Production and inhibition of solar urticaria by visible light exposure.

The mechanisms of production and inhibition of solar urticaria were investigated in two patients whose eruptions were induced by wavelengths ranging from approximately 400 to 500 nm. They developed urticarial reactions to their own sera, which had been exposed previously to light in vitro. The exposure of skin to light from which activating wavelengths were eliminated with a glass filter (O-55), immediately after the exposure to urticaria-eliciting light, significantly inhibited the development of urticaria. The irradiation with the filtered light prior to the exposure of urticaria-eliciting light revealed no inhibitory effect. The simultaneous exposure of action and inhibition spectra seemed to suppress urticaria formation. The exposure of the inhibition spectrum did not affect wheal formation produced by histamine and a histamine-releasing agent. The photosensitizer produced by the action spectrum may be inactivated by the inhibition spectrum, or the interaction between photosensitizer and antibody may be blocked by the irradiation with the inhibition spectrum.