Photosensitivity and allergy to aromatic lichen acids, Compositae oleoresins and other plant substances.

Sixteen patients with verified light sensitivity to both UVB and UVA wavebands showed allergic reactions to various lichen plants (Parmelia spp., Hypogymnia spp., Pseudovernia spp., Cladonia spp., Platismatia spp., Physcia spp., Umbilicaria spp. and Cetraria spp.). Among the aromatic lichen compounds, atranorin was observed to be the most frequently involved allergen, but also several other isolated lichen acids were immunologically active: d-usnic, evernic, stictic, fumarprotocetraric, lobaric, salazinic, diffractaic and physodic/physodalic acid. Several patients showed allergy to other plant substances from other sources such as seven different species from the Compositae family, alantolactone, balsam of Peru, colophony and wood tars. Sensitivity to known photosensitizers was observed in four patients. Aromatic lichen acids are UV-absorbing substances and several are evidently able to photosensitize human skin.