The spectral dependence for UVA-induced cumulative damage in human skin.

The wavelength dependence for UVA-induced cumulative damage was investigated in human skin. Epidermal changes (stratum corneum thickening, viable epidermal thickening sunburn cell production), as well as dermal alterations (lysozyme deposition, inflammation), were used as indices of cumulative photoperturbation. UVA wavelengths between 320 nm and 345 nm were more effective than longer wavelengths (360-400 nm) in inducing viable epidermal thickening. Similarly, the shorter wavelengths (320-345 nm) elicited more sunburn cells, although these differences did not reach statistical significance. All UVA bands were equally effective in inducing the dermal markers. At equal fluences, wavelengths > 400 nm produced no measurable cutaneous alterations. These findings suggest that (i) chronic epidermal and dermal damages have different spectral dependence and (ii) the action spectrum for dermal damage in the UVA is broad, extending up to 400 nm, and is different from the acute erythema spectrum in humans.