Читать книгу pH of the Skin: Issues and Challenges - Группа авторов - Страница 40

The acidic nature of the skin surface was recognised more than a century ago and has been measured since 1928. Several non-invasive methods for measuring skin surface pH have been developed ever since and have contributed to our understanding of healthy and diseased skin. This chapter summarises the endogenous physiological, exogenous and environmental factors that influence skin surface pH and its measurement as well as the different measurement methods for skin surface pH, with specific emphasis on the classic planar glass electrode method. Also, practical guidance for measurement of skin surface pH using the planar glass electrode method is provided. Adherence to practical skin surface pH measurement (method) guidelines with due consideration and practicable control of all factors that may affect skin surface pH will ensure credible pH measurement results in our continuous pursuit of understanding especially diseased skin.

© 2018 S. Karger AG, Basel

Although the acidic nature of the skin surface was recognised more than a century ago, the first significant study on skin surface pH was carried out in 1928 [1, 2]. With crude technology, Schade and Marchionini reported a skin surface pH between 3 and 5. It is now, 90 years since the concept of an “acid mantle” of the skin was introduced by Marchionini. The skin surface pH is normally acidic and ranges between 4.2 and 6.1 [3], while the body’s internal pH is near neutral. Historically, the physiological function of an acidic skin surface pH was thought to provide protection (defense) against micro-organisms [4]. However, since the early 2000’s the skin surface pH and maintenance thereof has been implicated in playing an important role in stratum corneum integrity and cohesion and the regulation of epidermal barrier homeostasis and antimicrobial defense mechanisms [4, 5]. Interest in the skin’s pH is also attributed to numerous diseases affecting skin pH, including acne and eczema [4]. For example, persons with filaggrin mutations and atopic eczema have significantly higher skin pH values than individuals not carrying filaggrin mutations [6] (Danby and Cork, as well as Bigliardi, in this volume).

In chemistry, pH is defined as the – log [H⁺] concentration of a pure aqueous solution. With skin surface pH measurement “apparent skin pH” is measured, since the skin is not an aqueous solution as H⁺ ions are released by lipids and other compounds present on the skin into the water applied to the skin with the electrode [2, 7, 8]. Several non-invasive methods for measuring skin surface pH have been developed over the past 90 years. In this chapter, we summarise the factors that influence skin surface pH and its measurement as well as the different measurement methods for skin surface pH, with specific emphasis on the classic planar glass electrode method. Also, we provide practical guidance for measurement of skin surface pH in clinical and non-clinical settings using the planar glass electrode method. Given the simplicity of this instrument, skin surface pH can be monitored routinely as part of a skin health program.