The pH of the stratum corneum is slightly acidic (mean 4.9) and tightly regulated. This is important for antimicrobial defense and the formation of the physical barrier. The acidic pH inhibits the growth of pathogenic Staphylococcus aureus and enables optimal activity of enzymes for lipid synthesis, epidermal differentiation and desquamation. Here we asked whether topical application of an oil-in-water emulsions adjusted to pH 4 or pH 5.8 and the untreated control influence biophysical markers and mechanical stability of the skin barrier, Stratum corneum morphology and inflammation. Twenty-four healthy volunteers aged 18 to 75 years were treated in a randomized way on the lower arms for 28 days; pH, TEWL, SC hydration, mechanical stability, corneocyte size and inflammation were recorded. After 28 days, skin surface pH was significantly more reduced by the pH 4 compared to the pH 5.8 emulsion. TEWL as a marker of skin barrier function was slightly reduced by both emulsions. SC hydration was significantly increased to the same level by both emulsions. The number of D-Squame® tape-strips to disrupt the skin barrier to a threefold increase in TEWL as a marker for skin integrity was significantly increased by both emulsions compared to untreated control, but slightly more by the pH 4 emulsion. Inflammation after tape-stripping as determined by clinical grading of erythema was considerable reduced by the pH 4 emulsion, and IL-1α protein expression was significantly reduced by both emulsions, but the reduction was higher with the pH 4 preparation. The size of corneocytes attached to the tape-strips as a marker for epidermal differentiation and desquamation was significantly increased after treatment with the pH 4 compared to the pH 5.8 emulsion and the control. In summary, treatment with a pH 4 emulsion positively influenced SC pH, TEWL, SC hydration, epidermal differentiation/desquamation resulting in increased mechanically stability and reduced inflammation against tape-stripping induced irritation.

Skin barrier integrity is enhanced after topical application of emulsions with an acidic pH