INM - Leibniz Institute for New Materials, 66123, Saarbrücken, Germany.
Department of Dermatology, Venereology and Allergology, Center of Experimental and Applied Cutaneous Physiology (CCP), Charité - Universitätsmedizin Berlin, Corporate Member of Freie Universität Berlin and Humboldt Universität zu Berlin, Charitéplatz 1, 10117, Berlin, Germany.
Exp Dermatol. 2023 Jul;32(7):986-995. doi: 10.1111/exd.14802. Epub 2023 Apr 4.
Glabrous skin is hair-free skin with a high density of sweat glands, which is found on the palms, and soles of mammalians, covered with a thick stratum corneum. Dry hands are often an occupational problem which deserves attention from dermatologists. Urea is found in the skin as a component of the natural moisturizing factor and of sweat. We report the discovery of dendrimer structures of crystalized urea in the stratum corneum of palmar glabrous skin using laser scanning microscopy. The chemical and structural nature of the urea crystallites was investigated in vivo by non-invasive techniques. The relation of crystallization to skin hydration was explored. We analysed the index finger, small finger and tenar palmar area of 18 study participants using non-invasive optical methods, such as laser scanning microscopy, Raman microspectroscopy and two-photon tomography. Skin hydration was measured using corneometry. Crystalline urea structures were found in the stratum corneum of about two-thirds of the participants. Participants with a higher density of crystallized urea structures exhibited a lower skin hydration. The chemical nature and the crystalline structure of the urea were confirmed by Raman microspectroscopy and by second harmonic generated signals in two-photon tomography. The presence of urea dendrimer crystals in the glabrous skin seems to reduce the water binding capacity leading to dry hands. These findings highlight a new direction in understanding the mechanisms leading to dry hands and open opportunities for the development of better moisturizers and hand disinfection products and for diagnostic of dry skin.
无毛皮肤是指无毛发且汗腺密度较高的皮肤，主要分布在哺乳动物的手掌和脚底，表面覆盖着厚厚的角质层。手部干燥常常是一种职业性问题，值得皮肤科医生关注。尿素是皮肤天然保湿因子和汗液的成分之一。我们使用激光扫描显微镜发现，手掌无毛皮肤的角质层中存在结晶尿素的树突状结构。我们利用非侵入性技术对活体尿素结晶的化学和结构性质进行了研究。并探讨了结晶与皮肤水合作用的关系。我们使用激光扫描显微镜、拉曼光谱和双光子断层扫描等非侵入性光学方法分析了 18 名研究参与者的食指、小指和大鱼际区域。使用皮肤电导率仪测量皮肤水合作用。约三分之二的参与者的角质层中存在结晶尿素结构。结晶尿素结构密度较高的参与者皮肤水合作用较低。拉曼光谱和双光子断层扫描中的二次谐波信号证实了尿素的化学性质和晶体结构。无毛发皮肤中存在尿素树突状晶体似乎降低了水结合能力，导致手部干燥。这些发现为理解导致手部干燥的机制提供了新的方向，并为开发更好的保湿剂和手部消毒剂以及诊断干燥皮肤提供了机会。
