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Chemical imaging of the stratum corneum under controlled humidity with the attenuated total reflection Fourier transform infrared spectroscopy method.

Attenuated total reflection Fourier transform infrared spectroscopic imaging was applied to study human stratum corneum (SC) tissue, the outermost layer of the skin. This imaging approach was combined with a controlled environment cell to demonstrate the possibility of obtaining chemical images of SC exposed to a wide range of relative humidities and diffusion of ethanol through the SC tissue with a specially designed liquid cell. The effect of water vapor sorbed into the SC on the distribution of other components in the SC was studied. Principal component analysis was applied in conjunction with univariate analysis to differentiate the distribution of different components in the SC. Swelling of the SC, a heterogeneous distribution of natural moisturizing factor and water, was detected upon the increase of relative humidity. The approach to image the penetration of liquid ethanol into the SC was also demonstrated and showed good potential and implications for studying transdermal drug delivery.