In vivo Raman Microspectroscopy: Intra- and Intersubject Variability of Stratum Corneum Spectral Markers

In vivo Raman spectroscopy is a powerful tool for real-time analysis and in situ evaluation of tissues such as the skin. The efficiency of this technique has been widely demonstrated as a label-free method for in vivo evaluation of the skin. The aim of this study is to gather information about inter- and intra-individual variations in the spectral descriptors of water content and structure, organization of the lipid barrier and structure of proteins in the stratum corneum (SC).

In vivo SC measurements were performed on 17 female volunteers aged 20-30 years (phototypes I and II). For intra-individual variability, spectral collection was performed on 5 successive days per volunteer. Shapiro-Wilk and Cochran tests were applied to check the normality and the homoscedasticity of variances. ANOVA was then applied to evaluate intra- and intergroup variability.

ANOVA was performed on the spectral descriptors of water content and structure, organization of the lipid barrier and secondary structure of proteins in the SC. No significant intra- and interday variability was observed for all volunteers. Despite the low value of the total relative standard deviation, a highly significant variation was observed between volunteers.

Interindividual variability for Raman measurements is significant for a set of volunteers with normal nondiseased SC and close phototypes. This variability should be taken into consideration as a threshold for significant variance when working in vivo.