SKIN PIGMENTATION CHARACTERIZED BY VISIBLE REFLECTANCE MEASUREMENTS

The epidermal melanin content affects most dermatologic treatments inv olving light, and can limit the therapeutic success significantly. The refore, knowledge of the optical properties of skin is required. This study investigates how the concentration of melanin influences visible reflectance spectra of skin and the relationship to threshold radiant energy fluence for melanosomal or melanocyte destruction, Reflectance spectra were measured at 28 pigmented human skin sites in vivo. For A sian and Caucasian subjects, measured reflectance values varied over t he same range, while significantly lower values were recorded for Afri can individuals. Epidermal melanin absorption coefficients measured at 694 nm were about 2500 m-l for African, and 300-1200 m(-1) for Caucas ian and Asian skin. Twenty-five skin sites were exposed to ruby laser pulses (694 nm), where the pulse duration was long enough to allow hea t diffusion between melanosomes. Hypopigmentation occurred, on average , at 12 and 26 J cm(-2) for sun-exposed and sun-protected white skin, respectively, while slightly lower threshold values resulted from the measured spectra. As visible reflectance spectra reveal information re garding skin pigmentation and individual threshold doses for melanosom al damage, a use as a diagnostic tool in various dermatological laser treatments is apparent.