A sequential tape stripping approach for the assessment of the impact of personal cleansing products on the stratum corneum surface layers' acid mantle properties and antimicrobial defense.

BACKGROUND: Stratum corneum (SC) plays a critical role in skin barrier function for protection and defense in nature. The acidic skin pH, which is also known as the acid mantle, is very important in fighting against outer environmental threats, especially, bacteria. Furthermore, recent research has shown that the transient bacteria could potentially penetrate into deeper layer of the SC down to a few micrometers while posing an additional threat to the deeper layers of the skin. AIM: To develop a sequential tape stripping method for assessing the impact of personal cleansing product on the SC surface layers' acid mantle properties and antimicrobial defense against transient bacteria. METHODS: Fifty-five subjects were recruited. High pH soap-based Product 1 and low pH synthetic surfactant-based Product 2 were applied on the left and right forearms of each subject. Sequential tape stripping was performed on the same spots to access multiple layers of the skin SC. Both antimicrobial defense property and skin pH of different skin layers were evaluated at baseline and 12 h after treatment. RESULTS: The skin's antimicrobial defense was significantly higher 12 h after treatment of the low pH Product 2 as compared to the treatment of high pH Product 1. In fact, this trend was consistent across all three skin layers (Layer 1 to Layer 3) as measured in this study (p < 0.01). Furthermore, the skin surface pH of Layer 1 and Layer 3 were also lower 12 h after the treatment of low pH Product 2 as compared to that of the high pH Product 1 (p < 0.01). CONCLUSION: The results of this investigation demonstrated the benefits of 12-h long lasting and deeper protection of SC acid mantle properties and antimicrobial defense using a low pH skin cleansing product as compared to a high pH product.

Mechanistic Skin Modeling of Plasma Concentrations of Sunscreen Active Ingredients Following Facial Application.

Sunscreen products constitute two distinct categories. Recreational sunscreens protect against high-intensity, episodic sun exposure, often applied over the entire body. In contrast, facial sunscreen products are designed for sub-erythemal, low-intensity daily sun exposure. Such different exposures necessitate distinctive product safety assessments. Building on earlier methods for predicting dermal disposition, a mechanistic model was developed to simulate plasma concentrations of seven organic sunscreen active ingredients: avobenzone, ensulizole, homosalate, octinoxate, octisalate, octocrylene, and oxybenzone, following facial application. In vitro permeation testing (IVPT) was performed with two different vehicles using a subset of the UV filters. These IVPT results, in addition to previously published IVPT data and published in vivo Maximal Usage Trial (MUsT) data for the UV filters, were used to train the mechanistic dermal model via a Bayesian Markov chain Monte Carlo (MCMC) method. An external validation of the trained model with real-world in vivo datasets demonstrated that the model's predicted UV filter plasma concentrations align well with experimental measurements and capture the observed inter-individual variability. Predictions of steady-state UV filter plasma concentrations under facial application scenarios at 5% concentration and at the maximal allowable concentrations were then generated by the trained model. Oxybenzone had the greatest predicted plasma concentration following facial application. Homosalate and octisalate predictions had high uncertainty associated with the absence of data. Several application scenarios pertaining to avobenzone, ensulizole, octocrylene and octinoxate were identified in which median plasma concentration levels were at 0.5 ng/ml or below when applied in the recreational or facial product. Model limitations include uncertainty in vehicle/water partitioning, formulation metamorphosis, and UV filter systemic clearance, all of which can be refined with additional data. For UV filters, limiting exposure to facial application reduces human safety concerns based on FDA established thresholds.

The vitamin A ester retinyl propionate has a unique metabolic profile and higher retinoid-related bioactivity over retinol and retinyl palmitate in human skin models.

Human skin is exposed daily to environmental stressors, which cause acute damage and inflammation. Over time, this leads to morphological and visual appearance changes associated with premature ageing. Topical vitamin A derivatives such as retinol (ROL), retinyl palmitate (RPalm) and retinyl propionate (RP) have been used to reverse these changes and improve the appearance of skin. This study investigated a stoichiometric comparison of these retinoids using in vitro and ex vivo skin models. Skin biopsies were treated topically to compare skin penetration and metabolism. Treated keratinocytes were evaluated for transcriptomics profiling and hyaluronic acid (HA) synthesis and treated 3D epidermal skin equivalents were stained for epidermal thickness, Ki67 and filaggrin. A retinoic acid receptor-alpha (RARα) reporter cell line was used to compare retinoid activation levels. Results from ex vivo skin found that RP and ROL have higher penetration levels compared with RPalm. RP is metabolized primarily into ROL in the viable epidermis and dermis whereas ROL is esterified into RPalm and metabolized into the inactive retinoid 14-hydroxy-4,14-retro-retinol (14-HRR). RP treatment yielded higher RARα activation and HA synthesis levels than ROL whereas RPalm had a null effect. In keratinocytes, RP and ROL stimulated similar gene expression patterns and pathway theme profiles. In conclusion, RP and ROL show a similar response directionality whereas RPalm response was inconsistent. Additionally, RP has a consistently higher magnitude of response compared with ROL or RPalm.

In Vitro Penetration of Petrolatum in Stratum Corneum from Bodywash Formulation.

Petrolatum is a mixture of hydrocarbons that is widely used as a moisturizer. It is incorporated in bodywash formulations to help hydrate and maintain healthy skin appearance. The aim of this study was to investigate skin deposition and penetration of petrolatum from an experimental bodywash system consisting of petrolatum in vitro. Experiments were performed using cadaver split-thickness skin and Franz diffusion cells. Radiolabeled 14C-dotriacontane (C32-alkane) was used as a model permeant for petrolatum. The bodywash was applied on the skin and subsequently rinsed. At predetermined time points, the skin was wiped to remove the residual material on the surface, and tape-stripping was performed. Petrolatum was observed to deposit from the bodywash when applied on split-thickness skin with simulated rinsing. Petrolatum then penetrated into the stratum corneum and was detected at the depth of 12 tape-stripping and in the epidermis. The bodywash formulation could provide significant deposition and penetration of petrolatum into the stratum corneum at 1-72 hours postapplication.

Comparing Surfactant Penetration into Human Skin and Resulting Skin Dryness Using In Vivo and Ex Vivo Methods.

Numerous tests have been developed to estimate a surfactant's mildness in rinse-off formulations. In this study, mixed surfactant systems were examined for their impact on surfactant penetration into the skin and skin hydration using in vivo and ex vivo methods. A forearm controlled application test (FCAT) was conducted, and skin hydration was evaluated using corneometry and visual dryness grading. Tape strip and cup scrub extractions were completed within the FCAT to examine the penetration of five individual surfactants into the skin in vivo. The ratio of surfactant mass extracted by five pooled tape strips to surfactant mass extracted by cup scrubs was found to be in the range of 40-59%. Furthermore, cup scrub collection and analysis was less time-consuming and less expensive to conduct than tape stripping. Thus, we recommend cup scrub extraction as a suitable substitute for tape stripping in future surfactant skin penetration analyses. In vivo results were compared with ex vivo 14C-sodium dodecyl sulfate (14C-SDS) penetration into human cadaver skin from the same surfactant systems. In vivo measurements conducted in the FCAT, including corneometer reading, visual dryness score, and individual surfactant (sodium laureth (1) ether sulfate and cocamidopropyl betaine) extracted from the skin, were found to correlate well with 14C-SDS penetration into the skin ex vivo for anion-based surfactant systems. Thus, 14C-SDS skin penetration may be a useful preclinical test for skin dryness induced by rinse-off products containing anionic surfactants.

Development of a preclinical surfactant skin penetration assay to reflect exposure times typical of consumer use.

Mixed surfactant and surfactant-polymer compositions have been reported to decrease surfactant deposition onto and penetration into the skin relative to single surfactant compositions, potentially improving the mildness of the product. Previous workers in this area [see Moore et al., J. Cosmet. Sci.54:29-46 (2003), and subsequent publications] employed a procedure in which excised porcine skin was exposed to a surfactant solution containing radiolabeled sodium dodecyl sulfate (14C-SDS) for 5 h. We have developed an improved SDS penetration assay using excised human skin that reflects typical consumer exposure times for rinse-off products. Using the new protocol, we were able to see a significant decrease in 14C-SDS penetration from a sodium lauryl sulfate (SLS)/polyethylene oxide composition applied to excised skin for either 2 or 10 min, as compared to SLS only. Furthermore, differences between the SDS penetration patterns on porcine skin and human skin were seen with a second SLS/polymer system; consequently, we do not recommend porcine skin for routine mildness screening by 14C-SDS penetration.