After becoming interested in allergies as a botany student, Thomas Leo Ogren began to research the relationship between city planning and allergies. He found that most cities plant male trees and shrubs because they do not produce seeds that have to be swept up and removed. The pollen that male plants do produce, however, is the principal cause of allergies in people. Thomas Leo Ogren now works to encourage the planting of “messy” females in proportion to males to create allergy-free cities and gardens.
Thomas Leo Ogren is the creator of the Ogren Plant Allergy Scale (OPALS™), the first system for ranking the allergy-causing potential of plants.

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