Action spectrum on UVA irradiation for formation of persistent pigmentation in normal Japanese individuals

Abstract

The minimum exposure required to produce persistent pigmentation (PP) on the skin of normal Japanese subjects was evaluated by means of monochromatic irradiation on the back using a high-intensity monochromator. PP was induced within the range of wavelengths up to 468 nm, with a peak from 330 to 370 nm, but it was not observed at 482 or 497 nm. When the PP production curve was obtained taking the spectral distribution of sunlight into account, it showed a peak at 340 nm centering in the UVA region and extending into the region up to 396 nm. Thus, it appears that solar UVA participates in PP formation.