International Journal of Cosmetic Science, 2010, 32, 410–421

doi: 10.1111/j.1468-2494.2010.00584.x

Review Article

Bioengineering and subjective approaches to the clinical evaluation of dry skin A. J. Byrne Oriflame Research and Development Ltd, Bray Business Park, Kilruddery, Bray, Co. Wicklow, Ireland

Received 16 July 2009, Accepted 18 January 2010

Keywords: dry skin, moisturization, stratum corneum, xerosis

Synopsis

Re´sume´

Dry skin (also known as xerosis) is a cutaneous reaction pattern indicative of abnormal desquamation, which has not only cosmetic considerations, but can also lead to the penetration of irritants and allergens through the stratum corneum (SC). Over the last few decades, our understanding of the structure, composition, formation and function of the SC has advanced tremendously; however, despite these advancements, the occurrence of dry skin remains prevalent in the adult population. The clinical evaluation of dry skin is therefore of significant importance to the cosmetic industry not only for understanding the condition but also for measuring the effects of treatment. Traditionally, dry skin has been evaluated by visual inspection, however, recently a variety of bioengineering techniques have emerged enabling the investigator to objectively assess the extent of xerotic conditions. The most frequently employed methods for the evaluation of dry skin are discussed in this review, including regression testing, squametry, measurement of transepidermal water loss, epidermal hydration, profilometry, confocal Raman spectroscopy, optical coherence tomography, in vivo confocal microscopy and magnetic resonance imaging.

La peau se`che (ou xe´rose) est un mode`le de re´action cutane´ repre´sentant une desquamation anormale. Elle a non seulement des conside´rations cosme´tiques, mais peut e´galement mener a` la pe´ne´tration d’irritants et d’allerge`nes via le stratum corneum. Au cours de ces dernie`res de´cennies, notre compre´hension de la structure, la composition, la formation et la fonction du stratum corneum (SC) ont e´norme´ment progresse´; cependant malgre´ ces progre`s, la pre´sence de peau se`che reste re´pandue dans la population adulte. L’e´valuation clinique de la peau se`che est donc d’une grande importance a` l’industrie cosme´tique non seulement pour comprendre cet e´tat, mais e´galement pour mesurer les effets des traitements. Traditionnellement, la peau se`che a e´te´ e´value´e par l’examen visuel, plus re´cemment une varie´te´ de techniques de bio inge´nierie est apparue permettant d’e´valuer objectivement l’e´tendue des conditions de la xe´rose. Les me´thodes le plus fre´quemment employe´es pour l’e´valuation de peau se`che sont discute´es dans cette revue, y compris le test visuel des crite`res de Kligman, la squamame´trie, la mesure de la perte d’eau transe´pidermique, l’hydratation e´pidermique, la profilome´trie, la spectroscopie confocale Raman, la tomographie optique, la microscopie confocale in vivo et l’imagerie par re´sonance magne´tique.

Correspondence: A. J. Byrne, Oriflame Research and Development Ltd, Bray Business Park, Kilruddery, Bray, Co. Wicklow, Ireland. Tel.: +353 1 273 5379; fax: +353 1 273 5350; e-mail: [email protected], www. oriflame.com

Introduction

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Dry skin is a cutaneous reaction pattern characterized by the collection of corneocytes on the surface of the skin, resulting in a rough texture and

ª 2010 The Author. Journal compilation ª 2010 Society of Cosmetic Scientists and the Socie´te´ Franc¸aise de Cosme´tologie

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Clinical evaluation of dry skin by bioengineering and subjective approaches

appearance [1, 2]. The occurrence of dry skin is dependant on many extrinsic factors including climate, environment and exposure to soaps, detergents, chemicals or medications [1]. There is also a variety of intrinsic factors that can contribute to the condition, such as genetics, diseases, hormone imbalances and ageing [2]. Clinically, the signs and symptoms of dry skin may manifest as scaling with a concomitant reduction of mechanical flexibility, in addition to pruritus, flaking, chapping, erythema, pain and stinging [1]. In almost all cases, xerotic skin is rough, lacks suppleness and is dull in appearance. Dry skin occurs predominantly on the legs but may affect the entire skin surface. Many factors may contribute to xerotic conditions, although winter xerosis is primarily a result of low humidity and cold temperature [3]. Over the last few decades, our understanding of the structure, composition, formation and function of the stratum corneum (SC) has advanced tremendously. Despite these advancements, dry skin remains the most common of human skin disorders. The incidence of atopic dry skin conditions in adults is estimated to be between 2% and 10% [4]. This percentage increases considerably in the young and elderly population and during dry winter months. The clinical evaluation of dry skin is therefore of significant importance to the cosmetic industry not only for understanding the condition but also for measuring the effects of treatment. This review will focus on the most common methods for the evaluation of dry skin, such as the Kligman regression method, squametry, measurement of SC hydration in addition to transepidermal water loss (TEWL). Relatively new techniques, with huge potential for the description of abnormal desquamatory processes are also included, such as confocal Raman spectroscopy, confocal laser scanning spectroscopy, optical coherence tomography (OCT) and magnetic resonance imaging.

Subjective assessment As the concept of dry skin has a well established meaning in the public domain, subjective evaluations of the condition are extremely important. Generally, four- or five-point descriptor scales are used as reliability reduces as the number of assessment points increase [5]. The EEMCO have presented guidelines for the visual evaluation of xerosis which details procedures for clinical evaluation of dry skin using either controlled conditions or casual evaluation [6]. Casual evaluation is directly related to consumer perception as such studies include many de facto variables. Controlled evaluations provide a low signal to noise ratio as variables are eliminated by close control of study parameters [6]. Using examination under ultraviolet light Pierard-Franchimont et al. [7] identified two major types of xerosis according to patterns of scaling. Flexural xerosis (Fig. 1A) was described as cracking in parallel primary lines of the SC. Accretive xerosis (Fig. 1B) refers to hyperkeratosis of the plateaux defined by the criss-cross pattern of the skin surface. Flexural xerosis is the mildest form and is related to repetitive mechanical stresses or friction applied to restricted SC. Accretive xerosis corresponds to the aggregation of large squames as observed in ichthyoses. Kligman’s criteria are regarded as the standard for the visual assessment of dry skin severity. The extent of the condition is assessed using a fourpoint scale: Grade 1: healthy skin, no visible signs of dryness and a healthy sheen and glow. Grade 2: indicates mild xerosis, characterized by small flakes of dry skin and whitening of dermatoglyphic triangles. Grade 3: moderate xerosis; appearance of small, dry flakes causing a powdery appearance. Corners of the dermatoglyphic triangles start to uplift.

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Figure 1 (a) Flexural xerosis. (b) Accretive xerosis [7].

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Visual dryness

tions [8–11]. Refinements to the procedure include alterations in basic parameters such as climate, panellist recruitment criteria, application procedures, study duration and the introduction of solvent barrier disruption. Tape stripping N is significantly (P < 0.05) different to all other products at days 3, 5, 7, 10 & 14

Figure 2 Typical Kligman regression result (top line refers to untreated control) [24].

Grade 4: well-defined xerosis with the entire length of a number of dermatoglyphic triangles uplifted to generate large, dry flakes. Roughness and redness are readily apparent. The Kligman Regression model is an extremely useful and widespread clinical design for the assessment of SC moisturization. This type of clinical design involves daily moisturizer application to the outer lateral aspects of the lower legs for a specified period of time, followed by a regression period of no treatment. Efficacy is assessed visually using the Kligman scale as described above. A typical Kligman result is illustrated in Fig. 2. The popularity of the technique may be due to the fact that it allows the assessor to distinguish between therapeutic as opposed to cosmetic moisturisers. The original regression design was carried out for a period of 4–6 weeks; however, the technique has been subject to many improvements and modifica-

The characteristic disturbance of epidermal differentiation in xerotic skin results in corneocyte aggregation and therefore visible scaling, as opposed to the barely visible desquamation as seen in normal skin [12]. Tape stripping is a sampling method which involves the sequential removal of this superficial scaling portion of the SC using an adhesive substrate [12]. In vivo, tape stripping is carried out by repeated application and removal of an adhesive tape to the surface of the skin. Analysis of samples so obtained can lead to the determination of factors such as SC mass, composition, pH, gene expression, barrier function and percutaneous drug penetration or distribution can be determined [12]. The procedure is minimally invasive, as only corneocytes embedded in a lipid matrix, with no nerve association, are removed. In essence, the technique is a form of mild mechanical insult; however, a homeostatic repair response in the epidermis is quickly initiated after sampling, resulting in the re-establishment of skin barrier function [13]. Although tape stripping is relatively simple and easy to perform there are several parameters that

Surface replication for electron microscopy Skin surface imaging

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Figure 3 Summary of the bioengineering methods available for the clinical evaluation of dry skin [24].

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must be controlled in order to produce meaningful results; these include choice of adhesive tape, skin hydration, cohesion between cells, inter-site and inter-subject variation and relative humidity, time of day, applied pressure, sex, age, clinical alterations and type of adhesive tape used [14–16]. However, adhesive tape stripping does provide a significant advantage to commonly employed instrumental methods for assessing xerotic conditions, principally which it is a fast, simple method and it may provide information regarding topographic details, such as primary and secondary glyphic lines and the geometric patterns which characterize these. Using image analysis of tape stripping, parameters such as squame size, number, optical density and heterogeneity can be determined [17, 18]. Furthermore, tape stripping analysis has been demonstrated to correlate well with visual scoring and to be sufficiently sensitive to measure small changes in scaling that may be difficult to assess in vivo [19, 20]. A natural progression of tape stripping methods is the corneosurfametry assay, in which skin surface cyanoacrylate biopsies are obtained and analysed in order to predict the compatibility of surfactants with the SC and also to determine barrier functionality [21, 22]. Corneosurfamatry is an extremely useful technique for the analysis skin surface affects of applied topical products; however, the technique is relatively invasive and fails to predict potential erythemal reactions in the skin [23]. The objective assessment of dry skin In the past 30 years, there has been an explosion of the development of research tools available for the investigation of numerous parameters relating to skin function, damage and responsiveness treatment [24]. Various bioengineering methods have been developed which allow the operator to objectively any perturbation in SC hydration including; TEWL, electrical impedance (EI), Raman spectrometry, confocal spectroscopy, OCT and magnetic resonance imaging. Each of these techniques is discussed in this section in relation to their usefulness in objectively assessing skin hydration and identifying epidermal abnormalities. Transepidermal water loss The measurement of TEWL is an important noninvasive tool frequently used to monitor changes

in the barrier function of the SC. TEWL measurements are based on the estimation of the water vapour gradient in an open chamber [25]. Water concentration in the skin and flux may be related by Ficks law: J ¼ Km  D  dc =dx where Km = Partition coefficient D = Diffusion coefficient c = Water concentration x = Distance across the SC dc/dx = Water concentration gradient Numerous variables should be taken into consideration when assessing skin TEWL including anatomical variations, age, sex, race, sweat gland activity, circadian rhythm, relative humidity, temperature of the measurement probe and environmental variables [26–31]. Early methods for the assessment of TEWL placed a precisely weighed amount of a hygroscopic salt on the surface the skin, in an unventilated chamber for a defined period. TEWL was measured by weighing the salt before and after treatment [32]. The measurement of TEWL is a widespread and useful method; however, conflicting data have prevented the comprehensive correlation of barrier function with TEWL [2, 33, 34]. This lack of an association, as well as inter-subject and inter-site variation inherent in experimental protocol designs, may explain the difficulty of achieving meaningful conclusions from single TEWL measurements. The plastic occlusion stress test (POST) was devised in order to achieve an improved interpretation of TEWL data. The POST method utilizes occlusion, in order to enhance water flux through the skin therefore increase the response of the whole skin structure. Using the POST technique, novel parameters describing the characteristics of vapour flux through the skin have been described, such as skin surface water loss (SSWL) WHC water holding capacity (WHC), water accumulation velocity (WAV) and water accumulation (WA) [35]. Recent developments in mathematical modelling of the TEWL curves that result from the POST have allowed a more accurate description of variations in skin water flux over time [36–38]. Several commercial available instruments have been devised to measure TEWL. The most widely used techniques may be divided in to two general types; open and closed chambers methods. Openchamber method utilizes a skin capsule which is

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exposed to the atmosphere. Since 1990 Courage and Khazaka have been manufacturing one of the most accepted and best selling open-chamber TEWL measurement devices, the Tewameter. The main advantages of the Tewameter are the small size of the probe head which minimizes the influence of air turbulences inside the probe in addition to the low weight of the probe which exerts no influence on the skin surface structure [25]. DermaLab TEWL is also based on the open-chamber vapour gradient principle. Inside the measurement head, the sensors are protected to eliminate variation caused by air currents and direct incident light [39]. It is extremely important that TEWL results are not susceptible to changes in ambient humidity or air currents. It is therefore desirable to use a closed chamber system, thus reducing the variability of readings, while increasing repeatability and reproducibility; however, closed chamber methods have the obvious drawback of causing skin occlusion. The Delfin VapoMeter is equipped with a closed cylindrical chamber that contains sensors for the measurement of relative humidity [40]. TEWL is calculated from the increase in relative humidity within the chamber. Perturbations of readings as a result of ambient air movements, which is the dominant source of noise in open-chamber TEWL measurements, are absent from VapoMeter data; however, relative humidity in the chamber must decrease to ambient levels before the instrument is ready for consecutive measurements making use of the instrument time consuming. The Aquaflux Biox (Biox Systems Ltd., London, U.K.) is also based on the closed chamber principle and is equipped with a condenser-Chamber to combat the problem of occlusion within the measurement probe [41]. Aquaflux data are extremely accurate and repeatable as the microclimate humidity within the chamber is controlled independently of ambient humidity. Continuous flux vs. time measurements can be recorded for many hours, because the water vapour entering the measurement chamber is continuously removed by the condenser (Fig. 3). Several studies have compared the accuracy and reproducibility of the TEWL methods described above and the data indicates a strong correlation between all the instruments [25, 40, 42, 43]. Open-chamber methods have the advantage of speed of use with the drawback of disturbances from microclimates; whereas closed chamber methods generally have the disadvantage

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of being time consuming to perform, with the advantage of resultant data being independent from external air movements. Stratum corneum hydration Electrical impedance (EI) is defined as total electrical resistance of the skin to an alternating current. The measurement of the impedance of the skin has been studied extensively and is the most widely used technique to assess the water content of the horny layer. Rosendal et al. [44] first demonstrated that the electrical properties of the skin are directly related to the water content of the SC. Alterations in epidermal hydration will result in changes in electrical properties of the SC manifested by an increased SC capacitance, conductance and impedance values [45]. It has also been demonstrated the EI readings are dependent on skin lipid content and may therefore, be ideally placed for the evaluation of xerotic conditions [46, 47]. There are numerous commercially available instruments based on the principle of EI/capacitance and several studies have been carried out to compare the performance of each [48–51]. The Corneometer (Courage and Khazaka, GmbH, Cologne, Germany) is based on the capacitance principle and is probably the most widely used instrument of the type due to high reproducibility, ease of handling and short measurement time [51]. The probe of the corneometer is made of two metal plates positioned in close proximity, separated from the skin surface by a glass lamina in order to prevent current conduction [49]. Silicon image sensor technology has also been applied to assess SC hydration and skin surface topography via SkinChip Imaging (SCI, L¢Oreal, Paris, France). The SkinChip device contains 92 160 capacitors located every 50 lm over a 18 · 12.8-mm plate [52]. SCI scans generate a capacitance map of the skin surface by specifically developed image capture software. SCI correlates positively with corneometer data and furthermore, SCI measurements have been used successfully to describe psoriasis and SC hydration, in addition to the analysis of acne lesions, seborrheic keratoses and melanocytic naevi [53–55]. The Nova Dermal Phase Meter (Nova Technology Corporation, Gloucester, MA, U.S.A.) is an impedance-based capacitive instrument with a probe consisting of two concentric electrodes and uses frequencies of up to 1 MHz in order to measure the outer SC layers. As such, the

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instrument is not discriminative for dry skin when the skin is very dry a zero reading will be observed [32]. The Skicon principle (I.B.S., Hamamatsu-shi, Japan) is based on the conductance principle and uses a probe system consisting of two concentric electrodes separated by a phenolic insulator [10, 49]. The device measures at a high frequency (3.5 MHz) in order to measure the outer SC layers [32]. The DermaLab (Cortex Technology, Handsund, Denmark) is an EI-based device with a probe of three concentric electrodes. The MoistureMeter (Delfin Technologies Ltd, Kuopio, Finland) relates both the capacitive and conductive properties of tissues to the water content using an open-ended co-axial probe [42]. The most obvious drawback to measurement of water using EI is that substances other than water may influence impedance or resistance to flow [56]. For example, humectants (such as glycerine) and salts will alter impedance while urea, a common component of moisturisers, is known to alter the dipole moment of keratin [55]. In fact, Bielfeldt et al. [57] recently demonstrated a positive correlation of capacitance readings with confocal Raman Spectroscopy data, but a lack of correlation of Raman readings with SC water content. Furthermore, the only correlation found between the methods was for water content in the lower epidermal layers. These observations were ascribed to a limited penetration depth of the instrument’s capacitor field in addition to a reduction in field density with distance to the measurement probe. The data seem to be supported by near infrared (NIR) spectroscopy studies which indicate that impedance and capacitance measurements are relatively insensitive to small changes in dry skin score [58]. Skin profilometry Skin topographical details can provide useful parameters for the analysis of dry skin. One of the most common techniques to analyse skin topography is to cast silicone replicas using dental impression material. Several silicon materials are available including Silflo (e.g. Potters Bar, Hertfordshire, U.K.) and silicone mass (e.g. SilasoftN, Detax GmbH and Co., Ettlingen, Germany). Both materials are initially a viscous, elastic mass which polymerizes several minutes after addition of a catalyst [59]. The fluidity of the material upon contact with the skin allows the fine details of the

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skin to be replicated. There are several methods available to analyse replicas so taken, including image analysis, grey level analysis, laser profilometry, transparency profilometry and more recently, fringe projection [59, 60]. The most obvious disadvantage to skin surface replicas is that upon application the skin surface is disturbed as is any abnormal scaling patterns, the technique is therefore not ideal for the evaluation of dry, scaly conditions [10]. Direct photographic images of skin topography in vivo, have limited usefulness in the evaluation of dry skin; however, several specialized imaging techniques have been developed. For example, Hayashi et al. utilized dansyl chloride staining in conjunction with UV illumination and highly standardized photography in order to measure SC turnover rate [61]. The Visioscan (Courage and Khazaka, GmbH, Cologne, Germany) is a specialized UV-A light video camera which produces high-contrast maps of microrelief parameters, epidermal melanization and desquamation [62]. The images produce have been used effectively to demonstrate the fine detail of skin structure and dryness level [63]. Confocal Raman spectroscopy Current industry standard techniques used to determine water content and the extent of xerotic conditions provide no quantitative information regarding the actual water distribution in the SC, SC thickness or the molecular composition of the skin. Raman spectroscopy is a non-destructive, non-invasive technique which can be used to monitor skin hydration depth profiles (Fig. 4), water gradients in tissue, drug delivery profiles and NMF composition [1]. Detailed information regarding the molecular composition of the skin can be read from the positions, relative intensities and shapes of the bands in the acquired Raman spectra [64]. The principle of confocal Raman spectroscopy relies on the inelastic scattering, or Raman scattering, of monochromatic light, to study the vibrational, rotational and other low-frequency modes of a system [65]. In a typical Raman experiment, a discrete quantity of energy is transferred to a molecule, resulting in the excitation of the vibrational mode of the system. The energy required to excite an electron to a higher vibrational state depends on the environment in which it exists; therefore, information regarding molecular structure, molecular

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Figure 4 Differences in the depth profiles of water content in the forearm skin before and after hydration with watersoaked cotton wool for (a) 1.5 min (b) 15 min (c) 50 min and (d) 90 min [70].

interactions, and the chemical environment of the molecule may be deduced in a highly specific manner [64]. The first commercially available in vivo confocal Raman microspectropic technique was manufactured by River Diagnostics; the instrument has been shown to accurately measure water depth profiles and concentrations in human skin [66]. Several publications have described the measurement of water and water gradients in the SC. The argument for the existence of a SC water gradient was first put forward by Warner et al. [67] resulting from experiments on rapidly frozen skin. Using electron probe analysis and electron microscopy it was demonstrated that the water content of the basal epidermal layers remains relatively constant, whereas a significant discontinuity in hydration state exists between the upper granular layers. Blank et al. [68] calculated the thickness of the hydrated SC and the permeability and diffusion constants SC water, in vitro, leading to the conclusion that a single diffusion constant for water applies to the SC and that SC water is in a constant flux i.e. there must be a linear hydration gradient in the SC.

By exposing isolated sheets of SC to environments of varying relative humidity, Obata and Tagami [69] demonstrated that the water content of the innermost layers of the SC remains constant except in conditions of extreme humidity, and that there is an almost completely linear hydration gradient to the outer layers of the skin. More recently, in addition to confirming these observations, Egawa and Tagami [70] also demonstrated that alterations in the concentration gradients of water, free amino acids and lipids in the skin depend on age, anatomical site and season. One of the disadvantages to CFR is relatively insensitive and requires the molecule of interest be present at a sufficient concentration, and exhibit spectral features of sufficient intensity, to permit its differentiation from those of the skin. The output of a confocal Raman experiment is, indeed, a relative concentration rather than an absolute quantification of the analyte. However, application of Raman spectroscopy to the analysis of the molecular composition of the skin is one of the more exciting developments in the field in recent years.

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Confocal microscopy Confocal microscopy is a non-invasive microscopic technique which allows the monitoring of structural components of the skin to the level of the papillary dermis [71]. The first in vivo confocal microscopic images of human skin were obtained using a mercury lamp as light source and a Nipkow disk as scanning device [72]. Subsequently, the technique has been developed for clinical applications, offering real time non-invasive imaging with a resolution near that of conventional histology [72]. Modern in vivo confocal microscopes act by focusing a laser light to small point within the dermal tissue; the system then detects light directly from the focal point and removes any scattered light from out-of-focus planes, producing an image of high resolution [71]. Two formats of in vivo confocal microscopy are available such as reflectance or fluorescent. Reflectance mode confocal microscopy utilizes the inherent refractive index properties of the various cellular microstructures, whereas fluorescent microscopy requires the application of a photophore [24, 71]. Confocal images can clearly visualize epidermal structures, including individual corneocytes and keratinocytes, collagen fibres and circulating blood cells in capillaries [24, 73]. The Lucid Vivascope (Rochester, NY, U.S.A.) is a commercially available reflectance confocal microscope designed specifically for clinical imaging of the skin; using confocal images taken in vivo is possible to identify features of irritant and allergic contact dermatitis, psoriasis, cutaneous infections, skin neoplasmas and melanocytic nevi [73]. In addition, various epidermal parameters directly related to dry skin and xerosis can be measured accurately in vivo, such as keratinocyte size and distribution, skin hydration as well as SC and epidermal thickness [74–76].

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Leeson et al. [75] used a fluorescent contrasting agent to improve resolution and developed an ‘expert cellular morphology grading scale’ linking dry skin severity with confocal fluorescence images (Fig. 5). Optical coherence tomography Optical coherence tomography is a non-invasive optical imaging technique offering millimetre penetration with micrometer-scale axial and lateral resolution [77]. The optical setup typically consists of an interferometer (typically Michelson type) with a low coherence, broad bandwidth light source [77]. OCT imaging is analogous to that of ultrasound imaging as it measures echo delays and reflected infrared light from internal tissue structures [78]. Because the velocity of light is extremely high, direct measurement of optical echoes cannot be performed electronically, as in ultrasound. The spatial resolution in the axial direction is 10–20 lm, which is close to the thickness of the SC [78]. Optical coherence tomography is capable of recording many parameters of relevance to the investigation of dry skin by measurements of distances between peaks, signal intensities and light attenuation coefficients at different depths of the skin. Gambichler et al. [79] investigated variances in epidermal thickness because of age, gender, skin type and anatomic site using OCT. Hendriks et al. [80] reported the correlation of OCT measurements with skin flexibility parameters. The usefulness of OCT, in terms of the assessment of dry skin, is similar to that of confocal reflectance microscopy as many common parameters can be measured by both techniques. However, difference exists in resolution and image quality between the two. Confocal microscopy provides a higher resolu-

Figure 5 Typical cellular morphologies of patients suffering from dry skin (lower outer leg) as observed using fluorescence confocal microscopy. Clinical dry skin scores increase from left to right [75].

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tion than OCT whereas the detection depth and the image size of OCT are much greater [75].

ized, in addition to providing detailed information regarding epidermal hydration.

Magnetic resonance imaging

Concluding remarks

Magnetic resonance imaging is a non-invasive, non-destructive technique which allows the acquisition of detailed information regarding the concentration, local environment and distribution of water molecules in the epidermis. MRI offers the capacity to directly measure the hydration state of the SC, rather than using a variety skin surface parameters to infer molecular changes occurring in the skin [81]. Water protons in the skin are sensitive to the magnetic environment in which they are placed and useful parameters such as distinct phase contrast, magnetization transfer contrast (MTC), specific relaxtivities and chemical shift contrast may be determined using MRI [82]. Until recently, standard MRI techniques have been limited for use on the skin, because of short spin–spin relaxation values in the epidermis resulting in a poor signal [83]. It is now possible to achieve high contrast be between the various epidermal layers [82]. Several investigators have reported the use of MRI to study the effects of skin hydration. Song et al. [82] identified the substantial improvements in signal-to-noise ratio which could be achieved by shortening the echo time. Ablett et al used short echo time (5 ms) in order to observe the outermost layers of the SC [81]. Mirrashed et al. [84, 85] used MTC to improve the resolution of MRI allowing individual layers of the epidermis to be visual-

The methods available for the description of dry skin range from subjective evaluation, such as regression testing, to minimally invasive methods such as squametry, through to totally non-invasive methods for the description of various epidermal parameters. Although the recent advances in bioengineering techniques have added tremendously to our knowledge of the characteristics of dry skin, consumer perception of skin quality is of paramount importance. It is therefore essential that techniques chosen to describe the extent of these conditions directly relate to this perception. Visual evaluation of xerotic conditions, therefore, remains a key technique to record the effects of any disruption in the dry skin cycle. Conversely, there is mounting evidence to suggest that methods such as corneometry are less useful in the evaluation of dry skin, as the technique fails to accurately describe small changes in SC hydration and is subject to interference from topically applied treatments. The combination of subjective approaches with objective measurements is therefore the optimum strategy for the evaluation of dry skin.

References 1. Pons-Guiraud, A. Dry skin in dermatology: a complex physiopathology. J. Eur. Acad. Derm. Venereol. 21, 1–4 (2007). 2. Engelke, M., Ensen, J.M., EkanayakeMudiyanselage, S. and Proksche, E. Effects of xerosis and ageing on epidermal proliferation and differentiation. Br. J. Dermatol. 137, 219–225 (1997). 3. Blank, I. Further observations on factors which influence the water content of the stratum corneum. J. Inv. Dermatol. 21, 259–271 (1953). 4. Bath-Hextall, F. and Williams, H. Skin disorders: Eczema (atopic). BMJ Clin. Evid. 12, 1716 (2007).

Acknowledgements The author would like to thank Dr. A.V. Rawlings and A. LaLoeuf for their assistance in preparing this manuscript.

5. Pierard-Franchimont, C. and Pierard, G.E. Beyond a glimpse at seasonal dry skin: a review. Exog. Dermatol. 1, 3–6 (2002). 6. Serup, J. EEMCO guidance for the assessment of dry skin (xerosis) and ichthyosis: clinical scoring systems. Skin Res. Tech. 1, 109–114 (1995). 7. Pierard-Franchimont, C., Petit, L. and Pierard, G.E. Skin surface patterns of xerotic legs: the flexural and accretive types. Int. J. Cosmet. Sci. 23, 121–126 (2001). 8. Boisits, E.K., Nole, G.E. and Cheney, M.C. The refined regression method. J. Cut. Aging Cosmet. Dermatol. 1, 155–163 (1989). 9. Grove, G. Skin surface hydration changes during a mini-regression

test as measured in vivo by electrical conductivity. Curr. Ther. Res. 52, 556–561 (1992). 10. Van Neste, D. Comparative study of normal and rough human skin hydration in vivo: evaluation with four different instruments. J. Dermatol. Sci. 2, 119–124 (1991). 11. Matts, P.J., Gray, J. and Rawlings, A.V. Disrupting the dry skin cycle Clinical efficacy. In: The ‘Dry Skin Cycle’- A New Model of Dry Skin and Mechanisms for Intervention (Matts, P.J. and Rawlings, A.V., eds.). The Royal Society of Medicine Press Limited, U.K (2005). 12. Escobar-Cha´vez, J.J., Merino-Sanjua´n, V., Lo´pez-Cervantes, M., et al. The tape-stripping technique as a

ª 2010 The Author. Journal compilation ª 2010 Society of Cosmetic Scientists and the Socie´te´ Franc¸aise de Cosme´tologie 418

International Journal of Cosmetic Science, 32, 410–421

A. J. Byrne

Clinical evaluation of dry skin by bioengineering and subjective approaches

13.

14.

15.

16.

17.

18.

19.

20.

21.

22.

23.

method for drug quantification in skin. J. Pharm. Pharmaceut. Sci. 11, 104–130 (2008). Smith, W. Stratum corneum barrier integrity controls skin homeostasis. Int. J. Cosmet. Sci. 21, 99–106 (1999). Bashir, S.J., Chew, A.L., Anigbogu, A., et al. Physical and physiological effects of stratum corneum tape stripping. Skin Res. Technol. 7, 40– 48 (2001). Breternitz, M., Flach, M., Prassler, J., et al. Acute barrier disruption by adhesive tapes is influenced by pressure, time and anatomical location: integrity and cohesion assessed by sequential tape stripping; a randomized, controlled study. Br. J. Dermatol. 156, 231–240 (2007). Zhai, H., Dika, E., Goldovsky, M., et al. Tape-stripping method in man: comparison of evaporimetric methods. Skin Res. Technol. 13, 207–210 (2007). Voegeli, R., Heiland, J., Doppler, S., et al. Efficient and simple quantification of stratum corneum proteins on tape strippings by infrared densitometry. Skin Res. Technol. 13, 242–251 (2007). Loffler, H., Dreher, F. and Maibach, H.I. Stratum corneum adhesive tape stripping: influence of anatomical site, application pressure, duration and removal. Br. J. Dermatol. 151, 746–752 (2004). Black, D., Boyer, J. and Lagarde, J.M. Image analysis of skin scaling using D-squame samplers: comparison with clinical scoring and use for assessing moisturizer efficacy. Int. J. Cosmet. Sci. 28, 35–44 (2006). De Paepe, K.J., Hachem, J.P., Roseeuw, D., et al. Squamometry as a screening method for the evaluation of hydrating products. Skin Res. Technol. 7, 184–192 (2001). Goffin, V., Pierard-Franchimont, C. and Pierard, G.E. Microwave corneosurfametry: a minute assessment of the skin compatibility of surfactantcontaining products. Skin Res. Technol. 3, 242–244 (1997). Uhoda, E., Goffin, V. and Pierard, G.E. Responsive corneosurfametry following in vivo skin preconditioning. Contact Derm. 49, 292–296 (2004). Gabard, B., Chatelain, E. and Bieli, E. et al. Surfactant irritation: in vitro corneosurfametry and in vivo bioen-

24.

25.

26.

27.

28.

29.

30.

31.

32.

33.

34.

35.

gineering. Skin Res. Technol. 7, 49– 55 (2002). Rawlings A.V., Matts.P.J., Matts, P.J. and Anderson, C.D., et al.. Skin biology, xerosis, barrier repair and measurement. Drug Discov. Today Dis. Mech. 5, e127–e136 (2008). Rosado, C., Pinto, P. and Rodrigues, L.M. Comparative assessment of the performance of two generations of Tewameter: TM210 and TM300. Int. J. Cosmet. Sci. 27, 237–241 (2005). Rodrigues, L. and Pereira, L.M. Basal transepidermal water loss: right/left forearm difference and motoric dominance. Skin Res. Technol. 4, 135– 137 (1998). Chilcott, R.P. and Farrar, R. Biophysical measurements of human forearm skin in vivo: effects of site, gender, chirality and time. Skin Res. Technol. 6, 64–69 (2000). Cravello, B. and Ferri, A. Relationships between skin properties and environmental parameters. Skin Res. Technol. 14, 180–186 (2000). Hildebrandt, D., Ziegler, K. and Wollina, U. Electrical impedance and transepidermal water loss of healthy human skin under different conditions. Skin Res. Technol. 4, 130–134 (1998). Thomas, S., Welzel, J. and Wilhelm, K.P. Relationship between transepidermal water loss and temperature of the measuring probe. Skin Res. Technol. 3, 73–80 (1997). Chou, T.Z., Lin, K.H., Lee, S.M., et al. Transepidermal water loss and skin capacitance alterations among workers in an ultra-low humidity environment. Arch. Dermatol. Res. 296, 489–495 (2005). Lambers, H. and Pronk, H. Biophysical methods for stratum corneum characterization. In: Cosmetic Lipids and the Skin Barrier (Forster, T., ed.). Marcel Dekker Inc, U.K (2002). Berry, N., Charmeil, C., Goujon, C., et al. A clinical, biometrological and ultrastructural study of xerotic skin. Int. J. Cosmet. Sci. 21, 241–252 (1999). Chilcott, R.P., Dalton, C.H., et al. Transepidermal water loss does not correlate with skin barrier function in vitro. J. Invest. Dermatol. 118, 871–875 (2002). Beradesca, E. Dynamic measurements: the plastic occlusion stress test (POST) and the moisture accumulation test (MAT). In: Bioengi-

36.

37.

38.

39.

40.

41.

42.

43.

44.

45.

46.

neering of the Skin: Water and the Stratum Corneum (Raton, B. ed.), CRC Press, Taylor & Francis Group, London, U.K. (1994). Rosado, C., Pinto, P. and Rodrigues, L.M. Modelling TEWL-desorption curves: a new practical approach for the quantitative in vivo assessment of skin barrier. Exp. Dermatol. 14, 386–390 (2005). Rodrigues, L.M., Pinto, P.C. and Pereira, L.M. Quantitative description of human skin water dynamics by a disposition-decomposition analysis (DDA) of transepidermal water loss and epidermal capacitance. Skin Res. Technol. 9, 24–30 (2003). Rodrigues, L., Pinto, P., Galego, N., et al. Transepidermal water loss kinetic modeling approach for the parameterization of skin water dynamics. Skin Res. Technol. 5, 72– 82 (1999). Grove, G.L., Grove, M.J., Zerweck, C., et al. Comparative metrology of the evaporimeter and the DermaLab TEWL probe. Skin Res. Technol. 5, 1– 8 (1999). De Paepe, K., Houben, E., Adam, R., et al. Validation of the VapoMeter, a closed unventilated chamber system to assess transepidermal water loss vs. the open chamber Tewameter. Skin Res. Technol. 11, 61–69 (2005). Imhof, R.E., Berg, E.P., Chilcott, R.P., et al. New instrument for measuring water vapour flux density from arbitrary surfaces. IFSCC Mag. 54, 297– 301 (2002). Alanen, E., Nuutinen, J., Nickle´n, K., et al. Measurement of hydration in the stratum corneum with the MoistureMeter and comparison with the Corneometer. Skin Res. Technol. 10, 32–37 (2004). Kramer, B.I. Open-chamber and Condenser-chamber TEWL Methods: Mathematical Model and Experimental Comparisons. SCC Annual Scientific Meeting & Technology Showcase. Society of Cosmetic Chemists, New York (2007). Rosendal, T. Concluding studies on the conducting properties of human skin to alternating current. Acta Physiol. Scand. 9, 39–45 (1945). Berardesca, E. EEMCO guidance for the assessment of stratum corneum hydration: electrical methods. Skin Res. Technol. 3, 126–132 (1997). Nicander, I., Norlen, L., Brockstedt, U., et al. Electrical impedance and

ª 2010 The Author. Journal compilation ª 2010 Society of Cosmetic Scientists and the Socie´te´ Franc¸aise de Cosme´tologie International Journal of Cosmetic Science, 32, 410–421

419

Clinical evaluation of dry skin by bioengineering and subjective approaches

47.

48.

49.

50.

51.

52.

53.

54.

55.

56.

57.

other physical parameters as related to lipid content of human stratum corneum. Skin Res. Technol. 4, 213– 221 (1998). Nicander, I. and Ollmar, S. Clinically normal atopic skin vs. non-atopic skin as seen through electrical impedance. Skin Res. Technol. 10, 178–183 (2004). Fluhr, J.W., Gloor, M., Lazzerini, S., et al. Comparative study of five instruments measuring stratum corneum hydration (Corneometer CM 820 and CM 825, Skicon 200, Nova DPM 9003, DermaLab). Part II. In vivo. Skin Res. Technol. 5, 171–178 (1999). Clarys, P., Barel, A.O. and Gabard, B. Non-invasive electrical measurements for the evaluation of the hydration state of the skin: comparison between three conventional instruments - the Comeometer, the Skicon and the Nova DPM. Skin Res. Technol. 5, 14–20 (1999). Judi, M.Ø. The effect of 3 moisturisers on skin surface hydration. Skin Res. Technol. 2, 32–36 (1996). O’Goshi, K.I. and Serup, J. Interinstrumental variation of skin capacitance measured with the Corneometer. Skin Res. Technol. 11, 107–109 (2005). Xhauflaire-Uhoda, E. and Pierard, G.E. Skin capacitance imaging of acne lesions. Skin Res. Technol. 13, 9–12 (2007). Diridollou, S., de Rigal, J., Querleux, B., et al. Comparative study of the hydration of the stratum corneum between four ethnic groups: influence of age. Int. J. Dermatol. 46 (Suppl. 1), 11–14 (2007). Xhauflaire-Uhoda, E., Pierard-Franchimont, C. and Pierard, G.E. Skin capacitance mapping of psoriasis. J. Eur. Acad. Dermatol. Venereol. 20, 1261–1265 (2006). Xhauflaire-Uhoda, E. and Pierard, G.E. Contrasted skin capacitance imaging of seborrheic keratoses and melanocytic naevi. Dermatology 212, 394–397 (2006). Grove, G.L., Zerweck, C. and Pierce, E. Non-invasive instrumental methods for the assessment of moisturisers. In: Skin Moisturisation. (Leyden, J.J. and Rawlings, A.V. eds.), pp. 499–528, 1st edn. Marcel Dekker, New York (2002).. Bielfeldt, S., Schoder, V., Ely, U., et al. Assessment of human stratum

58.

59.

60.

61.

62.

63.

64.

65.

66.

67.

corneum thickness and its barrier properties by in vivo confocal Raman spectroscopy. IFSCC Mag. 12, 9–15 (2009). Zhang, S.L., Meyers, C.L., Subramanyan, K., et al. Near infrared imaging for measuring and visualizing skin hydration. A comparison with visual assessment and electrical methods. J. Biomed. Optics 10, 031107 (2005). Fischer, T.W., Wigger-Alberti, W. and Elsner, P. Direct and non-direct measurement techniques for analysis of skin surface topography. Skin Pharmacol. Appl. Skin Physiol. 12, 1–11 (1999). Akazaki, S. and Imokawa, G. Mechanical methods for evaluating skin surface architecture in relation to wrinkling. J. Dermatol. Sci. 27, 5– 10 (2001). Hayashi, S., Matsue, K. and Takiwaki, H. Image analysis of the distribution of turnover rate in the stratum corneurn. Skin Res. Tech. 4, 109–120 (1988). Xhauflaire-Uhoda, E., Pierard-Franchimont, C., Pierard, G.E., et al. Weathering of the hairless scalp: a study using skin capacitance imaging and ultraviolet light-enhanced visualization. Clin. Exp. Dermatol. 35, 83–85 (2010). Hermanns, J.F., Petit, L. and Martalo, O. Unraveling the patterns of subclinical pheomelanin-enriched facial hyperpigmentation: effect of depigmenting agents. Dermatology 201, 118–122 (2000). Caspers, P.J., Lucassen, G.W., Carter, E.A., et al. In Vivo confocal Raman microspectroscopy of the skin: noninvasive determination of molecular concentration profiles. J. Invest. Dermatol. 116, 434–442 (2001). Prasch, T. and Forster, T. Detection of cosmetic changes in skin surface lipids by infrared and Raman spectroscopy. In: Cosmetic Lipids and the Skin Barrier (Forster, T., ed.). Marcel Dekker Inc, New York (2002). Wu, J. and Polefka, T.G. Confocal Raman microspectroscopy of stratum corneum: a pre-clinical validation study. Int. J. Cosmet. Sci. 30, 47–56 (2008). Warner, R.R., Myers, M.C. and Taylor, D.A. Electron probe analysis of human skin: determination of the water concentration profile. J. Invest. Dermatol. 90, 218–224 (1988).

A. J. Byrne

68. Blank, I.H., Moloney, J., Emslie, A.G., et al. The diffusion of water across the stratum corneum as a function of its water content. J. Invest. Dermatol. 82, 188–194 (1984). 69. Obata, M. and Tagami, H. Electrical determination of water content and concentration profile in a simulation model of in vivo stratum corneum. J. Invest. Dermatol. 92, 854–859 (1989). 70. Egawa, M. and Tagami, H. Comparison of the depth profiles of water and water-binding substances in the stratum corneum determined in vivo by Raman spectroscopy between the cheek and volar forearm skin: effects of age, seasonal changes and artificial forced hydration. Br. J. Dermatol. 158, 251–260 (2008). 71. Meyer, L.E., Otberg, N., Sterry, W., et al. In vivo confocal scanning laser microscopy: comparison of the reflectance and fluorescence mode by imaging human skin. J. Biomed. Opt. 11, 044012 (2006). 72. Caspers, P.J., Lucassen, G.W. and Puppels, G.J. Combined in vivo confocal Raman spectroscopy and confocal microscopy of human skin. Biophys. J. 85, 572–580 (2003). 73. Gonza´lez, S. and Gilaberte-Calzada, Y. In vivo reflectance-mode confocal microscopy in clinical dermatology and cosmetology. Int. J. Cosmet. Sci. 30, 1–17 (2008). 74. Huzaira, M., Rius, F., Rajadhyaksha, M., et al. Topographic variations in normal skin, as viewed by in vivo reflectance confocal microscopy. J Invest. Dermatol. 116, 846–852 (2001). 75. Leeson, D.T., Lynn Meyers, C. and Subramanyan, K. In vivo confocal fluorescence imaging of skin surface cellular morphology: a pilot study of its potential as a clinical tool in skin research. Int. J. Cosmet. Sci. 28, 9– 20 (2006). 76. Nouveau-Richard, S., Monot, M., Bastien, P., et al. In vivo epidermal thickness measurement: ultrasound vs. confocal imaging. Skin Res. Technol. 10, 136–140 (2004). 77. Welzel, J. Optical coherence tomography in dermatology: a review. Skin Res. Technol. 7, 1–9 (2001). 78. Salvini, C., Massi, D., Cappetti, A., et al. Application of optical coherence tomography in non-invasive characterization of skin vascular lesions. Skin Res. Technol. 14, 89–92 (2008).

ª 2010 The Author. Journal compilation ª 2010 Society of Cosmetic Scientists and the Socie´te´ Franc¸aise de Cosme´tologie 420

International Journal of Cosmetic Science, 32, 410–421

Clinical evaluation of dry skin by bioengineering and subjective approaches

79. Gambichler, T., Matip, R., Moussa, G., et al. In vivo data of epidermal thickness evaluated by optical coherence tomography: Effects of age, gender, skin type, and anatomic site. J. Dermatol. Sci. 44, 145–152 (2006). 80. Hendriks, F.M., Brokken, D. and Oomens, W.J., et al. Influence of hydration and experimental length scale on the mechanical response of human skin in vivo, using optical coherence tomography. Skin Res. Technol. 10, 231–241 (2004). 81. Ablett, S., Burdett, N.G., Carpenter, T.A., Hall, L.D. and Salter, D.C.

Short echo time MRI enables visualisation of the natural state of human stratum corneum water in vivo. J. Magn. Reson. Imaging 14, 357–360 (1996). 82. Song, H.K., Wehrli, F.W. and Ma, J. In vivo MR microscopy of the human skin. Magn. Reson. Imaging 37, 185– 191 (1997). 83. Mirrashed, F. and Sharp, J.C. In vivo morphological characterisation of skin by MRI micro-imaging methods. Skin Res. Technol. 10, 149–160 (2004). 84. Mirrashed, F., Sharp, J.C., Krause, V., Morgan, J. and Tomanek, B. Pilot

A. J. Byrne

study of dermal and subcutaneous fat structures by MRI in individuals who differ in gender, BMI, and cellulite grading. Skin Res. Technol. 10, 161–168 (2004). 85. Mirrashed, F. and Sharp, J.C. In vivo quantitative analysis of the effect of hydration (immersion and Vaseline treatment) in skin layers using highresolution MRI and magnetisation transfer contrast. Skin Res. Technol. 10, 14–22 (2004).

ª 2010 The Author. Journal compilation ª 2010 Society of Cosmetic Scientists and the Socie´te´ Franc¸aise de Cosme´tologie International Journal of Cosmetic Science, 32, 410–421

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