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Hay fever in Japan
is most commonly caused by pollen from ''Cryptomeria japonica'' (known as ''sugi'' in Japanese and often incorrectly translated as "cedar") and Japanese cypress (known as ''hinoki''), two native Japanese tree species.
==Cause==
Hay fever was relatively uncommon in Japan until the early 1960s. Shortly after World War II, reforestation policies resulted in large forests of cryptomeria and Japanese cypress trees, which were an important resource for the construction industry. As these trees matured, they started to produce large amounts of pollen. Peak production of pollen occurs in trees of 30 years and older.〔(MEDICAL CONSULTATION RATE OF ALLERGIC RHINITIS AND POLLINOSIS SURVEILLANCE IN AICHI, JAPAN )〕 As the Japanese economy developed in the 1970s and 1980s, cheaper imported building materials decreased the demand for cryptomeria and Japanese cypress materials. This resulted in increasing forest density and aging trees, further contributing to pollen production and thus, hay fever. In 1970, about 50% of cryptomeria were more than 10 years old, and just 25% were more than 20 years old. By 2000, almost 85% of cryptomeria were over 20 years old, and more than 60% of trees were over 30 years old. This cryptomeria aging trend has continued since then, and though cryptomeria forest acreage has hardly increased since 1980, pollen production has continued to increase.〔(Yahoo Japan hay fever column 5302 detailing history of postwar cryptomeria forests ) 〕 Furthermore, urbanization of land in Japan led to increasing coverage of soft soil and grass land by concrete and asphalt. Pollen settling on such hard surfaces can easily be swept up again by winds to recirculate and contribute to hay fever. As a result, approximately 25 million people (about 20% of the population) currently suffer from this type of seasonal hay fever in Japan.
In studies focused on atopic dermatitis (which can be caused or aggravated by hay fever or other allergies) it was found that exposure to microwave radiation from a cell phone can worsen existing allergies to house dust mite and cryptomeria pollen. In a randomized controlled trial, exposure to a cell phone that was actively transmitting increased allergen specific IgE production, whereas sham exposure did not.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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