Thomas Leo Ogren

Thomas Leo Ogren is a horticulturist, allergy researcher, and author known for developing the Ogren Plant Allergy Scale (OPALS), a plant-allergy ranking system used by the U.S. Department of Agriculture. He holds a master's degree in agricultural science and has worked as a landscape gardening instructor, nursery owner, and gardening radio host. He lives in San Luis Obispo, California.