Solar urticaria induced by UVA and inhibited by visible light

An 18-year-old woman developed urticaria approximately 10 minutes after exposure to sunlight. The action spectrum was in the UVA range. Simultaneous irradiation of the skin with UVA and visible light wavelengths shorter than 460 nm induced wheals approximately 10 minutes after the end of the exposure, no matter how long the exposure time. Urticaria induced by UVA radiation was completely inhibited by immediate reirradiation of test sites with visible light wavelengths shorter than 460 nm. Visible light irradiation before exposure to eliciting wavelengths revealed no inhibitory effect, nor was an inhibitory effect found by pre- or postirradiation of test sites with visible light wavelengths longer than 530 nm. These findings suggest that the inactivation of a photoproduct or some subsequent step involved in the pathogenesis of the urticarial reaction was inhibited by visible light wavelengths shorter than 460 nm but not by visible light wavelengths longer than 530 nm.