The quantitative assessment of the skin barrier’s integrity in vivo holds significant potential across various clinical applications, encompassing diagnosis, ongoing monitoring, preventative measures, and the evaluation of therapeutic interventions. Both invasive and non-invasive techniques have been developed to investigate the functionality of the skin barrier. Among the non-invasive approaches, examples include the measurement of skin hydration, colorimetry, skin surface pH, and sebometry. However, these methods offer limited insights into diverse skin attributes and states, lacking a direct measurement of the skin barrier’s performance. A widely employed technique, known as trans-epidermal water loss (TEWL), is susceptible to the influence of various environmental factors. Its accuracy is dependent upon factors such as humidity, temperature, and the level of skin hydration. Electrical impedance spectroscopy (EIS) emerges as a promising non-invasive solution for assessing skin barrier function in vivo. By gauging the tissue’s electrical impedance across various frequencies, EIS furnishes insights into the structural integrity of the skin, thereby revealing its underlying pathophysiological condition. The distinctions in cell size, shape, orientation, compactness, intercellular fluid caused by inflammation and membrane structures between normal and pathological tissues are encapsulated within the impedance measurements. Noteworthy EIS applications encompass the identification of malignant tissues in melanoma, breast, prostate, and skin, as well as the characterization of tissue alterations subsequent to ischemia. A pivotal breakthrough by Rinaldi et al. spotlighted EIS as a means to probe epithelial barrier function in vivo. Our initial studies conducted on mice showcased EIS’s utility and reliability in pinpointing skin barrier impairments. Upon experimentally inducing skin barrier damage through procedures like tape stripping and the topical application of proteases (papain, trypsin, cholera toxin), an evident drop in skin electrical impedance was observed. This trend exhibited an inverse correlation with TEWL. Moving to a clinical milieu, EIS exhibited its prowess in quantifying the skin barrier’s status among patients with atopic dermatitis (AD). The tool demonstrated commendable specificity and sensitivity in distinguishing between healthy controls, non-lesional skin of AD patients, and the lesional skin of those afflicted with AD. EIS further facilitated the assessment of skin lesion recovery post-treatment, with strong correlations established between EIS measurements, disease scoring systems like SCORAD, pruritus scores, and even the tandem repeat count of FLG genes. The spectrum of potential clinical applications for EIS is broad. A notable proposition is its utilization in identifying infants at a heightened risk of developing AD through a swift, non-invasive assessment. This, in turn, could enable the recommendation of preemptive measures to fortify the skin barrier and mitigate exposure to environmental factors. In the context of AD, where a pressing need exists for novel monitoring tools to forecast exacerbations and gauge lesion response to therapy, EIS emerges as a valuable candidate. By bridging the gap between objective disease assessment and lesion monitoring, EIS holds significant promise in advancing dermatological care.
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