BACKGROUND: It is disputed whether increases in self-reported respiratory allergy represent a true increase or merely increased recognition. We aimed to investigate whether the prevalence of skin-prick-test (SPT)-positive allergic rhinitis had increased in an adult general population in Copenhagen, Denmark.

METHODS: Two cross-sectional surveys were carried out in 1990 and 1998. A screening questionnaire on respiratory symptoms in random samples of 15-41-year-olds preceded both surveys. Among the responders, random samples were invited to a health examination including SPT. Totals of 312 (participation rate 74.6%) and 482 (participation rate 53.4%) subjects were examined in 1990 and 1998, respectively. Diagnoses of SPT-positive allergic rhinitis were based on a history of nasal symptoms on exposure to allergens and SPT positivity to allergens.

RESULTS: The prevalence of a diagnosis of SPT-positive allergic rhinitis increased from 12.9% to 22.5% (adjusted odds ratio 1.94, 95% CI 1.30-2.90), whereas the prevalence of a positive SPT (allergen histamine wheal ratio > or = 0.5) to one or more of 10 allergens increased from 27.7% to 33.9% (adjusted odds ratio 1.47, 95% CI 1.05-2.05).

CONCLUSIONS: The prevalence of SPT-positive allergic rhinitis has increased significantly. Our findings indicate that a true increase in respiratory allergy has occurred.