Department of Dermatology, University of Kiel, Kiel, Germany.
J Dermatol. 2018 Sep;45(9):1044-1052. doi: 10.1111/1346-8138.14489. Epub 2018 Jun 4.
The pH plays an important physiological role in nature and humans. pH varies from 1 to 8 in human organs with tight regulation in blood and epithelia of barrier organs. The physiological pH of the stratum corneum is 4.1-5.8 and several mechanisms contribute to its formation: filaggrin degradation, fatty acid content, sodium-hydrogen exchanger (NHE1) activation and melanosome release. First, the acidic pH of the stratum corneum was considered to present an antimicrobial barrier preventing colonization (e.g. by Staphylococcus aureus and Malassezia). Later on, it was found that the pH influences skin barrier function, lipid synthesis and aggregation, epidermal differentiation and desquamation. Enzymes of ceramide metabolism (e.g. β-glucocerebrosidase or acid sphingomyelinase) as well as proteases (e.g. chymotryptic enzyme or cathepsin D linked to epidermal differentiation and desquamation) are regulated by the pH. Experimental disruption of the physical barrier leads to an increase of pH, returning to normal levels only after many hours. Inflammatory skin diseases and diseases with an involvement of the epidermis exhibit a disturbed skin barrier and an increased pH. This is known for atopic dermatitis, irritant contact dermatitis, ichthyosis, rosacea and acne, but also for aged and dry skin. Normalizing the pH by acidification through topical treatment helps to establish a physiological microbiota, to repair skin barrier, to induce epidermal differentiation and to reduce inflammation.
pH 值在自然界和人类中起着重要的生理作用。人类器官的 pH 值在 1 到 8 之间变化,血液和屏障器官的上皮细胞有严格的调节。角质层的生理 pH 值为 4.1-5.8,有几种机制有助于其形成:角蛋白丝降解、脂肪酸含量、钠-氢交换器 (NHE1) 激活和黑色素体释放。首先,角质层的酸性 pH 值被认为是一种抗菌屏障,可防止定植(例如金黄色葡萄球菌和马拉色菌)。后来发现,pH 值影响皮肤屏障功能、脂质合成和聚集、表皮分化和脱屑。神经酰胺代谢酶(如β-葡糖脑苷脂酶或酸性鞘磷脂酶)以及蛋白酶(如与表皮分化和脱屑相关的糜蛋白酶或组织蛋白酶 D)受 pH 值调节。物理屏障的实验性破坏会导致 pH 值升高,只有在数小时后才会恢复正常水平。炎症性皮肤病和涉及表皮的疾病表现出皮肤屏障受损和 pH 值升高。特应性皮炎、刺激性接触性皮炎、鱼鳞病、酒渣鼻和痤疮,以及老年和干燥皮肤均如此。通过局部治疗酸化来使 pH 值正常化有助于建立生理微生物群、修复皮肤屏障、诱导表皮分化和减少炎症。