Impact of dermal emulsions containing diacyl phospholipids, mono acyl phospholipids, sodium lauryl ether sulfate and polysorbate 80 in combination with UVA irradiation on human skin physiology in vivo: A pilot study.

Stratum corneum (SC) barrier damage through dermally applied substances with irritation potential is well documented. However, little information about the impact of combined chemical and physical aggressors on human skin physiology in vivo exists. Thus, the aim of this study was to evaluate SC alterations caused by treatment with o/w emulsions stabilized by diacyl and monoacyl phospholipids and control surfactants with and without UVA irradiation. Biophysical skin parameters of eight healthy volunteers were examined on the volar forearm 1 h and 24 h after occlusive treatment with Finn chambers using skin probes to analyze transepidermal water loss (TEWL), pH, hydration, erythema and melanin index. Quantitative confocal Raman spectroscopy (CRS) was employed to non-invasively collect depth-resolved skin spectra. After recovery, the treatment was repeated in combination with 20 J/cm2 UVA exposure. In addition, ex vivo studies with similar protocol (semi-occlusive treatment) were conducted to complement in vivo data. Results showed increased TEWL and skin surface pH 1 h after sodium lauryl ether sulfate (SLES) emulsion treatment (TEWL: +7.7% to +10.2%; pH: +16.6% to +17.5%), accompanied by reduced SC hydration and natural moisturizing factor (NMF) content (hydration: -32.9% to -36.0%; NMF: -27.1% to -27.6%) compared to a diacyl phospholipid emulsion and the controls (water, polysorbate 80 emulsion), irrespective of UVA irradiation. Surprisingly, mono acyl phospholipids had lower impact than anticipated regarding their high emulsifying power, suggesting skin-friendliness when used in emulsion products. Comparative studies ex vivo showed limited potential to detect biophysical differences in human skin observed in vivo.