Solar urticaria. The relationship of photoallergen and action spectrum.

We studied six cases of solar urticaria immunologically and photobiologically. Serum in five patients and plasma in one patient yielded an immediate reaction when injected into the patients' own skin after light irradiation. These photoallergens were gel filtrated, and the molecular weights were determined. The result was compared with the action spectrum obtained by a monochrometer. In three patients, with the action spectrum in short visible light ranges (400 to 500 nm), the molecular weight of the photoallergen was 25,000 to 45,000 daltons. In a patient with an action spectrum from ultraviolet-A to short visible light ranges (330 to 520 nm), there was another photoallergen molecular weight that was 300,000 to 1,000,000 daltons. In a patient with a wide action spectrum from ultraviolet-B to long visible light ranges (290 to 630 nm), photoallergens, which were believed to be multiple, were generated only from plasma.