Polymorphous light eruption: eliciting and inhibiting wavelengths.

In 38 patients with polymorphous light eruption (PLE) photoprovocation tests were performed by applying 100 J/cm2 of UV-A to the extensor side of the upper arm on three consecutive days. Test sites were divided into four areas by covering the patients' skin with Schott glass filters WG 320, WG 335, WG 360, and GG 385 (or GG 395). In 17 patients typical skin lesions could be provoked in at least one test field. 10 patients reacted either at all test sites or at shorter wavelengths (simultaneously higher doses) only. In the remaining 7 patients test reactions did not occur underneath filters with lower cut-off points, whereas skin lesions were induced by radiation deprived of the shorter wavelengths passing through these filters. This observation suggests an inhibitory effect of shorter wavelengths in these cases.