K. De Paepe

A keratinocyte's course of life.

An adequate permeability barrier function of the mammalian epidermis is guaranteed by the characteristic architecture of the stratum corneum. This uppermost layer consists of a highly organized extracellular lipid compartment which is tightly joined to the corneocytes. The generation of the extracellular lipid compartment and the transformation of the keratinocytes into corneocytes are the main features of epidermal differentiation. However, equally important is the continuous renewal of the stratum corneum, which is insured by a careful balance between the replenishment of new keratinocytes from the proliferating basal layer, and the well-orchestrated loss of the most superficial cells after the so-called ‘epidermal programmed cell death’. In this overview, the complete life of keratinocytes is described, from the proliferative organization to the process of desquamation.

Microrelief of the skin using a light transmission method

Abstract The recently developed Skin Visiometer, based on light transmission through blue-coloured silicone replicas, was used to study skin microrelief. Calibrated metal plates displaying lines with depths between 6 and 361 μm, were used to determine the accuracy, sensitivity and reproducibility of the technique as well as the parameters of importance during measurement. The precision of the measurements was particularly good between 10 μm and 361 μm. The sensitivity of the method was between 10 and 20 μm. Replicas of volar forearm skin were taken from four groups ( n = 15) of male and female volunteers in the age ranges 20 to ¶30 years and 55 to 65 years. In addition to the instrumental roughness parameters (Rz, Rt, Rm and Ra), the surface of the furrows, the number of primary and secondary lines and the number of intersections were determined. For both sexes, significantly lower values were observed for Rz, Rm and Rt in the younger age group than in the older age group. In addition, the numbers of primary and secondary lines and the number of intersections were higher, pointing to a more structured microrelief in younger forearm skin. Diurnal rhythm, the relative humidity of the measuring room and the position of the forearm were found to be significant factors, while room temperature and precleansing of the skin with mild products were not. Following the application of a hydrating cream (twice daily for 14 days) to the forearm skin of the older female age group, the Rz, Rt, Rm and Ra decreased, while the other parameters measured, except for the surface taken in by the lines, increased, indicating that the microrelief was modified towards the typical pattern observed in young skin.

Repair of acetone- and sodium lauryl sulphate-damaged human skin barrier function using topically applied emulsions containing barrier lipids

Background It is generally acknowledged that well‐formulated moisturizing skin care products can restore disturbed barrier function that can be assessed by transepidermal water loss (TEWL) measurements. When ceramides and/or other barrier lipids are incorporated, it is, however, not always clearly demonstrated which ingredients of the formulation exert the beneficial effects.

Characterization of suspected illegal skin whitening cosmetics.

An important group of suspected illegal cosmetics consists of skin bleaching products, which are usually applied to the skin of the face, hands and décolleté for local depigmentation of hyper pigmented regions or more importantly, for a generalized reduction of the skin tone. These cosmetic products are suspected to contain illegal active substances that may provoke as well local as systemic toxic effects, being the reason for their banning from the EU market. In that respect, illegal and restricted substances in cosmetics, known to have bleaching properties, are in particular hydroquinone, tretinoin and corticosteroids. From a legislative point of view, all cosmetic products containing a prohibited whitening agent are illegal and must be taken off the EU market. A newly developed screening method using ultra high performance liquid chromatography-time off flight-mass spectrometry allows routine analysis of suspected products. 163 suspected skin whitening cosmetics, collected by Belgian inspectors at high risk sites such as airports and so-called ethnic cosmetic shops, were analyzed and 59% were classified as illegal. The whitening agents mostly detected were clobetasol propionate and hydroquinone, which represent a serious health risk when repeatedly and abundantly applied to the skin.

Analysis of Epidermal Lipids of the Healthy Human Skin: Factors Affecting the Design of a Control Population

The intervariability of studies on the lipids of human epidermis and stratum corneum is high because of the different origin of the skin samples and the variety of extraction methods used. In the present work, a high-performance thin-layer chromatographic technique has been used to study the parameters age, sex, and anatomical site for their effects on the lipid profiles recovered from healthy epidermal skin biopsy specimens. It was found that sex-related differences were seen at the level of the total ceramide concentration. Observed decreases in lipid concentration, due to ageing, depended on the anatomical site. Therefore, these variables should be controlled in a reproducible and standardized way in order to be able to study the direct relationship between skin condition and barrier lipid composition. Only when this relation is established, results of topical treatment can be scientifically evaluated.

Epidermal ceramidase activity regulates epidermal desquamation via stratum corneum acidification.

The acidic pH of the outer surface of the mammalian skin plays several important roles in the epidermal barrier function. The 2 endogenous pathways that are currently known to elicit this acidic pH are the generation of free fatty acids from phospholipids and the exchange of protons for sodium ions by non-energy-dependent sodium-proton exchangers. In this study, we propose a third endogenous pathway, i.e. epidermal ceramidase activity, generating free fatty acids from ceramides. By topical application of N-oleylethanolamine, a well-known ceramidase inhibitor, we could demonstrate a significant increase in the stratum corneum pH and a corresponding decrease in the epidermal free fatty acid content. Moreover, we could show that the resulting change in the apparent skin pH also provoked a delay in early barrier recovery and an increased epidermal desquamation, corresponding to earlier observations made for the already known endogenous mechanisms.

HS–GC–MS method for the analysis of fragrance allergens in complex cosmetic matrices

Potential allergenic fragrances are part of the Cosmetic Regulation with labelling and concentration restrictions. This means that they have to be declared on the ingredients list, when their concentration exceeds the labelling limit of 10 ppm or 100 ppm for leave-on or rinse-off cosmetics, respectively. Labelling is important regarding consumer safety. In this way, sensitised people towards fragrances might select their products based on the ingredients list to prevent elicitation of an allergic reaction. It is therefore important to quantify potential allergenic ingredients in cosmetic products. An easy to perform liquid extraction was developed, combined with a new headspace GC-MS method. The latter was capable of analysing 24 volatile allergenic fragrances in complex cosmetic formulations, such as hydrophilic (O/W) and lipophilic (W/O) creams, lotions and gels. This method was successfully validated using the total error approach. The trueness deviations for all components were smaller than 8%, and the expectation tolerance limits did not exceed the acceptance limits of ± 20% at the labelling limit. The current methodology was used to analyse 18 cosmetic samples that were already identified as being illegal on the EU market for containing forbidden skin whitening substances. Our results showed that these cosmetic products also contained undeclared fragrances above the limit value for labelling, which imposes an additional health risk for the consumer.

Kinetic characteristics of acidic and alkaline ceramidase in human epidermis.

It has recently become evident that at least five ceramidase (CDase) isoforms are present in human epidermis, and that specifically acidic CDase (aCDase) and alkaline CDase (alkCDase) activities increase during keratinocyte differentiation, and thus might play a pivotal role(s) in permeability barrier function. Prior to investigating their possible roles in the epidermal barrier function, it is necessary to characterize basic kinetic parameters for these enzymes, as well as to determine the effects of the established CDase inhibitors and their activities. In this study, assays for both aCDase and alkCDase activities in fully differentiated human epidermis were optimized using a radiolabeled substrate. These studies revealed that aCDase activity is substantially higher than alkCDase activity, and that both isoenzymes are inhibited by a CDase inhibitor N-oleylethanolamine. These findings were also confirmed using an in situ enzyme assay.

Seasonal Effects on the Nasolabial Skin Condition

In the present work, nasolabial skin condition and the influence of seasonal changes during autumn and winter were studied in 16 healthy female volunteers. Apart from visual scoring of erythema and skin scaliness, transepidermal water loss (TEWL), skin hydration, apparent skin pH, skin colour and skin desquamation were biophysically measured. The study results showed that nasolabial TEWL was significantly higher during wintertime than in autumn. Also skin colour measurements and squamometry scorings revealed higher values, indicating a more reddish and scaly nasolabial skin during winter compared to autumn. Results from tape stripping and skin surface lipid analysis by high-performance thin-layer chromatography demonstrated significant differences for triglycerides and cholesterol esters, indicating a functionally inferior hydrolipidic layer during the winter season.

Overview of skin whitening agents with an insight into the illegal cosmetic market in Europe

Lightening skin tone is an ancient and well‐documented practice, and remains common practice among many cultures. Whitening agents such as corticosteroids, tretinoin and hydroquinone are medically applied to effectively lighten the skin tone of hyperpigmented lesions. However, when these agents are used cosmetically, they are associated with a variety of side‐effect. Alternative agents, such as arbutin and its derivatives kojic acid and nicotinamide have been subsequently developed for cosmetic purposes. Unfortunately, some cosmetics contain whitening agents that are banned for use in cosmetic products. This article provides an overview of the mode of action and potential side‐effects of cosmetic legal and illegal whitening agents, and the pattern of use of these types of products. Finally, an EU analysis of the health problems due to the presence of illegal products on the market is summarized.