THE SPECTRAL DEPENDENCE FOR UVA-INDUCED CUMULATIVE DAMAGE IN HUMAN SKIN

The wavelength dependence for UVA-induced cumulative damage was invest igated in human skin. Epidermal changes (stratum corneum thickening, v iable 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 3 45 nm were more effective than longer wavelengths (360-400 nm) in indu cing viable epidermal thickening, Similarly, the shorter wavelengths ( 320-345 nm) elicited more sunburn cells, although these differences di d not reach statistical significance, All UVA bands were equally effec tive in inducing the dermal markers. At equal fluences, wavelengths > 400 nm produced no measurable cutaneous alterations, These findings su ggest that (i) chronic epidermal and dermal damages have different spe ctral 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.