Influence of the pollen season on immediate skin test reactivity to common allergens.

We studied the reproducibility of skin prick test reactions and tested 65 young men, picked from a population survey, in spring and fall. We used 16 extracts from two manufacturers with 12 common allergens. The extracts employed on both occasions were from the same allergen batches and the testing procedure was the same. Four subjects who reacted negatively in spring turned positive when re-tested in fall; the opposite happened to one subject. The result remained positive or negative on both occasions in 92%. The best reproducibility (96%) was obtained by pollens. The reactivity against tree and grass pollens was higher in fall than in spring; this is obviously a result of the immunologic stimuli induced by exposure to pollens during the season. The reactions caused by animal danders and house dust were, however, smaller in fall than in spring. This is believed to be due to young people being less exposed to indoor dust in summer. The immediate skin test reactivity is influenced by several factors; we would like to add one: the time of year when the test is applied. The reproducibility of skin prick test results is quite satifactory when the problem is approached as presented here.