Effects of Aging on the Natural History of Seasonal Allergic Rhinitis in Middle-Aged Subjects in South Chiba, Japan

<i>Background:</i> The natural history of allergic rhinitis has been examined in a few longitudinal studies. The purpose of the study was to investigate the course, development and remission of seasonal allergic rhinitis (SAR) over 10 successive years in middle-aged subjects. <i>Methods:</i> An annual questionnaire survey on allergic rhinitis symptoms combined with an examination of specific IgE has been undertaken in a rural town in south Chiba since 1995. The analyzed subjects were 703 residents who underwent every examination in 1995, 2004 and 2005. In the last 15 years, the annual pollen count in Chiba was highest in 2005. <i>Results:</i> The sensitization rates to cedar pollen decreased with age in the same subject groups over 10 years, but the prevalence of SAR was higher in 2005 compared with 1995. Of the 52 subjects with SAR in 1995, the symptoms had disappeared in 10 subjects in 2005. Specific IgE had converted to negative or borderline in 4 of these patients, had decreased but was still positive in 4 and was increased or unchanged in 2. During the 10-year period, 22 subjects developed SAR, of whom 12 had increased specific IgE and 10 had similar or decreased specific IgE in 2005. <i>Conclusion:</i> SAR induced by cedar pollen takes a chronic course in the majority of middle-aged patients in south Chiba, Japan. The prevalence of SAR increased over 10 years due to a high level of pollen exposure. Changes in specific IgE were not directly associated with the development or remission of SAR.