Allergy epidemiology in the St. Louis, Missouri, area. III. Trees.

A population skin-tested with pollen from twelve wind pollinated tree species showed a variable level of allergenicity, particularly among adults. Pollen extracts of Box Elder, Willow and Hickory elicited the highest allergic reactions, Oak, Birch, Sycamore, Black Walnut and Poplar more moderate reactions, while allergens from Cottonwood, Maple, Elm and White Ash were less reactive. Since Box Elder is ubiquitous and produces a strongly positive reaction among adults, it should be included among skin tests of those patients known to be allergic to early spring pollen.