The value of patch testing with plants "as is" in diagnosing plant sensitization

Background: The number of commercially available plant allergens/extracts is limited and therefore patch testing with fresh/dried plant material may be a necessary supplement in diagnosing plant allergy. Objectives: To evaluate the usefulness of patch testing with plants "as is" compared to patch testing with commercial and in-house produced plant test materials and to report on species eliciting positive patch test reactions. Patients/Materials/Methods: Consecutive eczema patients, who were patch tested between January 2019 and December 2023 and who had at least one positive reaction to a plant allergen and/or extract and/or plant "as is" were included in the study. Results: A total 57 out of 1893 patients tested (3%) were sensitised to plants. Compositae plants were the most frequent sensitizers, followed by tomato, tulipalin A, falcarinol, and Philodendron plants. In 12 patients (21%), the diagnosis was based on patch testing with fresh plants only. Occupational sensitization occurred in 32%. Other sensitizers included Hydrangea, Pelargonium zonale, and Monstera. Conclusions: A large minority of plant-sensitised patients would have been undiagnosed without patch testing with plants "as is." Most of the culprit plants were known sensitizers, but not commercially available, and these and new species taken into cultivation makes patch testing with fresh plants unavoidable and worthwhile.