Impact of a pH 5 Oil-in-Water Emulsion on Skin Surface pH

Background: Human skin surface has a physiologically acidic pH (pH_ss). In cases of increased pH_ss, the acidity of the skin can be restored by topical formulations. We tested a pH 5 oil-in-water (O/W) emulsion for pH_ss regeneration and stabilization. Methods: We performed 2 experiments with 10 female study subjects in each. In both experiments, 2D imaging with luminescent sensor foils was used to determine pH_ss. Alkalization was reached by washing the volar forearm with a soap bar and warm running tap water for 20 min. Experiment 1: after defining the baseline pH_ss, we alkalized the respective area and measured pH_ss over a duration of 5 h, while applying emulsion every hour. Experiment 2: study subjects used the emulsion twice daily for 1 week. Then, pH_ss was measured before and after 5 min of washing a treated and an untreated area on the volar forearm. Results: (1) 5 h after alkalization, the treated arm showed a significantly lower pH_ss than the untreated one (5.87 ± 0.03 vs. 6.05 ± 0.03); (2) after washing, the treated area had a significantly lower pH_ss than controls (6.13 ± 0.03 vs. 6.27 ± 0.05). Conclusions: The tested pH 5 O/W emulsion seems to improve regeneration and stabilization of pH_ss.
Skin Pharmacol Physiol 2017;30:292-297