-0511(03)00076-0

1. Introduction
Olfactory researchers have long been interested in a possible relationship between
olfactory function and the menstrual cycle, and particularly as indicated by changes
in odor detection threshold. At present, the weight of evidence suggests increased
sensitivity, at least for some substances, around the time of ovulation and/or the
mid-luteal phase (Le Magnen, 1952; Vierling and Rock, 1967; Mair et al., 1978; Doty
et al., 1981, 1982), including as measured by olfactory reaction time (Narita et al.,
1992) and event-related potentials (Pause et al., 1994, 1996). Some investigators,
however, have reported increased sensitivity during the follicular phase (Henkin,
1974), or around menses (Ko
¨ster, 1968; Doty, 1976), while still others have reported
decreased sensitivity at menstruation (Le Magnen, 1952; Schneider and Wolf, 1955;
Good et al., 1976; Mair et al., 1978; Moriyama and Kurahashi, 2000), or have failed
to find reliable, cycle-dependent changes in olfactory sensitivity (Amoore et al., 1975;
Herberhold et al., 1982; Filsinger and Monte, 1986; Hummel et al., 1991; Kanamura
and Takashima, 1991), including in olfactory event-related potentials (Nghiemphu et
al., 1995).
Such discrepancies may be at least partly explained by differences in methodology
among studies, including the small sample sizes sometimes used and differences in
the time points of the cycle taken for comparison. Interpretation of findings is also
made difficult in some cases by the lack of parallel testing of non-cycling control
groups. In the present study it was therefore our aim to investigate the relationship
between the menstrual cycle and olfactory threshold by testing a large sample of
cycling women not taking oral contraceptives, together with three non-cycling
control groups*/post-menopausal women, pre-pubertal girls and young men.
2. Methods
The study proposal and test procedures were approved by the ethics committees of
the Faculty of Medicine, National University of Mexico, and the Central Military
Hospital, Mexico City. Subjects, or in the case of the girls, their parents, were
informed as to the purpose of the study before obtaining their voluntary consent to
participate.
2.1. Definition of the menstrual cycle
This was defined as the time between the first day of one menstruation and the
first day of the next, with the first day of menstrual bleeding taken as day 1. The
menstrual phase was defined as cycle days 1/5, the follicular or estrogenic phase as
days 6/14, and the luteal or progestagenic phase as days 15/28 or beyond. The
menstrual phase was defined in a uniform manner because of uncertainty as to the
exact length of menstruation for each of the large number of women recruited at
different stages of the cycle in Group 1 (see below). As described for Groups 1 and 2
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below, the ovulatory phase was defined as the day midcycle when basal temperature
rose by at least 0.3 8C.
2.2. Subjects
Participants were recruited from the campus of the National University and from
the Military Hospital. All were healthy, non-smoking residents of Mexico City, none
was taking medication and none had used oral contraceptives for at least 6 months
prior to the start of the study. Subjects were instructed not to use perfumed toiletries
on the day of the experiment and not to drink alcohol or coffee or to eat garlic,
onions or other spicy foods the day before. The following groups were formed (Table
1).
2.2.1. Group 1
Three hundred and thirty-two regularly cycling women 13 /49 years old whose
cycles ranged from 28 to 30 days (mean 28.8, SD 0.3) tested once during one of the
four principle phases of the menstrual cycle */menstrual, follicular, ovulatory or
luteal. To obtain subjects for testing during the ovulatory phase, women recruited
close to midcycle were instructed to take their oral temperature at the same time each
morning, to enter the values on a score sheet, and to report for olfactory testing
when their temperature rose by at least 0.3 8C. Only subjects adhering strictly to the
measuring regimen and showing a clear rise in temperature were included in this,
consequently small, category.
2.2.2. Group 2
Fifteen regularly cycling women 20 /43 years old whose cycles ranged from 28 to
30 days (mean 29, SD 0.3) tested at each of the four principle phases of one
menstrual cycle*/menstrual, follicular, ovulatory, and luteal. For five women testing
started in the menstrual phase, for four women in the follicular, for two in the
ovulatory, and for four in the luteal phase. As for Group 1, subjects were instructed
Table 1
Composition of the experimental groups according to age
Groups NMean age in years (SD) Age range in years
Cycling women tested once 332 22.1 (4.7) 13 /49
Menstrual phase 87 23.6 (4.8) 13 /49
Follicular phase 80 22.6 (4.7) 13 /45
Ovulatory phase 21 22.7 (4.7) 13 /43
Luteal phase 144 22.3(4.7) 14 /49
Cycling women tested repeatedly 15 26.2 (5.5) 20 /43
Post-menopausal women 83 67.4 (8.2) 47 /86
Pre-pubertal girls 60 8.3 (2.8) 5 /12
Young men 183 21 (4.5) 17 /30
Navarrete-Palacios et al., 2003.
E. Navarrete-Palacios et al. / Biological Psychology 63 (2003) 269/279 271

to take their oral temperature at the same time each morning, to enter the values on a
score sheet, and to report for olfactory testing when their temperature rose by at
least 0.3 8C.
2.2.3. Group 3
Eighty-three post-menopausal women 47 /86 years old, at least 6 months after the
last menstruation, tested once.
2.2.4. Group 4
Sixty pre-pubertal, non-menstruating girls 5 /12 years old, tested once.
2.2.5. Group 5
One hundred and eighty-three men 17 /30 years old, tested once.
2.3. Test procedure
Testing was carried out in a quiet room at the Military Hospital between 10:00 and
13:00 h. Subjects were seated in a comfortable chair at a room temperature of 18/
22 8C.
In a first step, designed to obtain a rough estimate of each subject’s sensitivity so
as to reduce the number of concentrations presented in the subsequent finer
determination of threshold, subjects were presented with an ascending series of eight
concentrations of amyl acetate (J.T. Baker, Mexico) in 100 ml polyethylene squeeze
bottles equipped with a fine plastic nozzle and containing a 30 ml solution of the
odorant in distilled water. Based on pilot testing, the concentrations we used ranged
from 
/log 9.5 to /log 6.0 presented in ascending half log concentrations. Subjects
were asked to hold each bottle under their nose, to squeeze it gently, and to respond
with yes or no according to whether they detected an odor or not. They were only
allowed to sample the content of each bottle once and with an interval of at least 45 s
between bottles. Amyl acetate was chosen because of its frequent use in olfactory
studies, because it is generally agreeable, readily available, soluble in water, and
because its smell resembles banana and so might be considered familiar and easy to
detect for the population tested.
In a second step, a finer estimate of detection threshold was obtained by
presenting an ascending series of concentrations using a four-alternative forced-
choice procedure (cf. Koelega and Ko
¨ster, 1974; Koelega, 1994). Subjects were
presented with a set of four bottles, two of which contained amyl acetate one dilution
step below the concentration the subject had detected previously, and two which
contained 30 ml distilled water. Subjects were asked to identify the two bottles that
contained the odorant, the probability of achieving this by chance being only 17%
compared to 33% in the commonly used three-bottle forced-choice test. If a mistake
was made the procedure was repeated using the next highest concentration. If no
mistake was made we took this value as the threshold. The results of this second test
were used for the analyses presented below.
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2.4. Statistical analysis
To compare thresholds of the cycling women of Group 1 tested once at different
phases of the menstrual cycle the Kruskal /Wallis non-parametric ANOVA for
ranks was used followed by post hoc Dunn’s tests. To compare thresholds of the
cycling women of Group 2, each tested at four phases of the cycle, a non-parametric
Friedman ANOVA for repeated measures was used followed by post hoc Student /
Newman/Keuls tests. To compare the threshold values during ovulation of the
cycling women of Group 1 with the threshold values of the post-menopausal women
of Group 3, the pre-menstrual girls of Group 4, and the men of Group 5, non-
parametric Mann/Whitney Utests were used. For all tests a two-tailed avalue of
0.05 was taken as the level of significance.
3. Results
Fig. 1 shows the detection thresholds for amyl acetate for the 332 women of
Group 1 tested at different phases of the menstrual cycle. Detection thresholds
differed significantly across the cycle, with a median of 
/log 7.0 (range 6.0 /8.5)
during the menstrual phase, a median of 
/log 7.5 during the follicular and luteal
phases (ranges 6.05/9.5 and 6.0/9.0, respectively), and of /log 8.5 (range 6.0 5/9.5)
during the ovulatory phase (Kruskal /Wallis ANOVA; H/18.4, df/3, PB/0.001).
Fig. 1. Box plots of odor detection thresholds for amyl acetate for the 332 women of Group 1 tested at one
of four phases of the menstrual cycle; menstrual N/87, follicular N/80, ovulatory N/21, and luteal
N/144. Horizontal lines represent the 10th, 25th, 50th (median), 75th and 90th percentiles. *PB/0.05,
Dunn’s post hoc tests.
E. Navarrete-Palacios et al. / Biological Psychology 63 (2003) 269/279 273

Thresholds recorded during the ovulatory phase were significantly lower compared
to the menstrual and luteal phases, and the follicular compared to the menstrual
phase (Dunn; PB/0.05).
As shown in Fig. 2, detection thresholds for amyl acetate also differed significantly
across the menstrual cycle for the repeatedly tested women of Group 2 (Friedman
repeated measures ANOVA; x
2
-value/39.6, df/3, PB/0.001). A significantly
lower median threshold of 
/log 9.0 (range 8.5 5/9.5) was recorded during the
ovulatory phase compared to the threshold of 
/log 8.5 recorded during the
menstrual (range 7.5/9.0), follicular (range 8.0/9.0) and luteal phases (range 7.5 /
8.5) (Student/Newman/Keuls; PB/0.05). Although the threshold scores recorded
for these women were lower than those for Group 1, the overall pattern was similar,
that is, the lowest thresholds were recorded at the time of ovulation.
As shown in Fig. 3, the median detection threshold of the women of Group 1 at
ovulation was significantly lower than that of the post-menopausal woman of Group
3(
/log 8.5, range 6.0 5/9.5 vs/log 7.0, range 6.0 /9.0, respectively; Mann/
Whitney; U/322, N
1
/21, N
2
/83, PB/0.001), and the girls of Group 4 (/
log 8.5 vs/log 7.0, range 6.0 /9.0; Mann/Whitney, U/336, N
1
/21, N
2
/60,
PB/0.002). Thresholds were also lower than for the men of Group 5 (/log 8.0,
range 6.0/9.0) although not significantly so (Mann/Whitney, U/1535, N
1
/21,
N
2
/183, P/0.10).
4. Discussion
The present findings are consistent with those of previous studies reporting greater
olfactory sensitivity of women during the ovulatory phase of the menstrual cycle (Le
Fig. 2. Box plots of odor detection thresholds for amyl acetate of the women of Group 2 (N/15) tested
repeatedly across one menstrual cycle. Data are presented as for Fig. 1.*PB/0.05, Student /Newman/
Keuls post hoc tests.
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Magnen, 1952; Vierling and Rock, 1967; Mair et al., 1978; Doty et al., 1981, 1982;
Pause et al., 1994), and with reports of a late follicular or midcycle increase in
sensitivity in other sensory modalities (reviewed in Henkin, 1974; Doty et al., 1981,
1982; Brown, 1983; Doty, 1986). Thus, significantly lower detection thresholds for
amyl acetate were recorded at the time of ovulation and, at least in the large sample
of Group 1 women, the highest thresholds were recorded during menstruation.
Indeed, sensitivity at ovulation was probably even greater than represented here
given, as seen in Figs. 1 and 2, that during this phase some women could already
detect the odorant at the lowest concentration presented. Although most subjects
were tested only once and with only one substance, we consider the findings reliable
for several reasons.
The 332 women of Group 1 represent an unusually large sample compared to
earlier studies. As has been noted by previous investigators (Nghiemphu et al., 1995;
Pause et al., 1996), differences between individuals in the ability to perceive
particular odorants or in their response to the test situation may give rise to
spurious effects if sample size is small. This may partly explain the inconsistent
findings among previous reports, some of which, as mentioned in Section 1, were
based on very small samples. The large sample used here, however, made it
impracticable to test more than one odorant or to monitor individual subjects by
repeated testing across one or more cycles (cf. Henkin, 1974; Doty et al., 1981).
Fig. 3. Box plots of odor detection thresholds for amyl acetate of the cycling women of Group 1 during
the ovulatory phase (N/21), of the post-menopausal women (N/83), the pre-pubertal girls (N/60),
and the men (N/183). Data are presented as for Fig. 1.**PB/0.001, ***PB/0.0001, Mann/Whitney U
tests.
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Nevertheless, the 15 women of Group 2 tested repeatedly across the cycle in an
effort to counter the problem of single testing in Group 1, gave the same main
result*/significantly greater sensitivity around the time of ovulation. In accounting
for the lower variance and lower threshold scores of these women compared to those
of Group 1 (Figs. 1 and 2), it may be noted that the Group 2 women formed a
particularly homogeneous sample. All were military personnel living in barracks and
so were subject to the same regular daily regimen and diet and were familiar with the
test premises. The learning or practice effects noted by several authors to occur with
repeated testing (Rabin and Cain, 1986; Laska and Hudson, 1991) may also partly
explain these women’s better overall performance, although given that they were
recruited and testing started at different stages of the cycle this cannot explain their
lower thresholds during the ovulatory phase.
The specificity of the finding of higher sensitivity around the time of ovulation is
also supported by the fact that the threshold scores for the three, in several respects
very different control groups of post-menopausal women, pre-pubertal girls and
young men were all higher than the scores obtained during ovulation for the
comparable Group 1 women who were also tested only once. Age alone would not
seem to account for the greater sensitivity of cycling women around ovulation given
their lower thresholds compared to their age peers in Group 1 tested at other phases,
or to themselves (Group 2) when tested at other phases.
And finally, although the sniff-bottle technique and the simple procedure of
ascending concentrations used here have their shortcomings such as lack of control
over the precise quantity of odorant delivered to subjects per sniff, we consider them
adequate for our purpose since we were not interested in absolute sensitivity per se
and systematic errors of methodology should have affected the performance of the
groups in a similar fashion. Furthermore, sniff bottles have the advantage that
subjects can use their own natural mode of stimulus application and sniffing, and
have been repeatedly shown to generate stable and reproducible measures of
olfactory sensitivity (Laska and Hudson, 1991).
In summary, it seems clear that olfactory sensitivity varies across the menstrual
cycle, with the most consistent change represented by a decrease in threshold around
the time of ovulation. Nevertheless, assuming this is correct how is it to be explained?
An obvious possibility mentioned by several investigators (Le Magnen, 1952;
Schneider et al., 1958; Henkin, 1974; Good et al., 1976) is that it is due to changes in
the level of gonadal steroids, particularly estrogen. Since these hormones or their
receptors have been found in the olfactory epithelium, olfactory bulb, and other
olfactory-related brain areas in several mammalian species (Stumpf and Sar, 1982;
Vannelli and Balboni, 1982; Kratskin, 1995; Zhong et al., 2001), and we have
recently reported cytological changes in the nasal epithelium across the menstrual
cycle paralleling those in the vagina (Navarrete-Palacios et al., 2003), changes in
hormone levels could conceivably influence olfactory function both peripherally and
centrally. Arguing against such a hormonal explanation, however, are findings that
women taking the contraceptive pill also show changes in olfactory threshold across
the cycle (Doty et al., 1981, 1982), that replacement therapy with estrogen has no
effect on olfactory sensitivity in post-menopausal women (Hughes et al., 2002), and
E. Navarrete-Palacios et al. / Biological Psychology 63 (2003) 269/279276

that in the present study the three hormonally different control groups did not differ
significantly in their detection thresholds for amyl acetate. Thus, although the
gonadal steroids do not exhaust the list of neurochemically active substances which
could have cycle-dependent effects on olfactory function (Doty et al., 1981; Stumpf
and Sar, 1982; Doty, 1986; Pause et al., 1996; Compagnone and Mellon, 2000), we
still lack an adequate explanation of the processes underlying these changes.
Nor is it clear what, if any, is the biological significance of such changes.
Suggestions that increased olfactory sensitivity at ovulation might facilitate mate
finding or mate choice (Doty, 1974; Henkin, 1974; Benton, 1982; Grammer, 1993;
Gangestad and Thornhill, 1998; Pause et al., 1999) so far lack firm empirical
support, although reports that women can chose among the odors of men based on
small differences in the degree of match between their own and the donors’ human
leukocyte antigen alleles and in a manner consistent with enhanced immunocompe-
tence of their offspring, lends tantalizing support to this idea (Wedekind et al., 1995;
Wedekind and Fu
¨ri, 1997; Jacob et al., 2002). More parsimoniously, however, it
remains possible that changes in perceptual performance across the menstrual cycle
are simply a (presumably harmless) by-product of other, more fundamental aspects
of reproductive physiology. But even given this later possibility, the phenomenon
remains of interest in at least two respects */as a factor to be taken into account in
olfactory testing, and as an indicator, as in other sensory modalities, of so far
unexplained fluctuations in the central nervous function of cycling women.
Acknowledgements
We thank Olga Alejandra Donatti for technical support, Alejandro Domı´nguez
for help with the figures, Carolina Rojas Castan
˜eda for bibliographical assistance,
and the Hospital Central Militar for providing the facilities for conducting the tests.
The project was supported by grants from CONACyT (25193-N) and DGAPA
(IN209999).
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