Comparison of two pH meters used for skin surface pH measurement: the pH meter 'pH900' from Courage & Khazaka versus the pH meter '1140' from Mettler Toledo

Background/aims: Measurement of skin surface pH is used in clinical research to evaluate hazardous shifts in pH following external exposures and to evaluate the state of diseased skin with acute or chronic changes. It is therefore important to measure skin surface pH as precisely as possible. The aim of this study was to compare two commercially available pH meters used for skin surface pH measurement, to reveal differences between them in measured skin pH on the forearm. Methods: The first pH meter (pH900) had a pointed electrode and a stabilisation period of 3 s. The second pH meter (pH meter 1140) had a circular electrode and no fixed stabilisation period. Twelve healthy subjects (6 male and 6 female Caucasians) entered the study. The pH measurements were performed once an hour from 8 a.m. to 3 p.m. on both forearms in five areas from the elbow to the "wristwatch" zone. In each area. three measurements were performed next to each other with both pH meters (15 measurements per arm per hour per pH meter). Results: The pH900 has a higher measuring level and a higher variation than the pH meter 1140. Conclusion: A skin surface pH meter with a circular electrode and with no fixed stabilisation period is preferable. It is recommended that the pH meter be allowed to stabilise for at least 7 s before the result is read.