Pathogenesis of solar urticaria. Sweat droplet in testing for photosensitivity.

It was impossible to replicate solar urticaria lesions by irradiation in the laboratory, until the role of sweating was recognized. We found that the sweat droplet, acting as a lens, serves as a photointensifier. As such, sweat would appear to play a meaningful role in the pathogenesis of cutaneous photosensitivity reactions, as well as be an adjuvant in phototesting.