Detection of action, inhibition and augmentation spectra in solar urticaria.

BACKGROUND: The action spectrum of solar urticaria varies among cases. In addition, light spectra outside the activating wavelengths can influence the wheal formation in selected patients.

OBJECTIVE: To know the mechanisms of light energy, we examined the effect of wavelengths on the skin and the serum factor.

METHODS: The patient's skin and serum were exposed to artificial light sources, in vivo and in vitro, respectively.

RESULTS: The action spectrum ranged from UVA to visible light (approximately 480 nm). The exposure to longer wavelengths immediately after the exposure inhibited the development of urticaria. Conversely, the irradiation of longer wavelengths before exposure increased the wheal formation. Furthermore, UVB irradiation prior to the exposure of urticaria-eliciting light also increased the urticarial reaction, while postirradiation of UVB had no effect. The patient developed an urticarial wheal at the site of injection of her own serum, which had been previously exposed to the action spectrum in vitro. Preirradiation increased the production of the photosensitizer, while postirradiation revealed no effect. Ultrafiltration techniques showed that the molecular weight of the photosensitizer is more than 300 kD.

CONCLUSION: We detected action, inhibition and augmentation spectra in a patient with a severe solar urticaria. Various wavelengths influence the wheal-forming factor in complex interactions.