Electron spectroscopic analysis of the human lipid skin barrier: cold atmospheric plasma-induced changes in lipid composition Marcel Marschewski 1 , Joanna Hirschberg 2 , Tarek Omairi 2 , Oliver Ho ¨ fft 3 , Wolfgang Vio ¨l 2,4 , Steffen Emmert 5 * and Wolfgang Maus-Friedrichs 1,6 * 1 Institute of Energy Research and Physical Technology, Clausthal University of Technology, Clausthal-Zellerfeld, Germany; 2 Faculty of Natural Sciences and Technology, University of Applied Sciences and Arts Hildesheim/Holzminden/Go ¨ttingen, Go ¨ttingen, Germany; 3 Clausthaler Zentrum fu ¨r Materialtechnik, Technische Universita ¨t Clausthal, Clausthal-Zellerfeld, Germany; 4 Fraunhofer Institute for Surface Engineering and Thin Films IST Application Center for Plasma and Photonic APP, Go ¨ttingen, Germany; 5 Department of Dermatology, Venerology, and Allergology, University Medical Center Go ¨ttingen, Go ¨ttingen, Germany; 6 Institute of Particle Technology, Clausthal University of Technology, Clausthal-Zellerfeld, Germany Correspondence: Prof. Dr. Wolfgang Maus-Friedrichs, Technische Universita ¨t Clausthal, Institut fu ¨r Energieforschung und Physikalische Technologien, Leibnizstr. 4, 38678 Clausthal-Zellerfeld, Germany, Tel.: +49 5323/72-2310, Fax: +49 5323/72-3600, e-mail: w.maus-friedrichs@pe.tu-clausthal.de *Joint senior authorship. Abstract: The lipids of the stratum corneum comprise the most important components of the skin barrier. In patients with ichthyoses or atopic dermatitis, the composition of the skin barrier lipids is disturbed resulting in dry, scaly, itching erythematous skin. Using the latest X-Ray Photoelectron Spectroscopy (XPS) technology, we investigated the physiological skin lipid composition of human skin and the effects of cold atmospheric plasma treatment on the lipid composition. Skin lipids were stripped off forearms of six healthy volunteers using the cyanoacrylate glue technique, plasma treated or not and then subjected to detailed XPS analysis. We found that the human lipid skin barrier consisted of 84.4% carbon (+1.3 SEM%), 10.8% oxygen (+1.0 SEM%) and 4.8% nitrogen (+0.3 SEM%). The composition of physiological skin lipids was not different in males and females. Plasma treatment resulted in significant changes in skin barrier lipid stoichiometry. The total carbon amount was reduced to 76.7%, and the oxygen amount increased to 16.5%. There was also a slight increase in nitrogen to 6.8%. These changes could be attributed to reduced C-C bonds and increased C-O, C=O, C-N and N-C-O bonds. The moderate increase in nitrogen was caused by an increase in C-N and N-C-O bonds. Our results show for the first time that plasma treatment leads to considerable changes in the human skin lipid barrier. Our proof of principle investigations established the technical means to analyse, if plasma-induced skin lipid barrier changes may be beneficial in the treatment of ichthyotic or eczematous skin. Key words: cold atmospheric plasma – epidermal barrier – skin lipids – X-Ray Photoelectron Spectroscopy Accepted for publication 1 October 2012 Introduction The lipids of the stratum corneum comprise the main compo- nents of the hydrophobic human skin barrier regulating water homoeostasis (1,2). The epidermal lipid barrier film is composed of a more or less equimolar mixture of ceramides, cholesterol and long-chain free fatty acids. Seven different ceramides belong- ing to the class of sphingolipids can be discerned (2) and espe- cially the ceramide profile may be important in relation to the barrier function of the skin. In general, there is quite limited data on the physiological lipid profile of human skin (3), for example, in relation to age or gender. Increased age may lead to an overall reduced lipid content in human skin (4,5). Jungersted et al. (1) found that a higher ceramide/cholesterol ratio was present in men compared with women. Reduced amounts of ceramide 3 were found to be associated with increased transepidermal water loss, a marker for a disturbed skin barrier function (6,7). More recently, the notion that mutations in the filaggrin gene result in autosomal-dominant ichthyosis vulgaris (8) and are associated with atopic eczema (9) – both diseases with severe defects in skin barrier function – has fostered interest in research of normal human skin lipid barrier and changes of skin lipids in diseased skin. For example, patients with atopic eczema and common filaggrin mutations exhibited different amounts of the ceramides 1, 4 and 7 compared with healthy controls. Interestingly, these patients also exhibited higher skin pH values and a higher ery- thema rate (10). In cold plasma medicine, a new field, anti-inflammatory, anti- itch, anti-microbic, UV and other therapeutic modalities are com- bined within one plasma (ionized air) treatment (11–15). Published cold plasma applications include successful treatment of atopic eczema as well as other pruritic diseases (12,13,16). Gen- erally, two types of cold plasma can be discerned: direct plasma (dielectric barrier discharge – DBD, corona discharge) and indirect plasma (plasma torch, plasma jet). While dielectric barrier dis- charge (DBD), plasma treatment of technical surfaces is a standard method since years, the DBD plasma treatment of biological tissue is quite novel (17,18). DBD generates a low-temperature plasma under atmospheric pressure and, thus, is a suitable instrument for a non-destructive treatment of biological material (19). For our investigation, a non-equilibrium, weakly ionized physical DBD plasma is generated by the application of high voltages across small gaps, whereas the electrode is covered by a dielectric. This ª 2012 John Wiley & Sons A/S Experimental Dermatology, 2012, 21, 921–925 921 DOI: 10.1111/exd.12043 www.blackwellpublishing.com/EXD Original Article