Photosensitive psoriasis provoked by a suberythematous dose of ultraviolet-B light

An unusual case of 'photosensitive psoriasis' is reported. This patient had experienced an exacerbation after sea-bathing, and psoriatic eruptions were observed on the sun-exposed areas of the body. Phototesting with ultraviolet-B (UV-B) revealed his minimal erythema dose to be within normal limits. Three to four weeks after phototesting, however, he developed a psoriatic macule on the area exposed to the suberythematous dose of UV-B. The histologic features of the skin lesion provoked by UV-B irradiation were similar to those of naturally occurring lesions on areas covered by clothes. Moreover, failure to reproduce skin lesions following tape-stripping ruled out a proneness of this patient to develop the Köbner phenomenon nonspecifically.