Japanese Cedar Pollinosis (スギ花粉症)

Japanese cedar pollinosis is a form of hay fever caused by pollen of the Cryptomeria japonica (Japanese cedar) tree. It is the most prevalent form of hay fever in Japan where it affects 15% of the population. The number of Japanese cedar pollinosis sufferers rises sharply between the months of February and April when Japanese cedar pollen is dispersed in Japan.

On the other hand, there are fewer cases of hay fever triggered by Japanese cedar pollen in Europe and North America where there are few Japanese cedar trees. However, it is often stated that Japanese cedar pollen is a cause of hay fever in Europe and North America where there would not expected to be any Japanese cedar trees. It can be suggested that one reason for this is the translation of the Japanese word "sugi" as "cedar" as opposed to "Japanese cedar." Cedar is actually a conifer related to the Japanese cypress and pine trees.
(For example, the western red cedar is a species in the Thuja genus of the Cupressaceae family.)

Along with European poaceous pollen hay fever and North American ragweed pollen hay fever, it is one of the three most prevalent forms of pollinosis worldwide.

History of Japanese Cedar Pollinosis

It is said that hay fever did not use to exist in Japan but Hidenari ARAKI reported ragweed pollen hay fever in 1961. Following this, Yozo SAITO reported Japanese cedar pollinosis in 1963 and published a paper entitled 'Discovery of Japanese Cedar Pollinosis in Nikko, Tochigi Prefecture' in 1964.

Origin of Japanese Cedar Pollinosis

Japanese cedar pollinosis was thought to be a condition particular to Japan. However, in recent years it has been considered that Cryptomeria fortunei trees found in parts of China are very closely related to or are the same species as the Japanese cedar. Evidence cited for this is the fact that patients suffering from Cryptomeria fortunei hay fever have also been observed in Japan and observations of Japanese cedar pollinosis patients in whom an allergic reaction is elicited by Cryptomeria fortunei pollen.

Dispersion of Japanese Cedar Pollen

Japanese cedar pollen measures between 25-35µm and is dispersed over great distances by the wind. It has been known to be carried distances of over 10km, and in some cases over 300km. However, the pollen count varies depending on topography. For example, large quantities of pollen are said to be distributed throughout Japan's Kanto Plain regardless of which direction the wind blows from due to the fact that the region is surrounded by mountains. Pollen is generally not dispersed over areas located beside the sea when onshore winds are blowing.


It is known that in years following the dispersal of large amounts of pollen, patients do not merely exhibit mild symptoms even in the event that the airborne pollen level in that year itself is relatively low. The number of patients attending hospital is also greater than would be expected from the airborne pollen level. This is thought to be due to a large number of patients entering the next season with aggravated conditions and increased hypersensitivity caused by the high amount of pollen in the air.

Future Outlook

It would be expected that prevalence and severity will decrease when one considers the projected number of Japanese cedar trees that will be felled by the forestry industry and meteorological effects such as global warming, but it is believed that the airborne pollen levels will actually continue to rise. According to forecasts by Koji MURAYAMA, the amount of pollen in the air will increase to 170% (an estimate of 161% has recently emerged) of current levels by the year 2050 and the number of hay fever patients will increase by 140%.

There is also a theory that, due to its role as an important source of timber, the practice exists of planting large numbers of Japanese cedar trees without any regard for the ecosystem.

Onset Mechanism, Symptoms and Treatment of Japanese Cedar Pollinosis

The onset mechanism, symptoms and treatment of Japanese cedar pollinosis are the same as for other forms of hay fever, and there are not and particularly notable features particular to Japanese cedar pollinosis. For further details, refer to "Hay Fever."

Research into Japanese Cedar Pollinosis

Research has found that there is crossability between Japanese cedar pollen and Japanese cypress pollen.

Information within Japan

A system has been developed to make pollen dispersal information widely available for the many Japanese sufferers of the condition. This system is summarized below.

Definition of Pollen Dispersal

First day of pollen dispersal' is the first day on which the observed pollen count per square meter exceeds a value of 1, but low-level pollen dispersal begins actually before the first day of pollen dispersal.
Susceptible patients will exhibit symptoms before this time but there are also investigations that have found that the majority of patients will display symptoms before this time, and this has led to doubts regarding the significance of the 'first day of pollen dispersal.'

Airborne Pollen Level

The first systematic Japanese cedar pollen investigation was begun in 1965 by the current National Hospital Organization Sagamihara National Hospital. Analysis of the data from this hospital shows that the current airborne pollen level is 200-300% higher than the time at which the study was started. Airborne pollen levels in 1982 when Japanese cedar pollen allergy became recognized as a social problem were approximately 400% of 1965 levels. It is clear that increases in airborne pollen levels and the number of individuals exposed to this pollen are the main reasons for the increase in the number of patients developing symptoms (this is supported by the above correlation with symptom prevalence rate by area).

The reason for the increase in airborne pollen levels is the widespread Japanese cedar afforestation that took place throughout Japan after the Second World War in order to provide building materials as well as for the purposes of flood control and forest conservation, and it was in the latter half of the 1960s that these trees began to reach the age of 30 years when they have the greatest pollen producing capacity. The area of such Japanese cedar forests consisting of trees producing large amounts of pollen continues to increase (refer to "Social Aspects").

In recent years it has also been identified that the pollen dispersal period is increasing in length. This is thought to be caused by the blooming of Japanese cedar trees in high altitude areas, which were planted slightly later and developed more slowly, later than the blooming of trees located in flat areas. It has also been identified that global warming is causing the pollen dispersal season to occur earlier.

The amount of flowers developed by Japanese cedar trees is influenced by summer climate. However, this is not the only factor and just as fruit trees have a main season crop and an off-season crop, patterns have also been observed in which airborne pollen levels fluctuate every other year or on a 2-3 year basis. But there are also situations in which this is not the case such as the continued four year high pollen levels in the Kanto region from 2000 to 2003. In recent years, particularly high airborne pollen levels were recorded in 1995 and 2005.

Pollen Forecast

The Japan Weather Association began the first Japanese cedar pollen information service for the general public on March 9, 1987. The service came to provide daily airborne pollen level forecasts for central Tokyo and the Tama area based on forecasts that have been made by the Tokyo Metropolitan Government Bureau of Public Health since 1985. Other cities including Kyoto and Sendai also began providing such information as a civic service in the same year. Daily airborne pollen forecasts by area are now available in newspapers, on television (weather forecasts), via the internet (including mobile telephones and E-mail) and by telephone.

Forecasts are made based on factors including the appearance of Japanese cedar buds in the year proceeding the season (Japanese cedar pollinosis season). The effects of climate (weather) also influence pollen levels and the time when pollen dispersal begins.

Airborne pollen levels are forecast as high or low in comparison to an average year, but average year values consist of an average of levels from the previous 10 years and, as average values continue to rise, it is necessary to exercise caution when interpreting forecast values. For example, in 2006 it was forecast that 'airborne pollen levels will be 60% of an average year' but this was essentially equal to the average value reported 10 years before. Taking Tokyo as an example, the average year value in 2006 was essentially equal to the previously mentioned four year period from 2000 to 2003. Therefore even if a forecast predicts levels lower than those of an average year, this does not necessarily mean that levels will be low.

A forecast of 'low' according to a system that states 'values for this year will be high/low' would serve to make many patients feel at ease and less likely to take preventative steps. Moreover, a forecast of 'levels for this season will be low' does not guarantee that airborne pollen levels will be low every day, so it is important to be cautious.

Administrative Countermeasures

There is continued active discussion and implementation of countermeasures in Japan due to the fact that Japanese cedar pollinosis affects such a large number of Japanese people. Examples of these are given below.


The Japanese government held the 'Japanese Cedar Pollinosis Liaison Conference for Concerned Government Agencies' in 1990 and since 1994 the Science and Technology Agency has conducted 'integrated research to overcome cedar pollinosis' over several years. The name of the conference was changed to the 'Pollinosis Liaison Conference for Concerned Government Agencies' in 2004 and since 2005 concrete initiatives have been implemented based on fundamental research.

Such administrative actions include the Liberal Democratic Party 'Federation of Diet Members for Measures Against Pollinosis and Other Allergies' (commonly known as Hakushon Giren, secretary general: lower house member Shinya ONO) which was established by Shinzo ABE and approximately 50 (at the time) other Diet members in 1995, and has had a major impact on the national implementation of serious efforts. As a result, the budget allocated for countermeasures against allergies including pollinosis has increased drastically, and the allergy related budget for 2002 reached 7.372 billion yen, which was 27 times more than that of the seven years before. Measures such as the permission to use the 'allergy clinic' medical specialty in 1996 and the founding of the RIKEN Research Center for Allergy and Immunology in 2003 were also due to the actions of Diet members.

However in recent years, the Ministry of Health, Labor and Welfare held an open symposium to encourage all government agencies to work together with regard to countermeasures such as bulletins prior to the 2005 Japanese cedar pollinosis season in which unprecedentedly high airborne pollen levels were forecast but it was unable to finalize any unified national policies or meet public expectations, and the season passed without any visible initiatives.

The majority of the pollinosis countermeasures implemented by the administration consist of fundamental research, the development of treatments and the improvement of airborne pollen forecasting technology, and there is increasing criticism that fundamental countermeasures against the sources of Japanese cedar and Japanese cypress pollinosis are being neglected. Diet discussions take place but lead only to repeated ad hoc piecemeal measures with no major progress made (there are those who consider the fundamental reasons of this to be the small budget allocated to the Forestry Agency and neglect of the nation's primary industry).

Despite multiple results indicating no relationship, the Ministry of the Environment continues to investigate the relationship between air pollution and such allergies. The administration is also ridiculed for not terminating research due to an unwillingness to acknowledge responsibility for past misgovernment (although it is certain that air pollution does pose various health problems. A new procedure based on the knowledge of recent years is required). A new procedure based on the knowledge of recent years is required).

Transplantation and Deforestation

In 2005, the Forestry Agency announced plans to plant 600,000 pollen-free cedar trees during the next five years but when it is considered that 1 hectare contains 3,000 trees, this is equivalent to a total of only 200 hectares (Japanese cedar tree forests occupy approximately 4,530,000 hectares in Japan).

On the other hand, the Forestry Agency focused its pollinosis countermeasures on the selective felling Japanese cedar trees but in 2006 the media brought to light an announcement that caused misunderstanding regarding the suppressive effect on pollen, and there is doubt surrounding the passive stance toward conventional transplantation.

In response to these criticisms, the Forestry Agency launched countermeasures to combat the sources of pollen in 2008. The project aims to halve the sources of pollen carried to the Tokyo area and the Kyoto-Osaka region within 10 years. However, its effectiveness is unclear as maintenance of the seedling supply system is ongoing (the plan is to increase the supply of low-pollen Japanese cedar seedlings to approximately 11 million by the year 2017) and forest owners find it difficult to consider felling or transplantation due to the low price of cedar wood.

National, prefectural and incorporated administrative agency research institutions had developed 121low-pollen Japanese cedar cultivars and 1 pollen-free Japanese cedar cultivar as of 2008.

Simulation Technology
Improvements in real-time data observations and simulation technology have been utilized not only in pollen dispersion forecasts but also in the identification of pollen sources. These have made it possible to implement forestry countermeasures and effective initiatives in locations that produce large quantities of pollen and in which there is a great effect on densely-populated areas. The fact that such countermeasures are funded by taxpayer's money means that wastage must be avoided, and these initiatives therefore receive more attention than they once did. Research was also conducted.

In May 2006, The Forestry Agency declared that it would produce a map of pollen sources and implement measures such as transplantation with priority to those areas that are most greatly affected. Following this, the Forestry Agency formed the 'Pollen Source Countermeasure Project Team' and produced a report in April 2008. The findings of this report were reflected by the previously mentioned Pollen Source Countermeasure Project.

Functional Foods

The National Institute of Agrobiological Sciences has developed a rice cultivar for the treatment of Japanese cedar pollinosis which contains the Japanese cedar pollen antigen but the Ministry of Health, Labor and Welfare does not recognize this as a food product. The National Institute of Vegetable and Tea Science has developed the Benifuki tea variety, and the methylated catechins that it contains are reported to suppress pollinosis. However, the demonstration of the effects and efficacy of foods are regulated by the Pharmaceutical Affairs Act and some point out that it is not appropriatefor the de facto national institutions to state the effects and efficacy of such products. On the other hand, major companies that actually manufacture and market Benifuki tea products have not demonstrated effectiveness or efficacy against pollinosis. In addition, some people say that it was also the Hakushon Giren that requested the commercialization of such products. These factors have led to criticism that government measures disregard patients, and there are also those who claim that actions of the divided government are resulting in adverse effects.

Insurance Policies

Regarding the desensitization therapy - the only effective fundamental therapy (refer to "Treatment"), the health service also hasn't taken any action although its low assessment by the insurance industry has been identified as a factor inhibiting the widespread use of this therapy. It is claimed that attempts are being made to publicize care and treatment guidelines as much as possible but the fact remains that many inappropriate treatments continue to be carried out. New treatments (pharmaceuticals) that will likely be put to practical use in future require significant expense, and there is concern about whether or not these will be recognized by the insurance industry.

Tokyo Initiatives

In Tokyo, which has independently implemented research and measures into pollinosis and allergies including the Pollen Allergy Measurements and Review Committee implemented in the latter half of the 1980s and the Allergic Disease Countermeasures Investigation Committee founded in 1998, countermeasures against forests which are a source of pollen have been compiled and these were put into operation in 2006. The administration was ridiculed for hurriedly implementing measures because Tokyo Governor Shintaro ISHIHARA suffered from Japanese cedar pollinosis during the 2005 pollen season, but this was a fact.
At a governor's press conference on March 10, 2006, Ishihara acknowledged this by stating as follows:
I had never suffered from hay fever before but on developing it last year, I suddenly became aware of the issue.
That is the way human beings are.'

The project, which is named 'Kafun no Sukunai Morizukuri' (lit. The Creation of Low-Pollen Forests) and has conservationist and author C. W. NICOL serving as representative promoter, aims to fell Japanese cedar forests in the Tama area and transplant them with low-pollen Japanese cedar cultivars and broadleaf trees over a 50 year period as well as reduce pollen levels by 20% over the next 10 years. However, there is a budget deficit and fundraising activities are being conducted. The plan also promotes the consumption of timber from the Tama area. The project does not simply consist of promoting felling and transplantation, and the agreement of a concrete target value of reducing pollen levels by 20% was groundbreaking. The nonpartisan Tokyo Assembly Federation for the Promotion of Pollinosis Countermeasures (chairman: Toshiaki KOGA) was also formed within the Tokyo Assembly.

The example set by Tokyo has spurred on the implementation of pollinosis countermeasures by cooperation between Tokyo, Kanagawa Prefecture, Chiba Prefecture, Saitama Prefecture, Yokohama City, Kawasaki City, Chiba City and Saitama City. There are demands that the national government also implement such policies. In a survey conducted in the above four prefectures and four cities, 56.4% of citizens responded that the pollinosis countermeasure that they most wanted the administration to implement was the felling and pruning of Japanese cedar trees.

However, it must be said that Tokyo is an autonomous body that enforced diesel regulation based on the concept that exhaust fumes from diesel vehicles was the cause for increases in pollinosis despite epidemiological investigation findings that there is no relationship between exhaust gas pollution and pollinosis (although these regulations did not pertain only to pollinosis). Prior to the start of the 2005 season, the governor stated the symptoms suffered by citizens this season should be milder because regulations had been implemented but the fact that this governor developed pollinosis in that very season remains a great irony in the history of pollinosis in Japan.

Experiments in which Tokyo treated Japanese cedar trees with maleic hydrazide in order to inhibit flower development were discontinued due to effects on the quality of the timber.

Areas Unaffected by Pollen

In 2005 the Hokkaido town of Kamishihoro-cho under the jurisdiction of the Tokachi subprefectural claimed to be area unaffected by pollen and in 2006 the Amami Islands in Kagoshima Prefecture began to attract tourists (pollinosis patients) for the purpose of recuperation with the Ministry of Land, Infrastructure, Transport and Tourism taking applications and operating the trips on a trial basis. The movement of autonomous bodies into such hay fever businesses is particularly noteworthy.

Japanese Cypress Pollen and Hay Fever

As is the case with Japanese cedar trees, Japanese cypress trees which were widely planted around 10 years later than Japanese cedar trees are also gradually reaching an age at which they have a high pollen producing capacity. Despite the fact that the anthesis of Japanese cypress trees is later than for Japanese cedar trees, they produce slightly more pollen which prolongs the duration for which patients exhibit symptoms.
(As stated previously, the majority of Japanese cedar pollinosis patients also react to Japanese cypress pollen.)

It is said that many Japanese cypress trees were planted in the west of the Kanto region (central area to the Kansai region) but it has been identified that a large number of a different type of Japanese cedar tree were also planted in this area. It is said that this is not an early season cultivar that disperses pollen from around the age of 30 years but a late season cultivar that disperses pollen from around age 50 years and, if this is true, then there is a concern that pollen from not only Japanese cypress trees but also from Japanese cedar trees will increase in the west of the Kanto region. Moreover, the amount of pollen produced varies greatly depening on the cultivar. For example, it is known that the Japanese cedar trees on Kyushu produce little pollen (refer to the above prevalence rates by prefecture).