Contact allergy due to lichens in patients with a history of photosensitivity.

Ten patients with a history of photosensitivity and of a rash showed abnormal reactions to long-wave UVR. The rash occurred particularly in areas exposed to light, though other areas were occasionally involved. The development of the rash could in all patients be related to contact with lichens and although exposure to sunlight usually led to an aggravation of symptoms, some patients, particularly forestry workers, showed exacerbations even during the winter. Positive responses were observed in both irradiated and non-irradiated patch tests with different species of lichen and in several patients irradiation precipitated a stronger response. These findings suggest that lichens can cause both contact and photocontact dermatitis. The suspected allergens contained in these lichens are atranorin, physodalic and pysodic acids.