Human skin surface lipid film: an ultrastructural study and interaction with corneocytes and intercellular lipid lamellae of the stratum corneum

Methods for the characterisation of dermal uptake: Progress and perspectives for organophosphate esters

Organophosphate esters (OPEs) are a group of pollutants that are widely detected in the environment at high concentrations. They can adversely affect human health through multiple routes of exposure, including dermal uptake. Although attention has been paid to achieving an accurate and complete quantification of the dermal uptake of OPEs, existing evaluation methods and parameters have obvious weaknesses. This study reviewed two main categories of methodologies, namely the relative absorption (RA) model and the permeability coefficient (PC) model, which are widely used to assess the dermal uptake of OPEs. Although the PC model is more accurate and is increasingly used, the most important parameter in this model, the permeability coefficient (Kp), has been poorly characterised for OPEs, resulting in considerable errors in the estimation of the dermal uptake of OPEs. Thus, the detailed in vitro methods for the determination of Kp are summarised and sorted. Furthermore, the commonly used skin membranes are identified and the factors affecting Kp and corresponding mechanisms are discussed. In addition, the experimental conditions, conclusions, and available data on Kp values of the OPEs are thoroughly summarised. Finally, the corresponding knowledge gaps are proposed, and a more accurate and sophisticated experimental system and unknown Kp values for OPEs are suggested.

Seborrheic dermatitis: topical therapeutics and formulation design

Seborrheic dermatitis (SD) is a common dermatological disorder with symptoms that include skin flaking, erythema and pruritus. This review discusses the topical products available for treating SD, which target several aspects of disease pathobiology, including cutaneous microbial dysbiosis (driven by Malassezia yeast), inflammation, sebum production and skin barrier disruption. Among the various treatments available, zinc pyrithione (ZnPT) based products that exhibit anti-fungal action are the market leaders. A skin compartment approach is presented here for combining ZnPT exposure information with threshold levels for anti-fungal efficacy and toxicity, overall providing a comprehensive picture of ZnPT therapeutics and safety. While Malassezia yeast on the surface are effectively targeted, yeast residing beyond the superficial follicle may not receive adequate ZnPT for anti-fungal effect forming the basis for skin re-colonisation. Levels entering systemic circulation from topical delivery are well below toxic thresholds, however the elevated zinc levels within the viable epidermis warrants further investigation. Strategies to improve formulation design can be broadly classified as influencing 1) topical delivery, 2) therapeutic bioactivity, 3) skin mildness, and 4) sensory attributes. Successful SD treatment ultimately requires formulations that can balance efficacy, safety, and consumer appeal.

No skin off your back: the sampling and extraction of sebum for metabolomics

INTRODUCTION

Sebum-based metabolomics (a subset of "sebomics") is a developing field that involves the sampling, identification, and quantification of metabolites found in human sebum. Sebum is a lipid-rich oily substance secreted by the sebaceous glands onto the skin surface for skin homeostasis, lubrication, thermoregulation, and environmental protection. Interest in sebomics has grown over the last decade due to its potential for rapid analysis following non-invasive sampling for a range of clinical and environmental applications.

OBJECTIVES

To provide an overview of various sebum sampling techniques with their associated challenges. To evaluate applications of sebum for clinical research, drug monitoring, and human biomonitoring. To provide a commentary of the opportunities of using sebum as a diagnostic biofluid in the future.

METHODS

Bibliometric analyses of selected keywords regarding skin surface analysis using the Scopus search engine from 1960 to 2022 was performed on 12th January 2023. The published literature was compartmentalised based on what the work contributed to in the following areas: the understanding about sebum, its composition, the analytical technologies used, or the purpose of use of sebum. The findings were summarised in this review.

RESULTS

Historically, about 15 methods of sampling have been used for sebum collection. The sample preparation approaches vary depending on the analytes of interest and are summarised. The use of sebum is not limited to just skin diseases or drug monitoring but also demonstrated for other systemic disease. Most of the work carried out for untargeted analysis of metabolites associated with sebum has been in the recent two decades.

CONCLUSION

Sebum has a huge potential beyond skin research and understanding how one's physiological state affects or reflects on the skin metabolome via the sebaceous glands itself or by interactions with sebaceous secretion, will open doors for simpler biomonitoring. Sebum acts as a sink to environmental metabolites and has applications awaiting to be explored, such as biosecurity, cross-border migration, localised exposure to harmful substances, and high-throughput population screening. These applications will be possible with rapid advances in volatile headspace and lipidomics method development as well as the ability of the metabolomics community to annotate unknown species better. A key issue with skin surface analysis that remains unsolved is attributing the source of the metabolites found on the skin surface before meaningful biological interpretation.

Non-invasive human skin transcriptome analysis using mRNA in skin surface lipids

Non-invasive acquisition of mRNA data from the skin can be extremely useful for understanding skin physiology and diseases. Inspired by the holocrine process, in which the sebaceous glands secrete cell contents into the sebum, we focused on the possible presence of mRNAs in skin surface lipids (SSLs). We found that measurable levels of human mRNAs exist in SSLs, where the sebum protects them from degradation by RNases. The AmpliSeq transcriptome analysis was modified to measure SSL-RNA levels, and our results revealed that the SSL-RNAs predominantly comprised mRNAs derived from sebaceous glands, the epidermis, and hair follicles. Analysis of SSL-RNAs non-invasively collected from patients with atopic dermatitis revealed increased expression of inflammation-related genes and decreased expression of terminal differentiation-related genes, consistent with the results of previous reports. Further, we found that lipid synthesis-related genes were downregulated in the sebaceous glands of patients with atopic dermatitis. These results indicate that the analysis of SSL-RNAs is a promising strategy to understand the pathophysiology of skin diseases.

Inoue et al develop a non-invasive method of analyzing human skin mRNA using RNA in skin surface lipids collected with oil-blotting films. The authors outline the validation of this methodology and describe an application to determine transcriptome in skin surface lipids in patients with atopic dermatitis versus healthy skin.

A new device for the combined measurement of friction and through-thickness deformation on ex vivo skin samples

Skin irritation is a common phenomenon that becomes a real concern when caused by the use of medical devices. Because the materials used for the design of these devices are usually carefully selected for chemical compatibility with the skin, it is reasonable to assume that the irritations result from the mechanical interaction between the devices and the skin. The aim of this work was to develop a new device to study both the shear strains in the layers of the skin, using Digital Image Correlation (DIC), and the friction behaviour of ex vivo skin interacting with objects. Pig skin samples with various surface preparations were tested in friction experiments involving different contacting materials encountered in the conception of medical devices. The measure of the static and dynamic coefficients of friction as well as the length of adhesion has highlighted the great influence of skin surface conditioning on friction properties. Strain maps obtained through DIC provided insights into the impact of friction and adhesion effects on shear strain distribution in the skin as a function of depth beneath its surface.

Modeling the Percutaneous Absorption of Solvent-deposited Solids Over a Wide Dose Range

The transient absorption of two skin care agents, niacinamide (nicotinamide, NA) and methyl nicotinate (MN), solvent-deposited on ex vivo human skin mounted in Franz diffusion cells has been analyzed according to a new variation on a recently published mechanistic skin permeability model (Yu et al. 2020. J Pharm Sci 110:2149-56). The model follows the absorption and evaporation of two components, solute and solvent, and it includes both a follicular transport component and a dissolution rate limitation for high melting, hydrophilic solids deposited on the skin. Explicit algorithms for improving the simulation of transient diffusion of solvent-deposited solids are introduced. The simulations can account for the ex vivo skin permeation time course of both NA and MN over a dose range exceeding 4.5 orders of magnitude. The model allows one to describe on a mechanistic basis why the percutaneous absorption rate of NA is approximately 60-fold lower than that of its lower melting, more lipophilic analog, MN. It furthermore suggests that MN perturbs stratum corneum barrier lipids and increases their permeability while NA does not, presenting a challenge to molecular modelers engaged in simulating biological lipid barriers.

Questionnaire and Lactic Acid Sting Test Play Different Role on the Assessment of Sensitive Skin: A Cross-sectional Study

BACKGROUND

Questionnaires and lactic acid sting test (LAST) are two widely used methods to identify sensitive skin. However, the self-perceived sensitive skin by questionnaires was not consistent with the determination of LAST.

OBJECTIVE

The aim of the study was to measure the biophysical properties noninvasively of sensitive skin evaluated by questionnaire and LAST and to investigate their correlations with the scores of questionnaire and LAST.

METHODS

A total of 209 healthy Chinese females completed the study. Self-assessment questionnaire and LAST were both performed to identify sensitive skin. Epidermal biophysical properties, including skin hydration, transepidermal water loss (TEWL), sebum content, erythema index (EI), a* value, L* value, skin elasticity, and skin pH, were measured with noninvasive instruments.

RESULTS

The frequency of sensitive skin was 50.2% and 66.0% by questionnaire and LAST, respectively. Subjects with self-assessed sensitive skin had a slightly higher LAST positive rate. Skin hydration, sebum content, a* and EI values were significantly higher in the self-assessed sensitive skin group, while TEWL, a* and EI values increased but L* value decreased with significance in the LAST positive group. The LAST stingers among sensitive skin subjects had higher EI but not in the healthy skin subjects. In addition, questionnaire scores positively correlated with skin hydration, sebum content, a* and EI values, while a positive relationship of LAST scores with TEWL, a* and EI values was observed. The scores of questionnaire and LAST both negatively related to L* value.

CONCLUSION

Self-assessed questionnaire is associated with sensitive skin featured by oily and red face without impaired barrier function, whereas LAST is suitable to identify fragile skin barrier and enhanced blood flow on the face. Combination of both methods to diagnose sensitive skin might be more reliable.

Targeted Delivery of Zinc Pyrithione to Skin Epithelia

Zinc pyrithione (ZnPT) is an anti-fungal drug delivered as a microparticle to skin epithelia. It is one of the most widely used ingredients worldwide in medicated shampoo for treating dandruff and seborrheic dermatitis (SD), a disorder with symptoms that include skin flaking, erythema and pruritus. SD is a multi-factorial disease driven by microbiol dysbiosis, primarily involving Malassezia yeast. Anti-fungal activity of ZnPT depends on the cutaneous availability of bioactive monomeric molecular species, occurring upon particle dissolution. The success of ZnPT as a topical therapeutic is underscored by the way it balances treatment efficacy with formulation safety. This review demonstrates how ZnPT achieves this balance, by integrating the current understanding of SD pathogenesis with an up-to-date analysis of ZnPT pharmacology, therapeutics and toxicology. ZnPT has anti-fungal activity with an average in vitro minimum inhibitory concentration of 10-15 ppm against the most abundant scalp skin Malassezia species (Malassezia globosa and Malassezia restrica). Efficacy is dependent on the targeted delivery of ZnPT to the skin sites where these yeasts reside, including the scalp surface and hair follicle infundibulum. Imaging and quantitative analysis tools have been fundamental for critically evaluating the therapeutic performance and safety of topical ZnPT formulations. Toxicologic investigations have focused on understanding the risk of local and systemic adverse effects following exposure from percutaneous penetration. Future research is expected to yield further advances in ZnPT formulations for SD and also include re-purposing towards a range of other dermatologic applications, which is likely to have significant clinical impact.

Seasonal variations in the skin parameters of Caucasian women from Central Europe

BACKGROUND

The human skin is greatly affected by external factors such as UV radiation (UVR), ambient temperature (T), and air humidity. These factors oscillate during the year giving rise to the seasonal variations in the skin properties. The aim of this study was to evaluate the effect of seasons, environmental T, relative and absolute humidity on the skin parameters of Caucasian women, perform a literature review and discuss the possible factors lying behind the found changes.

MATERIALS AND METHODS

We measured stratum corneum (SC) hydration, transepidermal water loss (TEWL), sebum level, erythema index, and elasticity parameters R2 and R7 on the forehead and the cheek of Caucasian women from the Czech Republic throughout the year. We also performed a non-systematic literature review focused on the seasonal variations in these skin parameters.

RESULTS

We confirmed a well-documented low SC hydration and sebum production in winter. In spring, we found the lowest TEWL (on the forehead) and the highest SC hydration but also the highest erythema index and the lowest elasticity presumably indicating skin photodamage. For most of the skin parameters, the seasonal variations probably arise due to a complex action of different factors as we extensively discussed.

CONCLUSION

The data about the seasonal variations in the skin parameters are still highly inconsistent and further studies are needed for better understanding of the normal skin changes throughout the year.

Factor analysis approach unveils the influencing factors of dandruff in the normal teenage population

The aim of this study was to explore the main factors affecting the occurrence of dandruff in healthy people (nondisease-induced scalp desquamation). This study analyzed the fungal microbial diversity of the scalp in Chinese teenage volunteers and measured scalp sebum secretion, the scalp pH value, and scalp transepidermal water loss. The amount and size of dandruff were measured, and the main factors that influence dandruff in the normal population were identified using principal component analysis. The results showed that an increase in Malassezia restricta led to an increased amount of dandruff in the mild and moderate groups. Conversely, this was not found for individuals in the severe group, whose dandruff symptoms were influenced by scalp barrier function. In terms of dandruff area grouping, the pH value and the amount of sebum secretion were the main factors, with the barrier function and microbial diversity being secondary factors. Dandruff cosmetics should emphasize different treatments for different types of dandruff to achieve better antidandruff effects. The results of this study provide a new theoretical basis for the development of multiple targets for antidandruff agents aimed at the normal population.

Bioaccessibility of Drug Residues on Common Police Station Work Surfaces

The fraction of any surface-adsorbed contaminant available for absorption is considered the bioaccessible fraction. Applied previously to contaminants such as pesticides and heavy metals on surfaces such as soil, food and cosmetics, the term may also be used to describe the fraction of drug residue bound to work surfaces which may be mobilized via contact transfer with human skin. Police station work surfaces have been shown to commonly contain low levels of drug residues as thin films; however, no information is available on how readily these residues may be transferred to human skin during direct or glancing contact. A bioaccessibility study was undertaken in which jojoba oil and artificial sebum were used to mimic human sebum to identify how readily a mix of six licit and illicit drugs were transferred from three commonly used police station work surfaces. Transfer from surfaces was slightly greater for jojoba oil than sebum when using a direct pressure contact or a wiping motion. Generally, less than 5% of applied residues were recovered via direct contact, and up to 10% when a wiping motion was used to simulate a glancing contact. While swabbing of work surfaces with methanol provides a suitable environmental audit of drug residues present, it does not represent the bioaccessible fraction of residues available for contact transfer, and hence, absorption via skin or unintentional ingestion. The current study indicates that the ability of sebum to mobilize drug residues from thin films on work surfaces via casual contact is limited, and sebum may potentially assist in the preservation of residues on pitted work surfaces and on skin.

Mechanisms of lipid extraction from skin lipid bilayers by sebum triglycerides

Microsecond computations identify the pathways leading to the extraction of skin lipids by sebum triglycerides and the associated energetic costs.

Influence of the sebaceous gland density on the stratum corneum lipidome

The skin surface lipids (SSL) result from the blending of sebaceous and epidermal lipids, which derive from the sebaceous gland (SG) secretion and the permeability barrier of the stratum corneum (SC), respectively. In humans, the composition of the SSL is distinctive of the anatomical distribution of the SG. Thus, the abundance of sebum biomarkers is consistent with the density of the SG. Limited evidence on the influence that the SG exerts on the SC lipidome is available. We explored the differential amounts of sebaceous and epidermal lipids in areas at different SG density with lipidomics approaches. SC was sampled with adhesive patches from forearm, chest, and forehead of 10 healthy adults (8F, 2M) after mechanical removal of sebum with absorbing paper. Lipid extracts of SC were analysed by HPLC/(-)ESI-TOF-MS. In the untargeted approach, the naïve molecular features extraction algorithm was used to extract meaningful entities. Aligned and normalized data were evaluated by univariate and multivariate statistics. Quantitative analysis of free fatty acids (FFA) and cholesterol sulfate (CHS) was performed by targeted HPLC/(-)ESI-TOF-MS, whereas cholesterol and squalene were quantified by GC-MS. Untargeted approaches demonstrated that the relative abundance of numerous lipid species was distinctive of SC depending upon the different SG density. The discriminating species included FFA, CHS, and ceramides. Targeted analyses confirmed that sebaceous FFA and epidermal FFA were increased and decreased, respectively, in areas at high SG density. CHS and squalene, which are biomarkers of epidermal and sebaceous lipid matrices, respectively, were both significantly higher in areas at elevated SG density. Overall, results indicated that the SG secretion intervenes in shaping the lipid composition of the epidermal permeability barrier.

Enhancing glucose flux into sweat by increasing paracellular permeability of the sweat gland

Non-invasive wearable biosensors provide real-time, continuous, and actionable health information. However, difficulties detecting diluted biomarkers in excreted biofluids limit practical applications. Most biomarkers of interest are transported paracellularly into excreted biofluids from biomarker-rich blood and interstitial fluid during normal modulation of cellular tight junctions. Calcium chelators are reversible tight junction modulators that have been shown to increase absorption across the intestinal epithelium. However, calcium chelators have not yet been shown to improve the extraction of biomarkers. Here we show that for glucose, a paracellularly transported biomarker, the flux into sweat can be increased by >10x using citrate, a calcium chelator, in combination with electroosmosis. Our results demonstrate a method of increasing glucose flux through the sweat gland epithelium, thereby increasing the concentration in sweat. Future work should examine if this method enhances flux for other paracellularly transported biomarkers to make it possible to detect more biomarkers with currently available biosensors.

Evaluating the Transport Kinetics of a Model Compound Released From Cellulosic Coacervate Compositions Into Artificial Sebum

Complex coacervates of cationic polymers and anionic surfactants, which are produced spontaneously during the use of rinse-off formulations, represent an important delivery vehicle for topical agents to the skin surface and appendages. In this study, an artificial sebum-loaded cell culture insert method for determining the sebum diffusion properties of topical agents was optimized for in vitro release testing. This method was subsequently used to evaluate the transport kinetics of a model compound, kinetin, released from semi-solid coacervate formulations into sebum. Coacervate compositions were prepared with cationic-hydroxyethyl cellulose dodecyl sulfate (cat-HECDS), sodium dodecyl sulfate (NaDS), and water. Tested compositions ranged from 90 to 50 wt% water and had a cat-HECDS to NaDS wt% ratio of 2:1, 1:1, or 1:2, mimicking the in vivo hydration range and relative excess surfactant content expected from commercial rinse-off formulations. Steady-state flux of the model compound from each coacervate composition was found to vary with water content of the composition. When flux was plotted versus [(cat-HECDS:NaDS) × (1 - weight fraction water)]^-1, a strong linear correlation (R² = 0.89) emerged. The in vitro release testing method proved capable of discriminating between clinically relevant differences in transport kinetics from different coacervate formulations using a practical sample size.

Occurrence of organophosphorus flame retardants on skin wipes: Insight into human exposure from dermal absorption

This study surveyed occurrences and influencing factors of organophosphorus flame retardants (PFRs) on skin surface. Skin wipe samples from palms, back-of-hands and forearms of 30 adults were collected by using gauze pads soaked in isopropyl alcohol in Beijing, China. Tris(chloropropyl) phosphate isomers (∑TCPP), tris(2-chloroethyl) phosphate (TCEP) and triphenyl phosphate (TPHP) were the most abundant compounds with detection frequencies higher than 97%. ∑TCPP showed the highest mean level (4.6μg/m²), followed by TPHP (2.4μg/m²) and TCEP (1.6μg/m²). Levels on palms were slightly higher than on back-of-hands, and both were substantially higher than those on forearms. TCEP and ∑TCPP levels were strong reliable in three repeated measurements from 4 participants over a three month period (intraclass correlation of coefficient of 0.91 and 0.95, respectively), while TPHP levels were not. Washing with soap and water removed a large fraction of PFRs on hands with median reduction of 76, 72 and 67% for TCEP, ∑TCPP and TPHP, respectively. Paired dust samples, table surface wipe and hand wipe samples were collected from 17 offices (13 surface wipes and 22 hand wipes) in Beijing. Hand wipe TCEP, ∑TCPP and TPHP were neither correlated with dust samples nor with table surface wipe samples. Two methods were used for dermal exposure assessments. The estimated lower median total exposure from palms, back-of-hands and forearms by the relative absorption method were 0.6, 1.0, 0.3ng/kg BW-d for TCEP, ∑TCPP and TPHP, respectively. These estimates were in the same range as those via dust ingestion for adults in Beijing, suggesting dermal absorption is likely a significant pathway of human PFR exposure.

Measurement of morphological and physiological skin properties in aged care residents: a test-retest reliability pilot study

This test-retest pilot study investigated the intra-rater reliability and reproducibility of non-invasive technologies to objectively quantify morphological (colour, thickness and elasticity) and physiological (transepidermal water loss (TEWL), hydration, sebum and pH) skin properties in an aged care population. Three consecutive measurements were taken from five anatomical skin sites, with the mean of each measurement calculated. The intra-class correlation coefficient (ICC) and the standard error of measurement (SEM) were used to examine the intra-rater reliability and reproducibility of measurements. Non-invasive technologies in this study showed almost perfect reliability for ultrasound measurements of the subepidermal low echogenicity band (SLEB) (ρ = 0·95-0·99) and skin thickness (ρ = 0·95-0·99) across all sites. The ICC was substantial to almost perfect for pH (ρ = 0·76-0·88) and viscoelasticity (ρ = 0·67-0·91) across all sites. Hydration (ρ = 0·53-0·85) and skin retraction (ρ = 0·57-0·99) measurements ranged from moderate to almost perfect across all sites. TEWL and elasticity were substantial to almost perfect across four sites. Casual sebum levels and most colour parameters showed poor ICC. The use of non-invasive technologies in this study provided an objective and reliable means for quantifying ageing skin and may offer future studies a valuable option for assessing skin tear risk.

Influence of artificial sebum on the dermal absorption of chemicals in excised human skin: A proof-of-concept study

In an initial diffusion cell study, the influence of artificial sebum on dermal penetration and intradermal reservoir of ethanol and toluene was investigated in comparison with the effects of a skin cream (o/w- and w/o-emulsion) and untreated (control) skin. Human skin was exposed to neat ethanol and toluene for 4h, respectively. During the experiments, the penetration of the compounds was assessed in the receptor fluid. The amounts of the test compounds in the skin were determined at the end of exposure. In the control experiments, 42% of the total resorbed ethanol amounts were found in the intradermal reservoir after 4h, whereas 82% of the toluene amounts were found in the skin compartments. The treatment with artificial sebum showed no significant differences in dermal absorption of both test compounds compared to control skin. In contrast, the treatment with skin cream increased the percutaneous penetration (p<0.001) and the intradermal reservoir of ethanol ~2-fold but not of toluene. In all exposure scenarios, a relevant intradermal reservoir was formed. The results indicate that sebum does not influence the percutaneous penetration and the intradermal reservoir of epidermally applied chemicals, whereas the application of skin creams may increase the dermal penetration of the compounds.

Seborrheic Dermatitis and Dandruff: A Comprehensive Review

Seborrheic Dermatitis (SD) and dandruff are of a continuous spectrum of the same disease that affects the seborrheic areas of the body. Dandruff is restricted to the scalp, and involves itchy, flaking skin without visible inflammation. SD can affect the scalp as well as other seborrheic areas, and involves itchy and flaking or scaling skin, inflammation and pruritus. Various intrinsic and environmental factors, such as sebaceous secretions, skin surface fungal colonization, individual susceptibility, and interactions between these factors, all contribute to the pathogenesis of SD and dandruff. In this review, we summarize the current knowledge on SD and dandruff, including epidemiology, burden of disease, clinical presentations and diagnosis, treatment, genetic studies in humans and animal models, and predisposing factors. Genetic and biochemical studies and investigations in animal models provide further insight on the pathophysiology and strategies for better treatment.

Human sebum extract induces barrier disruption and cytokine expression in murine epidermis

BACKGROUND

Previous studies have shown that human sebum may play a role in barrier function but with much debate.

OBJECTIVE

To elucidate the effects of human sebum on skin barrier function.

METHODS

We used hairless mouse skin to study the functional and morphological alternation of epidermis after the application of human sebum.

RESULTS

The results showed a significant increase in transepidermal water loss and erythema value, and a decrease in skin hydration, accompanied by epidermal hyperplasia with parakeratosis following sebum application. Nile red staining together with electron microscopic examination confirmed the underlying mechanisms for sebum-induced barrier disruption are related directly to the interaction of sebum with the intracellular lipid lamellae of the SC, thereby leading to the increase in the fluidity of SC intracellular lipids as demonstrated by ATR-FTIR measurement. An inflammatory reaction characterized by an enhanced cytokine cascade, including up-regulation of TNF-α, IL-1α and IL-6, was also observed. On the other hand, there were insignificant expression of thymic stromal lymphopoietin and unchanged serum levels of IgE, suggesting non-immunogenic stimulation by sebum treatment.

CONCLUSION

It may be concluded that inflammation induced by excess amount of sebum is more likely an irritant contact dermatitis rather than an allergic one. Moreover, these findings implicated possible relationships between sebum, irritant contact dermatitis, and seborrheic dermatitis.

Oily skin: an overview

Oily skin (seborrhea) is a common cosmetic problem that occurs when oversized sebaceous glands produce excessive amounts of sebum giving the appearance of shiny and greasy skin. This paper overviews the main concepts of sebaceous gland anatomy and physiology, including the biosynthesis, storage and release of sebum, as well as its relationship to skin hydration and water barrier function. We also address how skin oiliness may vary according to diet, age, gender, ethnicity and hot humid climates. The deeper understanding of this skin type provides the opportunity to better guide patients regarding skin care and also assist in the development of sebosuppressive agents.

Stratum corneum dysfunction in dandruff

Synopsis

Dandruff is characterized by a flaky, pruritic scalp and affects up to half the world’s population post-puberty. The aetiology of dandruff is multifactorial, influenced by Malassezia, sebum production and individual susceptibility. The commensal yeast Malassezia is a strong contributory factor to dandruff formation, but the presence of Malassezia on healthy scalps indicates that Malassezia alone is not a sufficient cause. A healthy stratum corneum (SC) forms a protective barrier to prevent water loss and maintain hydration of the scalp. It also protects against external insults such as microorganisms, including Malassezia, and toxic materials. Severe or chronic barrier damage can impair proper hydration, leading to atypical epidermal proliferation, keratinocyte differentiation and SC maturation, which may underlie some dandruff symptoms. The depleted and disorganized structural lipids of the dandruff SC are consistent with the weakened barrier indicated by elevated transepidermal water loss. Further evidence of a weakened barrier in dandruff includes subclinical inflammation and higher susceptibility to topical irritants. We are proposing that disruption of the SC of the scalp may facilitate dandruff generation, in part by affecting susceptibility to metabolites from Malassezia. Treatment of dandruff with cosmetic products to directly improve SC integrity while providing effective antifungal activity may thus be beneficial.

Résumé

Les pellicules se caractérisent par un cuir chevelu prurigineux, squameux, et affectent jusqu’à la moitié de la population post-pubertaire du monde. L’étiologie des pellicules est multifactorielle, influencée par Malassezia, par la production de sébum, et par la susceptibilité individuelle. La levure commensale Malassezia est un facteur fortement contributif à la formation de pellicules, mais la présence de Malassezia aussi sur les cuirs chevelus sains indique que Malassezia seule n’est pas une cause suffisante. Un stratum corneum (SC) sain forme une barrière protectrice pour empêcher la perte d’eau et maintenir l’hydratation du cuir chevelu. Il protège également contre les agressions externes tels les micro-organismes, y compris Malassezia, ou des substances toxiques. Des dommages aigus ou chroniques au niveau de la barrière peuvent nuire à une bonne hydratation, conduisant à des effets atypiques de la prolifération épidermique, de la différenciation des kératinocytes, et de la maturation du SC, ce qui peut expliquer une partie des symptômes des pellicules. L’appauvrissement et la désorganisation des lipides structurels d’un stratum corneum sujet aux pellicules sont compatibles avec la notion d’une barrière affaiblie telle qu’indiquée par une perte d’eau transépidermique élevée. Une preuve supplémentaire d’une barrière affaiblie dans les cas des pellicules est fournie par un niveau d’inflammation infraclinique et une plus grande susceptibilité aux irritants topiques. Nous proposons que la perturbation du SC du cuir chevelu facilite la production de pellicules, en partie en augmentant la sensibilité aux métabolites de Malassezia. Le traitement des pellicules avec des produits cosmétiques pour améliorer directement l’intégrité du SC, tout en offrant une activité antifongique efficace peut donc être bénéfique.

Distinct locational differences observable in biophysical functions of the facial skin: with special emphasis on the poor functional properties of the stratum corneum of the perioral region

The face is composed of complicated anatomical components, presenting unique portions, such as the eyes, nose and mouth in a relatively narrow area. Moreover, the facial skin is densely populated by the pilosebaceous units and sweat glands, and its stratum corneum (SC) is much thinner than that of the trunk and limbs, although it is always exposed to the environment. Among various portions of the facial skin, some are more easily irritated than others by environmental stimuli, or are more often affected by certain dermatoses. However, the functional aspects of the different portions of the facial skin have not been studied in detail under a strictly controlled environment in sufficiently large numbers of subjects covering different age groups. Thus, we conducted studies in winter with various biophysical techniques, such as transepidermal water loss (TEWL), as a parameter for SC barrier function, high-frequency conductance as that for skin surface hydration state, skin surface lipids, pH, blood flow and skin surface temperature on the forehead, mid-portion of the cheek (cheek in short), nasal tip (nose in short), nasolabial fold and chin of 20 healthy Japanese females aged 22-37 years (average 25 years) in a climate chamber adjusted to 21 degrees C and 50% relative humidity. Thereafter, we studied the influence of ageing on these biophysical parameters by collecting data of TEWL, high-frequency conductance and size of superficial corneocytes on the cheek, nasolabial fold and chin of 303 healthy Japanese female volunteers of different ages. The obtained results showed that the barrier function of the SC was best on the cheek, presenting the lowest TEWL, which was significantly higher on the nasolabial fold and chin than on the cheek. TEWL showed a decrease with age. In contrast, skin hydration state was higher on the nose, but it tended to be lower on the nasolabial fold, showing a mild age-related increase. The corneocytes on the nasolabial fold and chin were smaller than those on the cheek. They revealed a clear increase in size with age. Skin surface lipids were richest on the nose, whereas the superficial pH on the nose was the lowest among the regions tested. The skin temperature was lowest on the cheek than on other areas of the face; although, together with the nose, its blood flow was higher than that of the others. These data indicate great regional differences observable in SC functions on the face. In general, the SC barrier function increases with age, probably because of a decreased epidermal turnover rate as recognized by the increase in corneocyte size. Among the various sites, the skin of the nasolabial fold and chin, whose SC consisted of the smallest corneocytes, showed poorest SC properties in barrier function, suggesting the presence of mild invisible inflammation. It is understandable that this area easily develops not only the complaint of sensitive skin to cosmetics but also dermatitis because of various external agents.

The secretion of areolar (Montgomery's) glands from lactating women elicits selective, unconditional responses in neonates

BACKGROUND

The communicative meaning of human areolae for newborn infants was examined here in directly exposing 3-day old neonates to the secretion from the areolar glands of Montgomery donated by non related, non familiar lactating women.

METHODOLOGY/PRINCIPAL FINDINGS

The effect of the areolar stimulus on the infants' behavior and autonomic nervous system was compared to that of seven reference stimuli originating either from human or non human mammalian sources, or from an arbitrarily-chosen artificial odorant. The odor of the native areolar secretion intensified more than all other stimuli the infants' inspiratory activity and appetitive oral responses. These responses appeared to develop independently from direct experience with the breast or milk.

CONCLUSION/SIGNIFICANCE

Areolar secretions from lactating women are especially salient to human newborns. Volatile compounds carried in these substrates are thus in a position to play a key role in establishing behavioral and physiological processes pertaining to milk transfer and production, and, hence, to survival and to the early engagement of attachment and bonding.

The effect of 2% niacinamide on facial sebum production

BACKGROUND

The presence of sebum on the face is responsible for both facial shine and the formation of comedonal and inflammatory acne lesions. Sebum control is a goal of many OTC skin care products; however, most currently available products function by absorbing sebum from the face rather than modulating its production.

OBJECTIVE

To demonstrate the effect of topical 2% niacinamide on sebum excretion rates and casual sebum production in Oriental and Caucasian populations.

METHODS

Separate clinical trials were conducted in both Japan and the USA to evaluate the effect of topical 2% niacinamide in different ethnic groups. A total of 100 Japanese subjects were enrolled in a double-blind, placebo-controlled comparison between two independent balanced groups. Fifty subjects applied the 2% niacinamide moisturizer to the face for 4 weeks and 50 subjects used a placebo moisturizer for 4 weeks, with sebum excretion rate (SER) measurements taken at baseline, week 2, and week 4. In addition, 30 Caucasian subjects were enrolled in a randomized split-face study for 6 weeks with SER and casual sebum levels (CSL) measured at baseline, week 3, and week 6.

RESULTS

The results of the Japanese study demonstrated that the SER of the two groups was not significantly different at baseline, but the 2% niacinamide treated group demonstrated significantly lowered SER after 2 and 4 weeks of application. The results were somewhat different in the Caucasian study. After 6 weeks of treatment, the CSL was significantly reduced, but the SER was not significantly reduced.

CONCLUSIONS

Topical 2% niacinamide may be effective in lowering the SER in Japanese individuals and CSL in Caucasian individuals.

Textiles and Human Skin, Microclimate, Cutaneous Reactions: An Overview

This article overviews research in the interdisciplinary area of textile/skin interaction and related cutaneous intolerance. Microclimate in the skin/clothing system and especially the skin responses relates to the moisture and heat transfer within this system and plays a critical role in skin irritation from textiles. A discussion is then given on skin irritation reactions to textiles, including intolerance caused by chemicals (dyes and finishes) and physical contact/friction. Finally, two skin injuries, blisters and pressure ulcers, which are caused by physical contact, pressure, and friction, are documented. Despite the prevalent problems caused by ill textile/skin interactions, minimal efforts have been devoted to this field. In addition, the in vivo experimental studies infrequently lead to a solid conclusion. The cause may lie in the dramatic variation of skin conditions among individuals as well as among different anatomic sites of the same person. Another reason might be the lack of communications between researchers in the areas of textiles and dermatology.

Dissolution of materials in artificial skin surface film liquids

The dissolution of chemical constituents from jewelry, textiles, cosmetics, drugs, industrial chemicals, and particles in direct and prolonged contact with human skin is often assessed in vitro using artificial skin surface film liquids (SSFL). To provide meaningful results, the composition of artificial SSFL should accurately mimic human sweat and sebum, and the conditions of the in vitro test system should accurately reflect in vivo skin conditions. We summarized the reported composition of human SSFL and compared it to 45 different formulations of artificial sweat and 18 formulations of artificial sebum (studies published from 1940 to 2005). Conditions of in vitro dissolution test systems were reviewed and compared to in vivo skin conditions. The concentrations of individual constituents and pH of artificial sweat and concentrations of artificial sebum constituents are not always within ranges reported for human SSFL. Nearly all artificial SSFL lack many of the constituents in human SSFL. To develop a comprehensive model SSFL, we propose a standard SSFL, modified from the two best published sweat and sebum formulations. Little is known concerning the influence of test system conditions on dissolution, including SSFL temperature, container material composition, agitation, and physicochemical properties of the test article on dissolution. Thus, both a need and an opportunity exist for standardizing the composition of artificial SSFL and in vitro dissolution test methodologies. To standardize in vitro dissolution test systems, we recommend: maintaining artificial SSFL at a biologically relevant temperature appropriate to the human activity being modeled, carefully selecting test and sample storage containers to avoid bias in dissolution measurements, accounting for friction between a test article and skin in a biologically plausible manner, and physicochemical characterization of the test article or material to better understand mechanisms of dissolution and potential mechanisms of toxic action of dissolved material. More accurate modeling and better understanding of chemical dissolution from articles in contact with the skin will ultimately improve risk decision making, thereby protecting even the most susceptible persons from adverse health effects resulting from skin exposure.

Topical exposure to carbon disulfide induces epidermal permeability alterations in physiological and pathological changes

Carbon disulfide (CS2) has been suggested its possible skin toxicity. Neither a dose-response relationship nor any mechanism of CS2-exposure regarding epidermal permeability alterations has been postulated. The objectives of this study were to evaluate the dose-dependent association and the pathological changes with CS2 topically applied to mouse epidermis. Four concentrations of CS2 (0% (controls), 10%, 15%, and 20% in ethanol) were topically applied to a 1.8 cm2 area of the lateral abdomen of female nude mice for 10 min. Time-series transepidermal water loss (TEWL) profile, morphological examinations by both light microscopy (hematoxylin/eosin stain and Nile Red stain) and electronic microscopy, and lipid analysis by high performance thin-layer chromatography (HPTLC) were used to evaluate the epidermal impairment. We found no recovery occurred within 72 h exposure to 20% CS2 in contrast to substantial recovery found in 10% and 15% CS2-exposure. Clear dose-dependent fashions were shown in TEWL elevations, recovery retardation, and lipid extraction across the ethanol (control), 10%, 15%, and 20% CS2 exposures. Two mechanistic pathways were raised to account for CS2-induced epidermal alterations: intercellular lipid depletion and keratinocyte damage. A study with different test animal species is warranted owing to the discrepancies in epidermis between nude mice and other species.

Loss of keratin 10 is accompanied by increased sebocyte proliferation and differentiation

Here, we present strong evidence that the targeted deletion of keratin 10 (K10) alters sebocyte differentiation in mice, mediated by an increased proliferation and differentiation of cells located in the periphery of the glands. This was not accompanied by the induction of the proliferation-associated keratins K6, K16 and K17. Sebaceous gland cells of K10-/- mice showed an accelerated turnover and secreted more sebum including wax esters, triglycerides, and cholesterol esters. The levels of the major epidermal lipids ceramides and cholesterol were also increased, whereas glycosylceramides and sphingomyelin were decreased which was not based on altered sphingolipid biosynthesis. The amount of Cer(OS), covalently bound to the cornified envelope, remained unchanged, as well as the amount of loricrin and involucrin. In agreement with the unaltered expression of beta-catenin and its targets cyclin D1 and c-Myc, we conclude that the altered composition of the suprabasal intermediate filament cytoskeleton in K10-/- mice increased the differentiation of epidermal stem cells towards the sebocyte lineage.

Influence of the hydrophobic and hydrophilic characteristics of sliding and slider surfaces on friction coefficient: in vivo human skin friction comparison

INTRODUCTION

The objective of this study was to investigate whether hydrophilic/hydrophobic balance (Hi/Ho) of the skin surface strongly modifies the friction coefficient (mu). The Hi/Ho balance is determined using the relationship between the critical surface tension gammac (Zisman's principle:which delimits the wetting capacity) and the surface tension of water gammaH2O (water: reference element of Hi/Ho balance).

METHOD

Critical surface tension gammac was determined (according to Zisman's principle) through the measurement of advancing contact angle theta of a series of ethanol/water dilutions. Friction coefficient depends on several parameters: types of probe motions (rotational vs. linear), surface roughness and physicochemical parameters of surfaces in contact). In this study, the wettability parameters for six surfaces (human skin forearm, Teflon, silicone impression material 'Silflo', vinyl polysiloxane impression material 'resin' steel and glass) were measured and their influences were compared to friction coefficient mu.

RESULTS

This study shows that the higher hydrophobia tendency of the surfaces, the lower friction coefficient. The use of three sliding materials (Teflon, steel and glass) of different Hi/Ho balance confirms the importance of these physicochemical parameters in mu. For example, Teflon with high hydrophobia has a low mu. Friction coefficient increased when hydrophobia of sliding and slider surfaces decreased.

CONCLUSION

Friction coefficient value depends on the type of slider surface and its physicochemical properties. In vivo,the friction coefficient may quantify the influence of lubrificant/emolients/moisturizers. For example, the friction coefficient of hydrated skin (through the action of moisturizing products) is higher than the friction coefficient of dry skin. The relationship between the friction coefficient and the Hi/Ho balance can be reversed in the presence of water and sebum on forehead, for example.

Glycerol regulates stratum corneum hydration in sebaceous gland deficient (asebia) mice

The only known function of human sebaceous glands is the provocation of acne. We assessed here whether sebum influences stratum corneum hydration or permeability barrier function in asebia J1 and 2 J mice, with profound sebaceous gland hypoplasia. Asebia J1 mice showed normal permeability barrier homeostasis and extracellular lamellar membrane structures, but they displayed epidermal hyperplasia, inflammation, and decreased (>50%) stratum corneum hydration, associated with a reduction in sebaceous gland lipids (wax diesters/monoesters, sterol esters). The triglyceride content of both asebia and control stratum corneum was low, consistent with high rates of triglyceride hydrolysis within the normal pilosebaceous apparatus, despite high rates of triglyceride synthesis. Although a mixture of synthetic, sebum-like lipids (sterol/wax esters, triglycerides) did not restore normal stratum corneum hydration to asebia skin, topical glycerol, the putative product of triglyceride hydrolysis in sebaceous glands, normalized stratum corneum hydration, and the glycerol content of asebia stratum corneum was 85% lower than in normal stratum corneum. In contrast, another potent endogenous humectant (urea) did not correct the abnormality. The importance of glycerol generation from triglyceride in sebaceous glands for stratum corneum hydration was demonstrated further by (i) the absence of sebaceous-gland-associated lipase activity in asebia mice, whereas abundant enzyme activity was present in the glands of control mice; and (ii) the inability of high concentrations of topical triglyceride to correct the hydration abnormality, despite the presence of abundant lipase activity in asebia stratum corneum. These results show that sebaceous-gland-derived glycerol is a major contributor to stratum corneum hydration.

Noninvasive characterization of regional variation in drug transport into human stratum corneum in vivo

PURPOSE

To investigate the mechanisms underlying the regional variations in drug transport into human stratum corneum (SC) of two model compounds of different lipophilicity and molecular size, 4-cyanophenol (CP) and cimetidine (CM), in vivo by non-invasive, quantitative attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy.

METHODS

Saturated solutions of CP and CM were applied to the skin surface of eleven Chinese men, at five anatomical sites, including forearm, back, thigh, leg, and abdomen, for 10-15 min and 3-5 h, respectively. After the skin surface was cleansed of remaining chemicals, the SC was tape-stripped sequentially up to 20 times, and the drug concentration profiles in the tape-stripped SC were determined using ATR-FTIR spectroscopy. Thickness of the SC was estimated simultaneously using two-point measurements of transepidermal water loss before and after completion of tape stripping. Estimation of partition, diffusion, and permeability coefficients was achieved by analysis of the data using the unsteady-state diffusion equation.

RESULTS

The rank orders of regional variation in partition and diffusion coefficients of CP and CM were different. The rank order of regional variation in permeability coefficients was similar for both drugs and decreased in the order of back > forearm > thigh > leg > or = abdomen, but the variation was more prominent for CM.

CONCLUSIONS

Regional variation in SC transport of CP was mainly influenced by its intrinsic diffusivity across the SC, whereas variation in transport of CM could be attributed to both thermodynamic and kinetic differences among different anatomical skin sites.

Epidermal barrier lipids in human vernix caseosa: corresponding ceramide pattern in vernix and fetal skin

BACKGROUND

Vernix caseosa is a protective biofilm covering the fetus during the last trimester. Vernix and epidermal barrier lipids (i.e. cholesterol, free fatty acids and ceramides) appear to share protective functions for fetal and neonatal skin.

OBJECTIVES

To analyse vernix samples for epidermal barrier lipid content, and to compare lipid profiles of vernix with those of fetal and postnatal epidermis.

METHODS

Vernix samples were collected from 21 healthy term neonates. Skin samples were collected from 10 fetuses aborted between gestational week (GW) 16 and 25, nine infants and 11 older children. Lipids were extracted according to standard protocols and analysed by high-performance thin-layer chromatography.

RESULTS

Vernix contained 196.5 +/- 70.1 microg barrier lipids mg-1 protein (mean +/- SD). Cholesterol formed the major barrier lipid fraction (52.8%), followed by free fatty acids (27.7%) and ceramides (20.1%). The ceramide composition of vernix resembled that of mid-gestational (GW 23-25) fetal epidermis both qualitatively and quantitatively, while there were major differences from postnatal epidermis. The total epidermal ceramide concentration increased significantly between prenatal and postnatal samples.

CONCLUSIONS

The composition pattern of ceramides mirrors that of mid-gestational fetal epidermis. Vernix thus represents a 'homologous' substitute for the immature epidermal barrier in fetal skin. The differential role of individual ceramides in this process remains to be established.

Aberrant lipid organization in stratum corneum of patients with atopic dermatitis and lamellar ichthyosis

There are several skin diseases in which the lipid composition in the intercellular matrix of the stratum corneum is different from that of healthy human skin. It has been shown that patients suffering from atopic dermatitis have a reduced ceramide content in the stratum corneum, whereas in the stratum corneum of lamellar ichthyosis patients, the amount of free fatty acids is decreased and the ceramide profile is altered. Both patient groups also show elevated levels of transepidermal water loss indicative of an impaired barrier function. As ceramides and free fatty acids are essential for a proper barrier function, we hypothesized that changes in the composition of these lipids would be reflected in the lipid organization in stratum corneum of atopic dermatitis and lamellar ichthyosis patients. We investigated the lateral lipid packing using electron diffraction and the lamellar organization using freeze fracture electron microscopy. In atopic dermatitis stratum corneum, we found that, in comparison with healthy stratum corneum, the presence of the hexagonal lattice (gel phase) is increased with respect to the orthorhombic packing (crystalline phase). In lamellar ichthyosis stratum corneum, the hexagonal packing was predominantly present, whereas the orthorhombic packing was observed only occasionally. This is in good agreement with studies on stratum corneum lipid models that show that the presence of long-chain free fatty acids is involved in the formation of the orthorhombic packing. The results of this study also suggest that the ceramide composition is important for the lateral lipid packing. Finally, using freeze fracture electron microscopy, changes in the lamellar organization in stratum corneum of both patient groups could be observed.

Effect of barrier disruption by acetone treatment on the permeability of compounds with various lipophilicities: implications for the permeability of compromised skin

The permeability of compromised skin barrier was investigated in vitro using acetone-disrupted hairless mouse skin as a model membrane. The effect of compound lipophilicity was studied using sucrose, caffeine, hydrocortisone, estradiol, and progesterone as model compounds. The results demonstrated that permeability barrier disruption by acetone treatment significantly enhanced the permeability of the skin to both hydrophilic and amphipathic compounds, including sucrose, caffeine and hydrocortisone. This effect was more prominent with caffeine and hydrocortisone at different transepidermal water loss (TEWL) levels. Acetone treatment, however, didn't appear to alter the percutaneous penetration of highly lipophilic compounds, such as estradiol and progesterone. The characteristics of skin permeability were described by parabolic relationships between log P(WS) (permeability coefficient of whole skin) and log K(O/W) (octanol/water partition coefficient) at different degrees of permeability barrier disruption. The optimal log K(O/W) of compounds for skin penetration appeared to decrease with an increase in TEWL levels. The maximal permeability achieved was similar through skin displaying different TEWL levels. In an attempt to explore the underlying mechanisms for the changes in skin permeability, the stratum corneum/normal saline partition coefficients of water, caffeine, and hydrocortisone either decreased or remained unaffected with an increase in TEWL. Electron microscopic examinations have revealed reductions in stratum corneum lipid content and alterations in intercellular membrane structures as a result of acetone treatment, whereas negligible changes in the number of horny layers were observed by safranin staining of the stratum corneum. We have concluded that the enhancement in skin permeability to both hydrophilic and amphipathic compounds by acetone treatment arose mainly because of the increase in stratum corneum diffusivity at higher TEWL levels. The results imply the possibility of using both TEWL and drug lipophilicity to predict alterations in skin permeability and hence the dose adjustment of topically applied medication for patients with impaired skin barrier function.

The influence of two azones and sebaceous lipids on the lateral organization of lipids isolated from human stratum corneum

The main problem with topical application of compounds to administer drugs to and regulate drug levels in a human body, is the barrier formed by the intercellular lipid matrix of the stratum corneum (SC). In a search for possibilities to overcome this barrier function, a good understanding of the organization and phase behavior of these lipids is required. SC lipid model studies especially provide a wealth of information with respect to the lipid organization and the importance of certain subclasses of lipids for the structure. Previously, we have shown that electron diffraction (ED) provides detailed information on the lateral lipid packing in both intact SC (G.S.K. Pilgram et al., J. Invest. Dermatol. 113 (1999) 403) and SC lipid models (G.S.K. Pilgram et al., J. Lipid Res. 39 (1998) 1669). In the present study, we used ED to examine the influence of two azones and sebaceous lipids on the lateral phase behavior of lipids isolated from human SC. We established that human SC lipids are arranged in an orthorhombic packing pattern. Upon mixing with the two enhancers the orthorhombic packing pattern was still observed; however, an additional fluid phase became more apparent. In mixtures with sebaceous lipids, the presence of the hexagonal lattice increased. These findings provide a basis for the mechanism by which these enhancers and sebaceous lipids interact with human SC lipids.

Characterization of vernix caseosa: water content, morphology, and elemental analysis

Recent studies have prompted interest in the use of epidermal barrier creams as protective biofilms for very low birthweight preterm infants. The key to understanding the role of epidermal barrier films is an elucidation of their interaction with water and a basic knowledge of their composition. In this study, we investigated the morphologic properties and elemental composition of the naturally occurring biofilm, vernix caseosa. This biofilm is typically lacking in preterm infants and its production coincides in utero with terminal differentiation of the epidermis and formation of the stratum corneum. Significantly, vernix (80.5+/-1.0% H2O) had a much higher water content than other barrier creams (Eucerin: 17.1+/-0.6%, Aquaphor: 0.33+/-0.03%, Ilex: 0.19+/-0.02%, petrolatum: 0.03+/-0.01%; all p<0.05). Phase contrast microscopy of vernix showed multiple cellular elements with nucleic "ghosts" embedded in a putative lipid matrix. Transmission electron microscopy revealed flattened structures approximately 1-2 microm in thickness with distinct cellular envelopes indicative of differentiated corneocytes. Compared with mature corneocytes in adult stratum corneum, vernix corneocytes appeared swollen, the density of the keratin filaments was less, and there was a relative lack of tonofilament orientation. Cryofractured specimens were examined by cryoscanning electron microscopy with subsequent elemental localization by X-ray beam analysis. The findings indicate the high water content of vernix is largely compartmentalized within fetal corneocytes. These results are consistent with the novel view of vernix as a "fluid phase" stratum corneum consisting of a hydrophobic lipid matrix with embedded fetal corneocytes possessing unique biomechanical and water-binding properties.

The effect of two azones on the lateral lipid organization of human stratum corneum and its permeability

PURPOSE

Investigation of the relationship between changes in human SC lipid organization induced by N-alkyl-azocycloheptane-2-one and SC permeability to the model compound HgCl2.

METHODS

Human dermatomed skin was treated with propylene glycol (PG), oleyl-Azone (OAz) or dodecyl-Azone (DAz) in 0.15 M PG. Untreated skin served as control. The lateral lipid organization was studied by electron diffraction. Hg was measured on tape-strips by X-ray microanalysis and in the acceptor phase by atom absorption spectrometry.

RESULTS

In control and PG treated samples, the lipid packing was mainly orthorhombic, while a small fraction was hexagonal. In OAz and DAz treated samples, the orthorhombic lipid organization remained, however, the hexagonal packing was recorded less frequently. The amount of Hg decreased as a function of depth in all SC samples, however, the penetration profile increased significantly upon OAz treatment. The cumulative amount of Hg in the acceptor phase of OAz treated samples also increased significantly compared to control and PG treated samples.

CONCLUSIONS

The increased penetration of Hg into OAz treated skin could not be related to an orthorhombic-hexagonal phase transition. Alternatively, phase separation of OAz and/or formation of grain boundaries might affect SC permeability, hereby increasing Hg penetration. A similar mechanism is proposed for DAz.