MEASUREMENT OF pH OF THE SKIN SURFACE1 2

In 1923, Sharlit and Seheer (1) published a paper entitled "The Hydrogen-Ion Concentration of the Healthy, Intact Skin," in which they discussed in detail the meaning of hydrogen-ion concentration and pH, and showed how the entire concept of hydrogen-ion concentration is a part of the general theory of electrolytic dissociation. They stated that the only method available at that time for measuring the hydrogen-ion concentration of the skin was the colorimetric method and, using this method, arrived at an approximate average pH of 5.5. In a series of papers beginning in 1928, Schade and Marchionini (2) described an electrometric method, using a specially designed hydrogen electrode called the "Glockenelektrode." With this electrode, they found that the pH of the skin surface varied from 3.0 to 5.0 and attributed the variation to such factors as amount of sweating, evaporation of sweat and actual chemical differences in the composition of the sweat itself from area to area. In one of these papers, a quinhydrone electrode was also described. Lustig and Perutz (3) in 1930 used Wulif indicator foils to measure the pH of a drop of distilled water after it had remained in contact with the skin for five minutes. They found the pH of the skin surface to vary from area to area and from individual to individual, with an average range of 5.3 to 6.5. Levin and Silvers (4), using a microquinhydrone electrode, found the pH of the normal skin to vary from 5.0 to 5.3. They found that the axillae and the interdigital areas had a higher pH. The methods used by the above workers include two colorimetric and the two more commonly used electrometric methods. In the colorimetric methods, the color of the skin and the oxidizing and reducing agents on the skin surface alter the shade of the indicator solution or foil so that matching with a standard becomes difficult. The limit of accuracy of any colorimetric method is 0.2 pH. Both the quinhydrone and the hydrogen electrode methods are subject to errors brought about by the presence of oxidizing and reducing agents, proteins and