Erythema and melanogenesis action spectra in heavily pigmented individuals as compared to fair-skinned Caucasians

The protective role of epidermal melanin pigmentation against chronic exposure to ultraviolet radiation is widely accepted, although its photoprotective effect against acute exposure is less certain. In this study, the action spectra of erythema and melanogenesis in heavily pigmented individuals (skin type V) were determined at 295, 305, 315, and 365 nm, and compared with those of skin types I and II. When the erythema and melanogenesis action spectra for skin type V were normalized to 295 nm, they were identical to the corresponding action spectra for fair-skinned individuals, indicating that the photoprotection of epidermal melanin pigmentation is essentially independent of wavelength. The ratio of values for the minimum erythema dose (MED) between skin type V and skin types I and II was 2.29, which is close to the ratio of pigment in these skin types, as measured by diffuse reflectance spectroscopy in the visible range. The minimum immediate pigment darkening dose (IPD) and the minimum melanogenic dose (MMD) at 365 nm, and the MED and MMD at 315 nm were the same for all skin types, while the variation of MED for every skin type was maximum at 305 and 365 nm. The results provide circumstantial evidence that erythema and melanogenesis have the same mechanism at short-wavelength WE (295 and 305 nm), and different mechanisms in UVA (365 nm). Furthermore, the 24 h MED at 305 nm appears to be a sensitive indicator of skin type.