Cleansing, dehydrating, barrier-damaging and irritating hyperaemising effect of four detergent brands: comparative studies using standardised washing models

A comparative study of the in vitro permeation of 2-phenoxyethanol in the skin PAMPA model and mammalian skin

For permeation studies that use excised skin, experimental data may show variability associated with the use of biological tissues. As a consequence, achieving reproducible results and data interpretation may be challenging. The skin parallel artificial membrane permeability assay (skin PAMPA) model has been proposed as a high-throughput tool for predicting skin permeation of chemicals. A number of skin cleansing wipe formulations for the diaper area of infants contain 2-phenoxyethanol (PE) as a preservative and cetylpyridinium chloride (CPC) as a surfactant with antimicrobial activity. However, information regarding cutaneous absorption of PE and CPC in the scientific literatures is remarkably limited. The main aim of the present study was to assess the suitability of the skin PAMPA model for prediction of skin permeation of PE. A secondary aim was to investigate the influence of CPC on the dermal absorption of PE. PE (1 % w/w) was prepared in two vehicles, namely propylene glycol (PG) and water-PG (WP). Permeability of PE was investigated in vitro using the skin PAMPA membrane, porcine skin and human skin under finite dose conditions. The highest permeation of PE was observed for the water-PG preparation with 0.2 % w/w of CPC. This finding was consistently observed in the skin PAMPA model and in Franz cell studies using porcine skin and human skin. Permeation of CPC was not detected in the three permeation models. However, permeation of PE increased significantly (p < 0.05) in the presence of CPC compared with formulations without CPC. When comparing the skin PAMPA data and the mammalian skin data for the cumulative amount of PE permeated, the r² values for PAMPA-porcine skin and PAMPA-human skin were 0.84 and 0.89, respectively. The findings in this study demonstrate the capability of the skin PAMPA model to differentiate between various doses and formulations and are encouraging for further applications of this model as a high throughput screening tool in topical formulation development.

Glycerol and natural sugar-derived complex modulate differentially stratum corneum water-binding properties and structural parameters in an in vitro Raman-desorption model

The epidermal protective functions are closely associated with skin hydration homeostasis. The understanding of different states of water binding is a rising concept in assessing topically applied formulations and their interaction within the stratum corneum (SC). In addition to global water content, primary bound water, partially bound water, and unbound water and barrier-related lipid lateral packing and protein secondary structure can be measured by Raman spectroscopy. This study aimed to establish an in vitro SC model to evaluate differences in the efficacy of a natural sugar-derived complex in combination with glycerol and a botanical extract in modulating SC water binding and structural proteins and barrier lipids. These compounds were selected due to their water-binding and soothing properties. The SC water profiles were assessed at the surface and in 8 μm SC depth. After a 12-hour hyperhydration and subsequent product incubation the measurements were performed during a 6 hours desiccation phase. The maximal water caption and the time until reaching a steady state are measured as well as water retention and resistance against water loss. Global water content, partially bound, and unbound water, as well as lipid and protein structures were assessed with confocal Raman microspectroscopy. Both the natural sugar-derived mixture and more pronounced, the same mixture with additional glycerol increased all three water-binding parameters at the surface and in 8 μm SC depth at the beginning and during the desiccation phase. Further addition of botanical extract did not result in an additional increase of the water-binding. All three formulations showed an increase in the lipid lateral packing values prevented the protein alteration as measured by β-sheets signal compared to blank. The present model is suited for screening studies comparing the specific effects of different compounds on hydration states. The natural sugar-derived mixture Aquaxyl showed evidence for an improvement of all SC hydration states, lipid and protein structure which was further enhanced by the addition of glycerol 5%. This improvement was evidenced at the surface and within the SC for all hydration-related parameters, and the lipid as well the protein structures. The addition of botanical extract phytoessence blue daisy did not show further improvement.

Stratum Corneum Function: A Structural Study with Dynamic Synchrotron X-ray Diffraction Experiments

Studies on the effectiveness of substances such as drugs and cosmetics that act on the skin require structural evidence at the molecular level in the stratum corneum to clarify their interaction with intercellular lipid and soft keratin. For this purpose, when applying the substances to the stratum corneum X-ray diffraction experiment is one of the powerful tools. To detect minute structural changes in a stratum corneum sample, using a "solution cell", dynamic synchrotron X-ray diffraction measurements were performed when applying aqueous solution of the substances to the stratum corneum: (1) It was found that a surfactant, sodium dodecyl sulfate, significantly disrupted the long-period lamellar structure. (2) To study the effects of water, structural modifications of the short-period lamellar structure and the soft keratin in corneocytes were measured as a function of time. At the initial water content of 15 wt%, the spacings of the short-period lamellar structure and the soft keratin increased toward those at the water content of 25 wt%, that is a key water content in the stratum corneum. (3) Nanoparticles composed of assembly of amphiphilic molecules are one of the leading pharmaceutical formulations. When the nanoparticles were applied, a new assembly of amphiphilic molecules originated from the nanoparticle appeared. This phenomenon suggests that the formation of the new assembly at the surface of skin is concerned with the release of the drug from the nanoparticles. (4) When ethanol was applied to the stratum corneum, only the liquid state in the intercellular lipid matrix was dissolved. After the removal of ethanol from this stratum corneum, the ordered hydrocarbon-chain packing structures appeared. From this fact we would propose that the liquid state region is the main pathway for hydrophobic drugs with a small molecular weight in connection with the so-called 500 Da rule. Here, not only the technique but also the background to these studies and the characteristic results obtained from these studies are explained.

Development of a standardized testing procedure for assessing the irritation potential of occupational skin cleansers

BACKGROUND

Frequent skin cleaning fulfils the definition of occupational 'wet work'. Standardized methods are required to assess the irritation potential of workplace cleansers.

OBJECTIVES

To develop a standardized procedure for testing the irritation potential of occupational skin cleansers.

METHODS

In this single-blind, single-centre trial in 25 healthy volunteers, the irritation potential of five generic reference cleansers was tested by three-times-daily washing with an automated skin cleaning device for 4 days, and quantification of cumulative skin barrier damage was performed by visual scoring, chromametry, transepidermal water loss TEWL, and corneometry. For two cleansers, reproducibility of the irritancy assessment was assessed. Furthermore, the irritation induced by four commercial workplace skin cleansers was studied.

RESULTS

Whereas no significant changes were observed for any of the tested cleansers by either visual scoring or chromametry, significant increases in TEWL and significant decreases in stratum corneum hydration were found for all cleansers. Cleansers differed significantly in their irritation potential. On retesting of two cleansers, the first results were confirmed. Among the four commercial cleansers, one that was claimed to be mild was found to be disproportionally irritant.

CONCLUSIONS

The presented model for testing cleansing preparations allows a highly controlled, practically relevant and reproducible irritancy assessment of occupational skin cleansers.

Cleansing formulations that respect skin barrier integrity

Surfactants in skin cleansers interact with the skin in several manners. In addition to the desired benefit of providing skin hygiene, surfactants also extract skin components during cleansing and remain in the stratum corneum (SC) after rinsing. These side effects disrupt SC structure and degrade its barrier properties. Recent applications of vibrational spectroscopy and two-photon microscopy in skin research have provided molecular-level information to facilitate our understanding of the interaction between skin and surfactant. In the arena of commercial skin cleansers, technologies have been developed to produce cleansers that both cleanse and respect skin barrier. The main approach is to minimize surfactant interaction with skin through altering its solution properties. Recently, hydrophobically modified polymers (HMPs) have been introduced to create skin compatible cleansing systems. At the presence of HMP, surfactants assemble into larger, more stable structures. These structures are less likely to penetrate the skin, thereby resulting in less aggressive cleansers and the integrity of the skin barrier is maintained. In this paper, we reviewed our recent findings on surfactant and SC interactions at molecular level and provided an overview of the HM technology for developing cleansers that respect skin barrier.

Quantitative analysis of surfactant deposits on human skin by liquid chromatography/electrospray ionisation tandem mass spectrometry

Surfactants are commonly used as cleansing agents and yet there are concerns that they may also have a role in skin irritation. The lack of suitable methods for the quantitative and qualitative analysis of surfactant deposition on skin has hindered the in-depth investigation of such effects. Here, we report the application of reversed-phase liquid chromatography/electrospray ionisation tandem mass spectrometry (LC/ESI-MS/MS) assays for two surfactants commonly used in consumer products, namely sodium lauryl ether sulfate (SLES) and laurylamidopropyl betaine (LAPB), to a baseline study aiming to assess deposition levels on human skin. The linearity of the assays was established at 3-20 ng, with coefficient of variation below 5%. The detection limits were 100 pg for LAPB and 1 ng for SLES; quantitation limits were 500 pg for LAPB and 2.5 ng for SLES. The baseline study was conducted using a panel of 40 healthy volunteers. Skin extract samples were taken in triplicate from forearms, using ethanol. SLES was detected on most volunteers, with 75% of them having SLES deposits in the range of 100-600 ng/cm(2). LAPB was detected on the skin of all volunteers with 85% of them having deposit levels within the concentration range of 1-100 ng/cm(2). These results demonstrate the extent to which commonly used surfactants remain on the skin during the day. The analytical methods reported here can be applied to the investigation of surfactants in relation to general skin condition and to the development and optimisation of new consumer wash products.

Effect of standardized skin care regimens on neonatal skin barrier function in different body areas

The effect of topical skin care products on neonatal skin barrier during first 8 weeks of life has not been scientifically evaluated. In a prospective, randomized clinical study, we compared the influence of three skin care regimens to bathing with water on skin barrier function in newborns at four anatomic sites. A total of 64 healthy, full-term neonates (32 boys and 32 girls) aged <48 hours were randomly assigned to four groups receiving twice-weekly: WG, bathing with wash gel (n = 16); C, bathing and cream (n = 16); WG + C, bathing with wash gel plus cream (n = 16); and B, bathing with water (n = 16). Transepidermal water loss, stratum corneum hydration, skin pH, sebum were measured on day 2, week 2, 4, 8 of life on front, abdomen, upper leg, and buttock. Skin condition was scored and microbiologic colonization was documented. After 8 weeks, group WG + C showed significantly lower transepidermal water loss on front, abdomen, and upper leg as well as higher stratum corneum hydration on front and abdomen compared with group B. Similarly, group C showed lower transepidermal water loss and higher stratum corneum hydration on these body regions. Group WG revealed significantly lower pH on all sites compared with group B at week 8. No differences in sebum level, microbiologic colonization and skin condition score were found. Skin care regimens did not harm physiologic neonatal skin barrier adaptation within the first 8 weeks of life. However, significant influence of skin care on barrier function was found in a regional specific fashion.

Skin capacitance imaging and corneosurfametry. A comparative assessment of the impact of surfactants on stratum corneum

Silicon image sensor (SIS) technology was recently introduced as an innovative tool (SkinChip, L'Oréal) providing sensitive imaging of the skin capacitance. This method can detect discrete focal variations in skin surface hydration, and thus early discrete manifestations of skin irritation induced by surfactants. In the present in vivo study, 2 neat and diluted shampoos, and 5% and 10% sodium laurylsulfate solutions were tested on human skin. Each surfactant solution was gently rubbed on the skin using wet hair wicks mimicking the casual use of a shampoo on the scalp. Clinical and SIS evaluations were carried out. In addition, the same products were tested using the ex vivo corneosurfametry bioassay performed on human stratum corneum (SC) harvested by cyanoacrylate skin surface strippings. The colourimetric index of mildness (CIM) was measured on these samples. The product reactivity with the SC was recognized by darker skin capacitance images, and by both lowered SkinChip-generated values and lowered CIM values. The extent in changes varied according to the nature of the test products and their concentrations. The SkinChip image changes likely corresponded to the acute surfactant-induced water swelling of the corneocytes. Skin capacitance imaging and corneosurfametry allow to disclose discrete surfactant-induced alterations of corneocytes.