Investigation of skin by ultraviolet remittance spectroscopy.

Remittance spectroscopy in the ultraviolet spectral region was used to investigate human skin in vivo. Untreated healthy skin showed a minimum remittance at 280 nm wavelength, corresponding to the keratin absorption band. At shorter wavelengths the remittance mostly originated from light scattering in the stratum corneum and at longer wavelengths subcorneal structures had increasing influence. The spectral remittance reflected variations in pigmentation most sensitively in the UVA region. Hydration of the skin yielded a hypsochromic shift of the keratin absorption band due to changes in polarity and proton concentration in the environment of the chromophores. Remittance spectroscopy allows detection of topically applied drugs, whose penetration into the skin can be evaluated from the time-dependence of the remittance.