Allergology International. 2009;58:383-388
DOI: 10.2332!allergolint.08-OA-0050
ORIGINAL ARTICLE
Two Thirds of Forest Walkers with
Japanese Cedar Pollinosis Visit
Forests even During the
Pollen Season
Emi Morita1,5, Jun Nagano2, Hirokazu Yamamoto3, Isao Murakawa4,
Mieko Aikawa4 and Taro Shirakawa1,6
ABSTRACT
Background: The most common type of pollinosis in Japan is Japanese cedar pollinosis (JCP). While forest
walking is a common form of recreation for Japanese people, it has been unclear whether forest walkers with
JCP still choose to visit forested areas during the pollen season or whether they avoid those areas, and as
such, the aim of this study was to investigate this question.
Methods: The study participants were all healthy men and women volunteers aged 20 years or over who vis-
ited the Tokyo University Forest in Chiba during 4 different days. The survey was conducted using self-
administered questionnaires.
Results: The number of available responses was 498. Of these, 112 participants who experienced JCP were
included in the analysis. Seventy-three participants (65.2%) responded that they visit forests even during the
pollen season. The association between forest walking choices during the pollen season and self-rated levels
of pollinosis symptoms was not statistically significant (Cramer’s V = 0.13, p = 0.47). As many as 60% of the
participants who reported serious symptom levels responded that they visit forested areas even during the pol-
len season.
Conclusions: These results revealed that two thirds of forest walkers who had experienced JCP visited for-
ests even during the pollen season. This indicates the further need for public service announcements informing
people with JCP that the risk of pollen exposure and subsequent JCP reaction is increased by visiting forested
areas during the pollen season.
KEY WORDS
forest walking, Japanese cedar pollinosis, pollen season, recreation activity, shinrin-yoku
INTRODUCTION
A natural environment is recognized as bolstering
good health in humans. For example, there is a long
tradition of health resort programs in European coun-
tries and Japan, with a natural environment recog-
nized as relevant to such facilities.1 However, when
people visit a natural environment during the pollen
season, it is quite likely that they will encounter aller-
1Graduate School of Medicine, Kyoto University, Kyoto, 2Institute
of Health Science, Kyushu University, Fukuoka, 3Graduate School
of Frontier Sciences, The University of Tokyo, Chiba, 4Graduate
School of Agricultural and Life Sciences, The University of Tokyo,
Tokyo, 5Present address: Nagoya University Graduate School of
Medicine, Aichi and 6Present address: UCG (Universal Clinic
Group), Nagasaki, Japan.
Correspondence: Emi Morita, Ph. D., Department of Preventive
Allergology International Vol 58, No3, 2009 www.jsaweb.jp!
gens such as pollen.
In Japan, forest walking (“shinrin-yoku”) is a popu-
lar recreational activity. According to a public opinion
poll conducted by the Cabinet Office of the Govern-
ment of Japan in 2007, 36.2% of respondents had par-
ticipated in forest walking (“shinrin-yoku”) for recrea-
tion and both mental and physical benefits within the
preceding year.2 Recent studies have revealed the
preferable physiological and psychological effects of
Medicine!Biostatistics and Medical Decision Making, Nagoya Uni-
versity Graduate School of Medicine, 65 Tsurumai-Cho, Showa-
Ku, Nagoya, Aichi 466−8550, Japan.
Email: emorita@med.nagoya−u.ac.jp
Received 1 October 2008. Accepted for publication 24 February
2009.
!2009 Japanese Society of Allergology
383
Morita E et al.
forest walking.3-5 However, approximately 10−20% of
Japanese adults suffer from Japanese cedar pollinosis
(JCP), the most common type of pollinosis in Ja-
pan.6-8 Forests cover 68.2% of the land in Japan, and
forests of mainly Japanese cedar occupy 12% of the
country.9,10 As such, it is quite likely for people to en-
counter Japanese cedar trees when visiting forested
areas. It is recommended that patients with JCP avoid
exposure to pollen during the pollen season.11
Contradictorily, people are recommended to avoid
exposure to pollen during the pollen season, but for-
est walking is still an encouraged activity, and so far
this has not been clearly reversed.11 Before now, it
has been unclear whether forest walkers who are sus-
ceptible to JCP still choose to visit forested areas dur-
ing the pollen season or whether they avoid those ar-
eas, and as such, the aim of this study was to investi-
gate this question.
METHODS
The study participants were healthy male and female
volunteers aged 20 years and over who visited the To-
kyo University Forest in Chiba while it was opened to
the public over 4 different days in November and De-
cember, 2004, and who agreed to participate in the
study. The forest is located deep in a mountainous
area in the middle of Honshu, the main island of Ja-
pan. The forest covers a total area of 2200 hectares
and consists of natural conifers, natural broadleaf
trees, a planted Japanese cedar forest of 500 hectares,
and a planted Japanese cypress forest of 250 hec-
tares.12
The survey was conducted using self-administered
questionnaires. The participants were required to an-
swer questions regarding whether they suffer from
JCP (“yes” or “no”), their usual frequency of visits to
forested areas, and the presence of one or more com-
panions (“none” or “yes”). If the respondents indi-
cated that they experienced JCP, they were also re-
quired to indicate their self-rated level of symptoms
(“serious,” “moderate,” or “slight”), and their choice
whether to visit forests during the pollen season
(“visit forested areas even during the pollen season,”
“avoid visiting forested areas during the pollen sea-
son,” or “rarely visit forested areas”). First, the age,
gender, and usual frequency of visits to forested ar-
eas were compared between the participants without
JCP and the participants with JCP, using a Student’s t-
test and a Chi-squared test. Only the participants who
responded that they had experienced JCP were in-
cluded in the subsequent analysis. The Chi-squared
test was used to evaluate any relevance between self-
rated levels of symptoms and gender, and to evaluate
relevance between self-rated levels of symptoms and
age group. Cramer’s V coefficient was used to evalu-
ate the relevance between the participants’ forest
walking choices during the pollen season and their
usual frequency of visits to forested areas, and to
evaluate the relevance between their forest walking
choices during the pollen season and participants’
self-rated levels of symptoms. A Chi-squared test was
used to evaluate the relevance between forest walk-
ing choices during the pollen season and gender, to
evaluate the relevance between forest walking
choices during the pollen season and age groups
(20−39 years, 40−59 years, and 60+ years), and to
evaluate the relevance between forest walking
choices during the pollen season and the presence of
one or more walking companions on the survey day.
SPSS 14.0J for Windows was used for statistical analy-
ses. Significance level was set at 5%.
The Ethics Committee of Kyoto University ap-
proved the study protocol.
RESULTS
A total of 541 people agreed to participate in the sur-
vey. The number of available responses was 498. Of
these, 112 participants had experienced JCP (22.5% of
the available responses; 55 men and 57 women; mean
age ± SD: 54.6 ± 9.9 years). Nine participants did not
provide information related to their experience of
JCP. The remaining 377 participants had not experi-
enced JCP (187 men and 190 women; mean age ± SD:
56.7 ± 10.8 years). The characteristics of the partici-
pants are presented in Table 1. There were no statisti-
cal differences in the age and ratio of gender between
the participants with JCP and the participants without
JCP. There was also no statistical difference in the
usual frequency of visits to forested areas between
the participants without JCP and the participants with
JCP. The 112 participants with JCP were included in
the subsequent analysis. Among the 112 included
participants, 35 (31.3%) indicated “serious” as their
self-rated level of symptoms, 49 (43.8%) responded
“moderate” and 28 participants (25.0%) responded
“slight.” Associations between self-rated levels of
symptoms and gender, and between self-rated levels
of symptoms and age group are presented in Table 2.
Neither were significant.
Seventy-three participants (65.2%) responded that
they visit forested areas even during the pollen sea-
son, while 32 participants (28.6%) stated that they
avoid visiting forested areas during the pollen season.
Seven participants (6.2%) responded that they rarely
visited forests. As shown in Table 3, the association
between people’s forest walking choices during the
pollen season and their frequency of visits to forested
areas was statistically significant at a middle level
(Cramer’s V = 0.35, p < 0.001). The higher the usual
frequency of visits to forested areas, the higher the
rate of visiting forested areas even during the pollen
season. To further explore factors that may affect the
decision of visiting forested areas by regular forest-
walkers with JCP, we examined, using a Chi-squared
test, several properties of participants who visit for-
ested areas once a month or more (n = 47) in associa-
384
Allergology International Vol 58, No3, 2009 www.jsaweb.jp!
Forest Walkers with Pollinosis
Table1 CharacteristicsofparticipantswithandwithoutJapanesecedarpollinosis(JCP)
WithJCP
WithoutJCP
Statisticaltest
Mean age (years)
54.6±9.9
Total(n)
112(100.0%)
Male
55(49.1%)
Female
57(50.9%)
Frequencyofvisitstoforestedareas(n)
More than once a month
27(24.1%)
Once a month
20(17.9%)
Severalperyear
43(38.4%)
Onceayearorless
22(19.6%)
a:Chi-squaredtest;b:Student’st-test.
56.7±10.8
377(100.0%)
187(49.6%)
190(50.4%)
85(22.5%)
80(21.2%)
151(40.1%)
58(15.4%)
t(486)＝ 1.8,p＝ 0.07
b
χ2＝ 0.008,df＝ 1,p＝ 0.9 a
χ2＝ 2.8,df＝ 3,p＝ 0.4
a
Table2 Associationbetweenself-ratedlevelofsymptomsandsex,andbetweenself-ratedlevelofsymptomsandage
Sex
Male
Female
Serious
n
%
18 32.7
17 29.8
Moderate
n
%
24 43.6
25 43.9
Slight
n
%
13 23.6
15 26.3
Total
n
%
55
100
57
100
Chi-squared test
P＝ 0.9
χ2＝ 0.2,df＝ 2
Age(years) 20― 39
40― 59
60＋
3 27.3
6 54.5
2 18.2
11
100 P＝ 0.7
21 35.6
25 42.4
13 22.0
59
100 χ2＝ 2.1,df＝ 4
11 26.2
18 42.9
13 31.0
42
100
tion with their forest walking choices during the pol-
len season. However, we could not find a statistically
significant association for the factors including gen-
der, age, job, self-rated level of symptoms, health
practices (smoking, drinking alcohol, breakfast hab-
its, and exercise), self-rated overall health condition,
and perceived mental stress (data not shown).
Next, the association between people’s forest walk-
ing choices during the pollen season and their self-
rated level of symptoms is presented in Table 3; the
association was weak and statistically non-significant
(Cramer’s V = 0.13, p = 0.47). Even in the subgroup
who reported a serious level of symptoms, as many as
60% of the participants responded that they visit for-
ested areas even during the pollen season. The asso-
ciation between forest walking choices during the
pollen season and their gender was not statistically
significant (χ2 = 1.6, df = 2, p = 0.5), although 70.9% (n
= 39) of men and 59.6% (n = 34) of women responded
that they visit forested areas even during the pollen
season. The association between people’s age and
their forest walking choices during the pollen season
is shown in Table 3. Fifty-four point five percent (n =
6) of the participants aged 20 to 39 years, 62.7% (n =
37) of those aged 40 to 59 years, and 71.4% (n = 30) of
those aged 60+ years responded that they visit for-
ested areas even during the pollen season. The
higher their age, the higher was their rate of visiting
forested areas even during the pollen season. How-
ever, there was no statistical difference between peo-
ple’s forest walking choices during the pollen season
and their age (3 groups) (χ2 = 3.4, df = 4, p = 0.6). A
total of 84.6% (n = 11) of the participants who came to
the forest alone on the survey day responded that
they visit forested areas even during the pollen sea-
son, while 62.6% (n = 62) of the participants who came
to the forest with one or more walking companions
on the survey day responded that they visit forested
areas even during the pollen season. However there
was no statistical difference between people’s forest
walking choices during the pollen season and the
presence of one or more walking companions (χ2 =
2.7, df = 2, p = 0.3).
DISCUSSION
The forested area where the survey took place in this
study occupies 31% of Chiba Prefecture. The Japa-
nese cedar area occupies approximately 30% of this
forested area.13 Japanese cypress pollen is also re-
leased in the spring, following the dispersion of Japa-
nese cedar pollen, which is mainly from February to
April. The peak season for Japanese cedar pollen in
the Chiba area is March. An example of the preva-
lence of cedar pollen in Japan is that the Japan Minis-
try of the Environment noted that in March 2005, in
Chiba Prefecture, the average total concentration of
Japanese cedar pollen and Japanese cypress pollen at
three residential area survey points during one hour
was 64.8−137.2 grains!m3 monitored with real-time
pollen monitors.14,15 However, the same monitoring
at two mountain area survey points were 234.3
grains!m3 and 534.1 grains!m3, respectively.16 These
figures indicate that Japanese cedar pollen tends to
be scattered more in mountain areas than in towns.
Allergology International Vol 58, No3, 2009 www.jsaweb.jp!
385
Morita E et al.
Table3 Associationbetweenforestwalkingchoicesduringthepollenseasonandfrequencyofvisitstoforestedareas,self-
ratedlevelsofpollinosissymptoms,andage,respectively
Frequency
of visits to
forested
areas
More than
once a month
Once a month
Severalper
year
Once a year
or less
Total
Self-rated
symptoms
Serious
Moderate
Slight
Total
Age (years)
20― 39
40― 59
60＋
Total
Visit
forests
n
23
%
85.2
n
14
%
70.0
n
29
%
67.4
n
7
%
31.8
n
73
%
65.2
n
21
%
60.0
n
31
%
63.3
n
21
%
75.0
n
73
%
65.2
n
6
%
54.5
n
37
%
62.7
n
30
%
71.4
n
73
%
65.2
Forestwalkingchoicesduringthepollenseason
Avoid
Rarely ever
visitingforests visitforests
Total
4
14.8
6
0
27
0.0
100.0
0
20
30.0
13
30.2
0.0
100.0
1
43
2.3
100.0
9
40.9
32
6
27.3
7
22
100.0
112
28.6
13
6.3
100.0
1
35
37.1
14
2.9
100.0
4
49
28.6
5
17.9
8.2
100.0
2
28
7.1
100.0
32
28.6
4
7
112
6.3
100.0
1
11
36.4
17
28.8
9.1
100.0
5
59
8.5
100.0
11
26.2
32
1
42
2.4
100.0
7
112
28.6
6.3
100.0
StatisticalTest
Cramer’s
V＝ 0.35
P＜ 0.001
Cramer’s
V＝ 0.13
P＝ 0.47
χ2＝ 3.4
df＝ 4
P＝ 0.6
Nevertheless, this present survey shows that as
many as two thirds of forest walkers who are suscep-
tible to JCP choose to visit forested areas even during
the pollen season. The most significant factor was the
usual frequency of visits to forested areas. More than
85% of heavy forest walkers, those who go to forested
areas more than once a month (n = 23), responded
that they visit forested areas during the pollen sea-
son. Since it may be a lifestyle choice for heavy forest
walkers to visit forested areas as they feel particular
enjoyment when doing so, it might be difficult to ef-
fectively discourage them from visiting forested areas
during the pollen season. They might choose the
pleasant feelings from visiting forested areas over the
discomfort of JCP. However, forest walkers who fre-
quently visit forested areas during the pollen season
will occupy the highest risk groups for these pollino-
sis symptoms because of the greater chance of expo-
sure to Japanese cedar pollen in forested areas.
The rate of visiting forested areas during the pollen
season was higher (although not significant) among
the participants aged 60+ years, male participants,
participants who visited the forest alone, and partici-
pants who had only slight symptoms. The partici-
pants with slight symptoms may visit forested areas
more often because their discomfort is not high.
However, the association between people’s forest
walking choices during the pollen season and their
self-rated level of symptoms is weak; in the serious-
symptom subgroup, as many as 60% of the partici-
pants responded that they visit forested areas even
during the pollen season.
Considering these results, since visiting forested
areas increases the risk of exposure to Japanese ce-
dar pollen, we recommend further clarification
through public announcements of the risk of increas-
ing one’s exposure to the allergenic pollen by visiting
forested areas during the pollen season. This infor-
mation should be aimed at forest walkers with JCP,
especially those who are heavy forest walkers. The
content of the announcements should contain the fol-
lowing information: Forest walkers who experience
JCP should not go into forested areas during the pol-
len season. Instead they should choose specific for-
386
Allergology International Vol 58, No3, 2009 www.jsaweb.jp!
Forest Walkers with Pollinosis
ested areas that are far away from Japanese cedar pol-
len sources, or if they choose to visit forested areas
that contain Japanese cedar pollen, they should use
special protective equipment.
There are Japanese cedar trees in the University
Forest, but the survey was conducted in late autumn,
outside the pollen season. Therefore, at the time of
the survey, participants were not afflicted with JCP.
Because this survey was conducted at the Tokyo Uni-
versity Forest, which is not easily accessible by pub-
lic transportation, we regarded the survey partici-
pants as particularly enthusiastic forest walkers.
Therefore, the participants may not be representative
of the general population. Furthermore, the partici-
pants, with a mean age in the fifth decade, were older
than the general population. There is a possibility
that the results in this study would be different from
that in a younger or more general population with
pollinosis.
This study has some limitations. First, the sample
size was not very large, especially for exploring fac-
tors that may affect regular forest-walkers’ decision of
visiting forested areas despite of their JCP. We could
not find a significant factor among demographic, life-
style, job-related, and health-related factors, but this
may be due to the insufficient sample size. This issue
is important in making further concrete recommenda-
tions to regular forest-walkers, and needs to be ad-
dressed by future studies with a larger number of
subjects. Second, the participants’ level of pollinosis
symptoms was self-rated and approximate, as op-
posed to a diagnosis by medical doctors or standard-
ized estimations. As such, there may be a problem
with the reliability and validity of the reported levels
of pollinosis symptoms. Third, pollinosis can be con-
siderably controlled using strong medications that
have been recently developed, such as nose drops
with corticosteroids. Some of the participants in this
survey may have used such medications during the
pollen season. With the result of being free from polli-
nosis symptoms, such people’s forest walking choices
during the pollen season may be affected. However,
this survey did not collect any information regarding
the treatment of pollinosis. Fourth, this study did not
ask why patients with JCP choose to visit forested ar-
eas even during the pollen season. It is presumed
that they might focus more on the pleasant feeling or
well-being that comes from walking in forested areas
over the uncomfortable symptoms of pollinosis. Or
they might not recognize that there is a greater risk
of exposure to high concentrations of antigens when
visiting forested areas. In future studies with a suffi-
ciently larger sample size, a high variability scale for
the level of pollinosis symptoms should be used, and
information regarding participants’ treatment of polli-
nosis and their motives for visiting forested areas
should be obtained, as these factors require further
consideration. The merits or risks of choosing to visit
forested areas during the pollen season, as consid-
ered by forest walkers with JCP, should also be inves-
tigated in future studies.
In conclusion, this study revealed that two thirds of
forest walkers who had experienced JCP choose to
visit forested areas even during the pollen season.
This was despite the recommendation that those sus-
ceptible to JCP avoid exposure to pollen. This indi-
cates the further need for public service announce-
ments informing people with JCP, especially those
who are heavy forest walkers, that the risk of pollen
exposure and subsequent JCP reaction is increased
by visiting forested areas during the pollen season.
ACKNOWLEDGEMENTS
The authors would like to thank the staff of the Tokyo
University Forest, Chiba, as well as the Forest In-
structor Association, Chiba, for their cooperation in
collecting data for this study.
REFERENCES
1. Morita E, Weigl M, Schuh A, Stucki G. Identification of
relevant ICF categories for indication, intervention plan-
ning and evaluation of health resort programs: a Delphi
exercise. Int J Biometeorol 2006;50:183-91.
2. Cabinet Office of Government of Japan. [The Opinion Poll
on Forests and Life 2007]. Tokyo: Cabinet Office of Gov-
ernment of Japan, 2007 (in Japanese).
3. Ohtsuka Y, Yabunaka N, Takayama S. Shinrin-yoku
(forest-air bathing and walking) effectively decreases
blood glucose levels in diabetic patients. Int J Biometeorol
1998;41:125-7.
4. Ohira H, Takagi S, Masui K, Oishi M, Obata A. [Effects
on shinrin-yoku (forest-air bathing and walking) on men-
tal and physical health]. [Bull Tokai Women Univ] 1999;
19:217-32 (in Japanse).
5. Morita E, Fukuda S, Nagano J et al. Psychological effects
of forest environments on healthy adults: Shinrin-yoku
(forest-air bathing, walking) as a possible method of
stress reduction. Public Health 2007;121:54-63.
6. Okuda M. Epidemiology of Japanese cedar pollinosis
throughout Japan. Ann Allergy Asthma Immunol 2003;91:
288-96.
7. Sakurai Y, Nakamura K, Teruya K et al. Prevalence and
risk factors of allergic rhinitis and cedar pollinosis among
Japanese men. Prev Med 1998;27:617-22.
8. Kaneko Y, Motohashi Y, Nakamura H, Endo T, Eboshida
A. Increasing prevalence of Japanese cedar pollinosis: a
meta-regression analysis. Int Arch Allergy Immunol 2005;
136:366-71.
9. Food and Agriculture Organization of the United Nations.
State of the World’s Forests, 2007. Rome: Food and Agri-
culture Organization of the United Nations, 2007;111.
10. Statistics Department, Minister’s Secretariat, Ministry of
Agriculture, Forestry and Fisheries, Japan. [The Statisti-
cal Yearbook of the Ministry of Agriculture, Forestry and
Fisheries, Japan]. Tokyo: Statistical Department, Minis-
ter’s Secretariat, Ministry of Agriculture, Forestry and
Fisheries, Japan, 2005;378-9 (in Japanese).
11. Baba K, Konno A, Takenaka H et al. (eds). [Practical
Guideline for the Management of Allergic Rhinitis in Ja-
pan]. Tokyo: Life Science, 2005;20 (in Japanese).
12. The Tokyo University Forests. [Outline of University For-
Allergology International Vol 58, No3, 2009 www.jsaweb.jp!
387
Morita E et al.
est in Chiba]. Tokyo: The Tokyo University Forests, 2008;
3 (in Japanese).
13. Forestry Division Office, Agriculture, Forestry and Fish-
eries Department, Chiba Prefectural Government. [2006
Annual Report on Forests and Forestry]. Chiba: Chiba Pre-
fectural Government, 2007;22 (in Japanese).
14. Takahashi Y, Kawashima S, Fujita T, Ito C, Togashi R,
Takeda H. [Comparison between real-time pollen monitor
KH-3000 and Burkard sampler]. Arerugi 2001;50:1136-42
(in Japanese).
15. Imai T, Nohara O, Endo T, Fukaya S. [Usefulness and
practical use of an automatic counter for scattering pollen
in spring]. Arerugi 2005;54:559-68 (in Japanese).
16. Ministry of the Environment, Japan. [The Pollen Distribu-
tion Situation in the 2004-2005 Fiscal Year]. Tokyo: Min-
istry of the Environment, 2005;1-19 (in Japanese).
388
Allergology International Vol 58, No3, 2009 www.jsaweb.jp!