Influence of skin extension upon the epidermal morphometry, an in vivo study.

BACKGROUND: The Dermal-Epidermal Junction (DEJ) is characterized by undulations whose apices are called papillae. With aging, epidermis becomes thinner, together with a flattening of the DEJ, leading to a decreased density of papillae. The causes of these modifications are likely as multiple as uncertain. The present paper deals with in vivo morphometric characterization of the DEJ and its changes following a skin surface deformation. METHODS: Living epidermis of human adults was examined by means of in vivo Reflectance Confocal Microscopy. Distances between skin surface and papillae apex and pegs of the DEJ were, respectively, recorded in both relaxed and stretched skin situation. The number of papillae present within a single image (field of view, 500 × 500 µm) was also measured. RESULTS: Skin extension has no effect upon the distance between skin surface and the apex of papillae. In contrast, the distance between skin surface and the pegs of papillae decreases. On the other hand, skin extension leads to a significant decrease in the number of papillae within a single image. CONCLUSION: Epidermal atrophy and structural changes observed in the DEJ with aging may be, by some extent, related to daily and repetitive skin deformations all along the life span.

Influence of Stratum Corneum on the entire skin mechanical properties, as predicted by a computational skin model.

BACKGROUND/PURPOSE: Skin mechanical properties are globally well described. The aim of this paper is to evaluate, by means of a numerical model, the influence of Stratum Corneum (SC) on skin folding resulting from an in-plane compression. METHODS: A computational skin model was developed where skin is divided into three layers (SC, epidermis and upper dermis, and deep dermis) of different thicknesses and elastic moduli. Skin surface deformation, consecutive to the application of a given surface compression, was computed by minimizing the mechanical energy of the multi-layered tissue. Influence of SC thickness and elastic modulus on skin buckling is presented. RESULTS: Varying both SC thickness and elastic modulus has a marked influence on both wavelength and amplitude of the skin's surface folds. These two parameters display a logarithmic variation versus SC elastic modulus. CONCLUSION: Although representing about one hundredth of the total skin thickness, SC has a marked influence on the skin mechanical properties.

Longitudinal study of skin aging: from microrelief to wrinkles.

AIM: To study the changes in skin microrelief and periocular wrinkles during the aging process. METHODS: Replicas of the crow's feet area of volunteers were recorded in 1987 and 2008 and observed comparatively. Characteristic features were quantified by image analysis. RESULTS: Observation shows that some microrelief features disappear and even merge with wrinkles that become more marked. Some primary lines also tend to merge to form thin new wrinkles. Quantitative data support these observations: the size of small and medium objects of skin relief decreases with age while large objects are becoming larger. CONCLUSION: Over 21 years, in the group studied, the total area of the detected objects remains quite constant. Only the distribution between small and large detected objects (microrelief features and wrinkles, respectively) is modified.

Photoaging of the chest analyzed by capacitance imaging.

OBJECTIVE: Capacitance imaging is a new technique using sensors based on silicon technology developed to record fingerprints for security reasons. Applying such a sensor onto the skin surface gives the capacitance (hydration) map of the skin surface with a two-dimensional resolution of 50 microm. This method was used to characterize skin of the chests of 64 women with various grades of skin photoaging. METHOD: The severity of photoaging of the chest skin of 64 women was clinically assessed according to a six-grade scale. Capacitance images of the skin were recorded and analyzed in terms of mean capacitance, homogeneity of gray levels and density of microrelief lines. Capacitance images of the adjacent unexposed area (upper part of the breast) were also recorded and analyzed for comparison. Pictures of the different areas were recorded. RESULTS: Microrelief line density decreases with the age of the volunteers but is independent of the severity of photoaging. Mean hydration of the skin surface is found to be independent of both photoaging severity and age. Evenness of hydration is a parameter markedly linked to the severity of photoaging independent of age. Uneven hydration is related to the juxtaposition of both hydrated and dry areas corresponding to some hyperpigmented and hyperkeratosic areas. Moreover, capacitance images reveal that some of the hyperpigmented areas may exhibit under- or over-hydrated conditions depending on the nature of the lesion. CONCLUSION: Irregular skin surface hydration is an important characteristic of skin photoaging. It is related to skin pigmentation but does not parallel its unevenness of pigmentation.

A new technique to in vivo study the corneocyte features at the surface of the skin.

PURPOSE OF THE STUDY: To design, develop and validate a new device allowing the features of corneocytes at the surface of the skin to be visualized in vivo and objectively characterized. MATERIALS AND METHODS: Monochromatic light is focused at the proximal end of a coherent bundle of optical fibres. Fluorescence of skin, stained with fluorescein, is then captured by the same fibre bundle and displayed, through a dichroic mirror, by a CCD camera. Fluorescence images are analysed using dedicated software to measure the projected area of cells. RESULTS: The new device allows the mean projected area of corneocytes to be routinely studied and quantified on most of the skin areas of the human body. Measurements carried out on two age groups of women confirm that corneocyte size on the forearm is smaller in young women than in older women. CONCLUSION: The new non-invasive device is easy to use and appear quite appropriate for cutaneous investigations carried out in clinical research.

Influence of age and hormone replacement therapy on the functional properties of the lips.

AIMS: To investigate the influence of age and hormonal status on some functional properties of the lips of women. METHODS: Lips properties were measured and compared through four groups of women (young with normal menses, aged with normal menses, aged and menopaused, aged, menopaused receiving hormonal replacement therapy). The following parameters were recorded: sebum excretion rate on the forehead. On the lower lip: TEWL, mechanical damping, color, tactile acuity. Moreover, capacitance images of each lips were recorded and the mean capacitance measured. RESULTS: Changes in TEWL, mechanical damping and tactile acuity appear clearly linked to age while the increase in lip darkness could be due to hormones. Sebum excretion rate is also clearly linked to hormonal status. Surprisingly, no changes of lips capacitance were detected vs. age or hormonal status. This study confirms that upper lip is more hydrated than the lower one. CONCLUSION: Most of the parameters measured on the lips have similar variations than the same parameters measured on the skin. Only sebum and color appear being dependant on the hormonal status.

Remote in vivo imaging of human skin corneocytes by means of an optical fiber bundle.

Human corneocytes forming the outermost layer of the epidermis (stratum corneum) were imaged in vivo by epifluorescence through a coherent optical fiber bundle. A very simple and rapid method to remotely visualize the cells forming this protective layer of the skin is presented. After the topical application of fluorescein, the distal face of an optical fiber bundle is gently applied perpendicularly onto the labeled skin (contact mode). Remote fluorescence images of the corneocytes are acquired in 50 ms through the bundle comprising 30 000 individually cladded 3.5 microm diameter optical fibers. The very short focal distance which is an intrinsic characteristic of such bundles, allows visualizing only the most superficial monolayer of cells in contact with the external environment. An image displays about 400-500 cells directly on the human body. The size and the arrangement of the corneocytes can thus be acquired and analyzed in a very simple and easy way. The method is flexible and can be used for any location on the human body. Using a gradient-index lens objective (magnification 2.8x) fused to the distal face of the bundle allows the shape of the corneocytes to be better resolved. In addition, the working distance is 300 microm and hence this second approach works in a noncontact imaging mode. Both approaches are complementary and allow providing instantaneously either a global view of the cells with a possible statistical determination of their area or morphological information, which are essential for dermatology and cosmetic sciences. Finally, to improve the quality and the contrast of the recorded images, we tested silica nanoparticles containing fluorescein. In brief, this diagnostic method is nontoxic, painless, easy to use, noninvasive, and nondestructive.

The use of hydroxy acids on the skin: characteristics of C8-lipohydroxy acid.

The hydroxy acids are widely used in skin creams because of their exfoliating and rejuvenating effect on photoaged skin. As a member of this family, the salicylic acid derivative known in the literature as 2-hydroxy-5-octanoyl benzoic acid or beta-lipohydroxy acid has also been proposed as an exfoliant and as a treatment of photoaged skin and acne. This article reviews the effects of the hydroxy acids and compares them to those of the salicylic acid derivative. We propose the name C(8)-lipohydroxy acid (C8-LHA) for this derivative to differentiate it from other related compounds. The lipophilic nature of C8-LHA and its relatively slow penetration in the skin afford it an exfoliating effect that is efficient at low concentrations. It appears to have antimicrobial, anti-inflammatory, and anticomedogenic properties, which make it effective against acne. Its antifungal and exfoliating properties are also likely to prove useful in combating dandruff.

Skin capacitance imaging, a new technique for investigating the skin surface.

Thanks to the recently introduced silicone image sensor technology, skin capacitance imaging has now been made possible. The dedicated device is called SkinChip. This method is easy to handle and provides information about the skin microrelief, the level of stratum corneum hydration and the sweat gland activity. The apparatus sees and measures these parameters with a 50 microm resolution. A series of conditions have been explored using skin capacitance imaging. This review summarizes relevant findings about regional variability on the body, changes occurring with ageing, effects of a hydrating formulation, reactivity kinetics of corneocytes to surfactants, acne and skin pores characteristics, as well as hyperkeratotic dermatoses and tumours.

Early use of PbS nanotechnology for an ancient hair dyeing formula.

Lead-based chemistry was initiated in ancient Egypt for cosmetic preparation more than 4000 years ago. Here, we study a hair-dyeing recipe using lead salts described in text since Greco-Roman times. We report direct evidence about the shape and distribution of PbS nanocrystals that form within the hair during blackening. It is remarkable that the composition and supramolecular organization of keratins can control PbS nanocrystal growth inside a hair.

Capacitance imaging of the skin surface.

BACKGROUND/AIMS: A new device allowing recording capacitance images of the skin surface was recently presented. Parameters, extracted from the gray-level histogram of the images, are tested for a new approach of skin surface hydration measurement in comparison with the classical capacitance method. Illustration of the interest of having both images and parameters for studying the homogeneity and the level of skin surface hydration are presented. METHODS: Software for selecting a region of interest from an image and measuring the parameters derived from its gray-level histogram was used to characterize skin hydration. RESULTS: There is a very close correlation between a Corneometer and the parameters extracted from the SkinChip measurements. The importance of having capacitance images of skin is demonstrated in case of non-homogeneity of the skin hydration, either because of photoaging or following an inflammation process. CONCLUSION: Capacitance imaging is a necessary tool for both completely describing and quantifying skin surface hydration.

Silicon image sensor technology for in vivo detection of surfactant-induced corneocyte swelling and drying.

BACKGROUND: Several instrumental methods can indirectly assess some specific aspects of cutaneous irritation at the level of the stratum corneum (SC). OBJECTIVE: There is a need for developing more sensitive approaches in this field. METHODS: We assessed a recently introduced innovative tool (SkinChip) based on capacitive pixel-sensing technology in its potential to detect early discrete manifestations of skin irritation. The sensor generates a detailed non-optical picture corresponding to a capacitance map of the skin surface reaching 50 microm pixel resolution. Some topographical details can be easily disclosed and the SC hydration as well. Two surfactant solutions were tested on volunteers. These solutions were applied under test patches for 2 days on the volar forearms. Clinical and SkinChip assessments were performed 3 h after removing the patch. RESULTS: The generated images allowed a precise observation of skin irritation which appeared as a two-step process. Early changes consisted of darker pixels corresponding to overhydrated swollen corneocytes at the irritated sites. Two days later, the same area appeared as white pixels, indicating the loss of corneocyte hydration. CONCLUSION: The SkinChip device appears to be a very sensitive tool for detecting the early steps of surfactant-induced skin irritation affecting the SC.

SkinChip, a new tool for investigating the skin surface in vivo.

BACKGROUND/AIMS: Non-invasive methods used for characterizing skin micro-relief and skin surface hydration were developed in the 1980s. Although they allowed some progress in the knowledge of skin properties, they are not completely satisfactory in many aspects. Today, new technologies are emerging that may address such issues. METHODS: We adapted the technology produced by the ST Microelectronics Company for sensing fingerprint for the measurement of skin surface properties. Accordingly, we developed acquisition software for obtaining routinely the distribution of skin surface capacitance along different body sites. Image analysis softwares were also processed for collecting both the main orientations of the micro-relief lines and their density. The average value of skin capacitance is also obtained. RESULTS: The images allow a highly precise observation of the skin topography that can be easily quantified in terms of line density and line orientation. The mean gray levels of the images appear much closely correlated to the Corneometer values. CONCLUSION: This new device appears to be a very convenient way for characterizing the properties of the skin surface. With regard to hydration, it usefully provides both the average value and the hydration chart of the investigated skin zones.

The "Haptic Finger"- a new device for monitoring skin condition.

BACKGROUND/AIMS: Touching the skin is of great importance for the Clinician for assessing roughness, softness, firmness, etc. This type of clinical assessment is very subjective and therefore non-reproducible from one Clinician to another one or even from time to time for the same Clinician. In order to objectively monitor skin texture, we developed a new sensor, placed directly on the Clinician's finger, which generate some electric signal when slid over the skin surface. MATERIAL AND METHODS: The base of this Haptic Finger sensor is a thin stainless steel plate on which sponge rubber, PVDF foil, acetate film and gauze are layered. The signal generated by the sensor was filtered and digitally stored before processing. In a first in vitro experiment, the sensor was moved over different skin models (sponge rubber covered by silicon rubber) of varying hardness and roughness. These experiments allowed the definition of two parameters characterizing textures. The first parameter is variance of the signal processed using wavelet analysis, representing an index of roughness. The second parameter is dispersion of the power spectrum density in the frequency domain, corresponding to hardness. To validate these parameters, the Haptic Finger was used to scan skin surfaces of 30 people, 14 of whom displayed a skin disorder: xerosis (n = 5), atopic dermatitis (n = 7), and psoriasis (n = 2). RESULTS AND CONCLUSION: The results obtained by means of the sensor were compared with subjective, clinical evaluations by a Clinician who scored both roughness and hardness of the skin. Good agreement was observed between clinical assessment of the skin and the two parameters generated using the Haptic Finger. Use of this sensor could prove extremely valuable in cosmetic research where skin surface texture (in terms of tactile properties) is difficult to measure.

EEMCO guidance for the measurement of skin microcirculation.

The blood supply to the skin is provided by a network of arterioles, capillaries and venules organized into a superficial and a deep plexus. The assessment of skin microcirculation is of valuable interest in cosmetology in the quantification of the sun protection factor, skin irritation and efficacy of antiredness treatments. Skin microcirculation can be measured by means of different techniques, based mainly on the quantification of optical and thermal properties of the skin which are modified by the amount of blood perfusion. Relevant and reproducible data can be obtained only through the understanding of the biophysical background of the technique(s) utilized. Standardization of measuring conditions and procedures is particularly required for blood flow assessment. In this paper, the advantages and disadvantages of the main techniques in use are discussed, and optimization of measurements for laser Doppler techniques is described.

Structure and function of human stratum corneum under deformation.

BACKGROUND: The stratum corneum (SC) has an important barrier function. The effect of a mechanical stress applied to the SC is controversial on this important physiological parameter. OBJECTIVES AND METHODS: To assess both in vitro and in vivo the structure and function of human SC submitted to controlled strains, we measured the transepidermal water loss (TEWL), in vivo, on human skin submitted to controlled strains ranging from 0 to 20% extension imposed by a Densi-score device. We also looked at the structure of the SC by means of X-ray diffraction and transmission electron microscopy. RESULTS: Transmission electron microscopy and X-ray diffraction analysis were performed on harvested and stretched human SC. TEWL was not significantly influenced by the relative deformation applied to the skin. At high strain (60%) imposed in vitro to the SC, lipid bilayers and corneosomes were detached from corneocytes. Only rare corneosomes showed internal disruption. X-ray analysis did not reveal modifications in the supramolecular organization of intercellular lipids while stretching the SC. CONCLUSION: Submitting human SC to an extension force up to 20% elongation does not significantly alter the barrier function.

Influence of age on the wrinkling capacities of skin.

BACKGROUND: Comparisons of clinical assessment with measurement of physical parameters are rare. OBJECTIVE: To standardize the horizontal wrinkling of the skin in order to define a reference chart of the different wrinkling grades and to propose an interpretation of the clinical pattern in terms of skin layers thickness and mechanical parameters. METHODS: A device allowing reproducible wrinkling of the skin was made. The skin folds created in this way were clinically assessed on women of different ages. Measurements of the mechanical properties of the skin were carried out by using a Torquemeter. Skin layers' thicknesses were measured by using in vivo Confocal Microscopy (CM) and Ultrasound Imaging (B mode). RESULTS: Skin wrinkling grades increase versus age. Skin elasticity, extensibility and echogenicity decrease also versus age and the wrinkling grade. Wrinkling appears to be related to skin rigidification (for both stratum corneum and dermis) coupled to a certain weakening of the upper dermis (loss of echogenicity). CONCLUSION: This study points out the key role of the age-related alterations of the upper dermis in skin wrinkling capacities.

A computational skin model: fold and wrinkle formation.

This paper presents a computational model for studying the mechanical properties of skin with aging. In particular, attention is given to the folding capacity of skin, which may be manifested as wrinkles. The simulation provides visual results demonstrating the form and density of folds under the various conditions. This can help in the consideration of proper measures for a cosmetic product for the skin.