Supplementary Material for: Sensitive Skin: Assessment of the Skin Barrier Using Confocal Raman Microspectroscopy

<p><b><i>Background/Aims:</i></b> Sensitive skin (SS), a frequently reported condition in the Western world, has been suggested to be underlined by an impaired skin barrier. The aim of this study was to investigate the skin barrier molecular composition in SS subjects using confocal Raman microspectroscopy (CRS), and to compare it with that of non-SS (NSS) individuals as well as atopic dermatitis (AD) and allergic rhinoconjunctivitis (AR) subjects, who frequently report SS. <b><i>Methods:</i></b> Subjects with SS (<i>n</i> = 29), NSS (<i>n</i> = 30), AD (<i>n</i> = 11), and AR (<i>n</i> = 27) were included. Stratum corneum (SC) thickness, water, ceramides/fatty acids, and natural moisturizing factor (NMF) were measured by CRS along with transepidermal water loss and capacitance on the ventral forearm, thenar, and cheek. Sebum levels were additionally measured on the forearm and cheek. <b><i>Results:</i></b> No differences between SS and NSS subjects were found regarding SC thickness, water, and NMF content, yet a trend towards lower ceramides/fatty acids was observed in the cheek. Compared to AD subjects, the SS group showed higher ceramides/fatty acid content in the forearm, whereas no differences emerged with AR. The correlation of macroscopic biophysical techniques and CRS was weak,<b> </b>yet<b> </b>CRS confirmed the well-known lower content of NMF and water, and thinner SC in subjects with filaggrin mutations. <b><i>Conclusion:</i></b> The skin barrier in SS is not impaired in terms of SC thickness, water, NMF, and ceramides/fatty acid content. The failure of biophysical techniques to follow alterations in the molecular composition of the skin barrier revealed by CRS emphasizes a strong need in sensitive and specific tools for in vivo skin barrier analysis.</p>