Abstract
Background/Aims: The effects of a 10% α-hydroxy acid (AHA) oil/water (O/W) emulsion on the pH of human skin surface (pH<sub>ss</sub>) and stratum corneum (SC; pH<sub>sc</sub>) were evaluated in vivo. Methods: The AHA O/W emulsion was applied to an area on the volar forearm of male volunteers (n = 12), and then wiped off after 10 min. Prior to application and over the following 3 h, the pH<sub>ss</sub> was measured. We used glass electrode measurements and time domain dual lifetime referencing (tdDLR) with luminescent sensor foils. In another experiment (n = 5), the impact of the AHA O/W emulsion on the pH<sub>sc</sub> gradient was measured by tape stripping of the SC of the volar forearm after application of the AHA O/W emulsion. Results: Compared with pH<sub>ss</sub> values prior to treatment [5.2 ± 1.7 (tdDLR) or 4.8 ± 0.5 (electrode)], the pH<sub>ss</sub> was significantly reduced 10 min after application [4.0 ± 0.3 (tdDLR) or 4.1 ± 0.1 (electrode)] and the pH<sub>ss</sub> remained significantly reduced over the measurement period of 3 h [after 3 h: 4.4 ± 0.2 (tdDLR) or 4.5 ± 0.3 (electrode)]. The AHA O/W emulsion significantly reduced the pH<sub>sc</sub> even down to deep layers of the SC. Conclusion: After a 10-min application time, the 10% AHA O/W emulsion reduces the pH<sub>ss</sub> (for at least 3 h) and pH<sub>sc</sub> in deep layers of the SC.
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