Читать книгу pH of the Skin: Issues and Challenges - Группа авторов - Страница 17

The first investigations dealing with the degree of acidity on skin surface were made by way of colorimetry [10]. Accuracy was limited and the application impractical. In their basic work on skin pH, Schade and Marchionini [15] used an electrometering device – the quinhydrone electrode (redox electrode). First experiments with “flat” glass electrodes [64, 65] were reported in 1938. Their use has become the current standard and since then brought together an enormous amount of information on skin surface pH as a function of endogenous, exogenous, and environmental factors. Since the beginning of skin surface pH recording, some authors repeatedly point out that the pH measurement and the measurement process per se represent major challenges. In the last decade, some groups have taken the effort to develop guidelines for the in vivo assessment of skin surface pH and made recommendations for measurement, measurement interpretation, and data reporting to promote a more universal/standardized methodology to be followed, which if done would make comparison of data possible [66, 67]. However, the relevance of the various experimental conditions still remains unclear and has not been investigated in detail. Already Schade and Marchionini in 1928 mentioned the difficulties with the pH measurement in connection with the rinsing of the electrode and the skin. This and many other issues have been addressed in the guidance though more systematic testing is urgently needed to better understand the pH measurement of the microenvironment itself between the glass electrode and the skin. Too little attention is devoted to the fact that the measurement represents only the pH of the microenvironment between the glass electrode and the skin and may therefore be different from the actual skin surface pH or the pH of the underneath layers. It is therefore advisable to bear in mind that the use of any topical products may significantly affect the measurement [68]. This applies also to the water including its quality that is applied for skin surface pH measurement. The potential “aging” of the electrodes and its relevance to measurement quality is also an area in need of investigation to improve guidance. In the future, major efforts are needed to evaluate these and other potentially relevant factors to further improve the measuring certainty.

Other approaches for the measurement of the skin surface pH have been proposed (e.g., microelectrodes, pH-sensitive fluorescent dyes followed by confocal laser microscopy, or electron spin microscopy imaging). However, these have not yet become routinely operational [11, 12, 69–72].