Assessment of skin moisture. Measurement of electrical conductance, capacitance and transepidermal water loss

Experiments on skin moisture, i.e. the hydration state of the outer epidermis, were undertaken using three different types of equipment, i.e. the Skicon-100 and Corneometer CM 420 hydrometers and the Servo Med EPI evaporimeter. The studies included 10 healthy volunteers. Water was applied to test sites on the forearm and the palm of the hand, and effects monitored by the three methods. Parallel increases in conductance, capacitance and transepidermal water loss were registered for a duration of about 5 min. The Skicon-100 was more sensitive for measurement of increased hydration, while the Corneometer CM 420 might be more sensitive for measurement of decreased hydration. Inter- and intra-individual variations were minor with all instruments. According to reproducibility studies, the Corneometer CM 420 was more accurate than the Skicon-100. Technical experiments indicated that the Corneometer CM 420 depicts changes of hydration down to a depth of 0.1 mm, while the Skicon-100 measures very superficially. In conclusion, both hydrometers were deemed relevant and valid for assessment of skin moisture. The methods are complementary, and their combined use is recommended.     

The relationship between skin surface temperature, transepidermal water loss and electrical capacitance among workers in the fish processing industry: comparison with other occupations

A field study among workers in the fish processing industry (n = 143) was performed to obtain information about skin surface temperature, transepidermal water loss (TEWL), and electrical capacitance and their relationships during work. The skin temperature, TEWL and electrical capacitance were measured on the fingers, hands and forearms. A linear positive relation was found between the temperature and TEWL (in all measured areas), a linear negative relation between the temperature and capacitance (fingers and palms), and a linear negative relation between the capacitance and TEWL (fingers). The results on the fingers among workers in the fish processing industry were compared with results among metal workers (n = 52), cleaners (n = 30), gut cleaners (n = 25), nurses (n = 16), office workers with indoor climate syndrome (n = 20) and normal controls (n = 29). A linear positive relation was found between the respective temperature-TEWL values and a linear negative relation between the respective temperature-capacitance values in the various groups. Furthermore the slope of the temperature-TEWL relations was identical in all groups. Therefore, differences in TEWL levels (comparison at the same temperature) between the respective groups and controls and between the various groups might indicate damage to the skin barrier caused by contact with different irritants and chemicals. However, differences in environment-related variables in the various occupations might also affect TEWL levels. This field study demonstrates, from a practical point of view, how the skin temperature affects TEWL in the various occupations and, as a new point, how sensitive capacitance is to changes in skin temperature. Seasonal variation in TEWL and capacitance was demonstrated among workers in the fish processing industry, with a low TEWL and a high capacitance during summer when the workload is lower.     

The influence of a single application of different moisturizers on the skin capacitance.

Moisturizers are believed to improve the skin condition by increasing the water content of the stratum corneum. A variety of techniques for assessing skin hydration has been developed. In the present study the capacitance following a single application of different moisturizers to normal skin on 12 volunteers was measured with the commercial available Corneometer 420. The moisturizers were pure petrolatum and three oil-in-water creams. The latter contained either glycerine, glycerine and pyrollidone carboxylic acid, or urea as humectant agents. The first measurement of the change in the capacitance was done 2 h after application of the products. All tested products increased the capacitance in the same order of magnitude. For the creams the values were significantly enhanced during the experimental period (6 h). Excess product were removed from some skin areas after the 2 h measurement. This caused immediately a significant decrease in the capacitance of the cream treated sites, whereas a tendency towards higher values were noted on the petrolatum-treated sites. These findings indicate that the non-absorbed components influences the capacitance values. Hence, the interpretation of electrical measurements with respect to skin moisture should be made with caution.     

Friction, capacitance and transepidermal water loss (TEWL) in dry atopic and normal skin

The biophysical properties of non-eczematous skin at three locations in atopics and non-atopics were characterized using non-invasive physical methods. Skin friction was measured with a newly developed sliding friction instrument, the degree of hydration with a capacitance meter (Corneometer CM 820), and the transepidermal water loss (TEWL) was determined using an Evaporimeter EP1. The areas examined (dorsum of the hand, volar forearm and lower back) showed lower values of friction and capacitance in the atopic patients than did corresponding sites in the normal controls. In most areas a significant correlation between friction and capacitance was found. The TEWL was increased in atopic skin, but TEWL seems to correlate neither to friction nor to capacitance.     

Studies on skin surface barrier functions:--skin surface lipids and transepidermal water loss in atopic skin during childhood.

The relationship between skin surface lipids and transepidermal water loss (TWL) was investigated in 22 children with atopic skin. TWL values and casual and replacement lipids were measured by electro-hygrometric and gravimetric methods respectively. Free and total cholesterol and squalene were measured by gas chromatography. The inverse correlations between casual lipids, especially total cholesterol, and TWL exhibited in the normal adult and juvenile skin were not found in the atopic skin. In addition, a significant increase in TWL and decrease in sebaceous lipids was characteristic of atopic skin. In conclusion, the inhibitory action of epidermal cholesterol on TWL is considered to exist only when the skin has a normal keratinization process.     

Quantitative description of human skin water dynamics by a disposition-decomposition analysis (DDA) of trans-epidermal water loss and epidermal capacitance

Background: In vivo water assessment would greatly benefit from a dynamical approach since the evaluation of common related variables such as trans‐epidermal water loss or “capacitance” measurements is always limited to instantaneous data. Mathematical modelling is still an attractive alternative already attempted with bi‐exponential empirical models. A classical two‐compartment interpretation of such models raises a number of questions about the underlying fundamentals, which can hardly be experimentally confirmed. However, in a system analysis sense, skin water dynamics may be approached as an ensemble of many factors, impossible to discretize, but conceptually grouped in terms of feasible properties of the system. The present paper explores the applicability of this strategy to the in vivo water dynamics assessment. Methods: From the plastic occlusion stress test (POST) skin water balance is assessed by modelling trans‐epidermal water loss (TEWL) and “capacitance” data obtained at skin's surface. With system analysis (disposition‐decomposition analysis) the distribution function, H(t), modelled as a sum of exponential terms, covers only the distribution characteristics of water molecules traversing the skin. This may correspond macroscopically to the experimental data accessed by “corneometry”. Separately, the hyperbolic elimination function Q(TEWL ) helps to characterise the dynamic aspects of water influx through the skin. Discussion and conclusion: In the observable range there seems to be a linear relationship between the net amount of water lost at the surface by evaporation, and the capability of the system to replenish that loss. This may be a specific characteristic of the system related to what may be described as the skin's “intrinsic hydration capacity” (IHC) a new functional parameter only identified by this strategy. These new quantitative tools are expected to find different applicabilities (from the in vivo skin characterisation to efficacy testing) contributing to disclose the dynamical nature of the skin water balance process.     

Standardized trauma (tape stripping) in human vulvar and forearm skin. Effects on transepidermal water loss, capacitance and pH.

Mechanical trauma to genital skin may favor the transmission of sexually transmitted diseases. To study differences between vulvar and forearm skin in epidermal repair after standardized trauma, transepidermal water loss, capacitance and pH of forearm and vulvar skin in 10 healthy premenopausal women were monitored for 7 days after a standardized trauma induced by tape stripping to glistening. Vulvar and forearm skin showed similar responses immediately after tape stripping: a sudden increase in transepidermal water loss and capacitance. Forearm skin, however, reacted more intensely than vulvar skin; forearm skin readings remained significantly higher than normal values for 2 days after tape stripping, whereas vulvar skin readings were not significantly different from normal. Thus, vulvar skin did not respond as extensively as forearm skin, presumably because it is a less complete barrier against excess body water loss. On the other hand, vulvar skin seemed to recover faster from skin damage than forearm skin, probably because of its higher epidermal cell turnover.     

Chemometric approach for investigating the skin surface lipids (SSLs) composition: influence of geographical localization

Skin surface lipids (SSLs), arising from both sebaceous glands and skin removal, form a complex lipid mixture composed of free fatty acids and neutral lipids. They are present in the hydrolipidic film and have a close relationship with the stratum corneum lipids. Thus, SSLs participate in the barrier function. One can expect a physiological adaptation of the SSLs composition according to geographical localization or skin pigmentation. In this study, SSLs obtained from three groups of volunteers (light and dark skin, living in France and dark skin, living in Ivory Coast) have been investigated. High-temperature gas chromatography/mass spectrometry has been used to study SSLs composition. The variability in the SSLs chromatographic profiles has been investigated, using chemometric methods which allowed us to highlight the sapienic acid (C16: 1Δ6) as discriminant according to geographical localization. This result is of a great interest regarding sapienic acid properties. However, no significant variation has been detected following skin pigmentation. In parallel, SSLs Raman spectra were collected in order to determine the organization and the conformational order of lipids. The spectral data treatment revealed discriminant variation in the υ C-C stretching region revealing changes in the conformational order of the SSLs following geographical localization.     

Effects of skin moisturizer on the skin barrier dysfunction model: An evaluation of the heel via tape-stripping in healthy,young adults

BackgroundThis study seeks to establish the skin barrier dysfunction model at the heel via tape-stripping (TS) by evaluating the skin moisturizing effects.Materials and methodsNineteen young, female participated in the study. A sequence of TS was performed at the heel and trans-epidermal water loss (TEWL), stratum corneum (SC) hydration, and surface pH were measured. Following TS, the subjects were divided into three groups: moisturizer, emollient, and overcoat. These agents were applied daily at night, and the skin parameters were measured the next morning for a week.ResultsThe TEWL value of TS immediately and 5 min after TS were significantly higher than what was obtained before TS, while the SC hydration after TS was significantly lower than what was obtained before TS. However, there were no significant differences in the skin parameters among the three agents on day 7 after application, with the two-way ANOVA showing no interaction among the agents and number of days.ConclusionThe skin barrier dysfunction model at the heel was established by TS in healthy, young adults. However, the physiological function of the skin at the heel did not change drastically and showed no differences even after continuous application for 7 days.     

The lipometre: An easy tool for rapid quantitation of skin surface lipids (SSL) in man

Summary The purpose of this study is to present a rapid, simple, and accurate method for quantitation of SSL in man. The technique which is derived from the works by Schaefer and Kuhn-Bussius, employs a series of clean ground glass plates, and an apparatus, the Lipometre, for the determination of the variation of light transmission across the plates as a function of the fat deposited on them. Results on 32 adults, males and females, show that the first four interative samplings, at constant pressure, on the same forehead area, follow an identical physical law independently of whether the skin is fatty or dry. This law affords a precise definition of the Casual-Level, its quantification, and its correlation with skin patterns. It is consequently possible, either as an investigative or a routine technique, to predict the total amount of SSL with good accuracy within 2 min. The SSL, for non-pathological skins, fall within the range 150 g/cm² to 900 g/cm² which is in good agreement with values quoted in the literature.     

Irregularity skin index (ISI): a tool to evaluate skin surface texture

Background/aims: Irregularity of skin surface microtopography is difficult to evaluate in Euclidean geometry. Using a fast Fourier transform (FFT), it is possible to convert a space field into a frequency field and to obtain quantitative evaluation of this important feature of the skin. The aim of the present study was to test the applicability of a new parameter, derived from computer assisted FFT, to skin texture, in order to quantify its irregularity. This parameter has the additional advantage of being anisotropic.
Method: The study was conducted on 50 female volunteers. Skin replicas were performed on a healthy area that was not chronically photo-exposed. A new parameter, called "irregularity skin index" (ISI), was identified from FFT. The correlation with volunteers' age was calculated.
Results: ISI was calculated by FFT in two different directions (referred to the x and y axis of the diagram of the FFT and named, respectively, ISIωx and ISIωy). The irregularity skin indexes increased with age of the subjects, showing a correlation with age of r =0.47 (ISIωx) and r =0.51 (ISIωy).
Conclusion: By showing a relatively good correlation with age, ISI seems to be a promising parameter for the study of ageing skin.     

High-frequency conductance measurement of the skin surface hydration state of dry skin using a new probe studded with needle-form electrodes (MT-8C)

Background/aims: When high-frequency conductance measurements are performed on dry scaly skin such as atopic xerosis, senile xerosis or psoriasis, the values recorded with a flat surfaced ordinary probe tend to be lower, indicating a reduced hydration state, than the actual one, because the rough and firm skin surface prevents close contact with the hard and flat surface of the applied probe.
Methods: We evaluated the usefulness of an MT-8C probe (Measurement Technologies Cincinnati, USA), whose skin-attaching portion is studded with 8 needle-like electrodes instead of a flat surfaced type, for measurments on dry skin.
Results/conclusions: The MT-8C probe yielded conductance values slightly higher than those recorded with the flat surfaced probe attached to Skicon in measuring the hydration state of moderately dry skin surface such as atopic xerosis and senile xerosis. It seems to be comparable or more sensitive than the capacitance recording with the Corneometer. The recorded values obtained with the MT-8C probe showed more variations than the latter because of its higher sensitivity and much smaller contact area, that makes it difficult to touch to the same spots repeatedly. No such a difference was observed on severely dry skin and thickly scaly psoriatic lesions.     

The efficacy of a moisturizer (Locobase) among cleaners and kitchen assistants during everyday exposure to water and detergents

Workers exposed to various irritants are widely advised to use moisturizers. To evaluate the efficacy of a moisturizer (Locobase), we studied 111 cleaners and kitchen workers, during everyday exposure to water and detergents. All look part in a standardized interview, After randomization. 1/2 the workers ( n =56) used Locobase during a period of 2 weeks (period L), followed by a period without any emollient (period C). or vice versa( n =5). Clinical assessment and measurements of the skin surface temperature, electrical capacitance and transepidermal water loss (TEWL) were performed on the fingers, hands and arms on entry to the study, after 2 weeks and 4 weeks, or at drop out. The final evaluation showed that 70(63%) were able to complete the study: 23 (21%) completed period L. but withdrew from period C after a mean of 6 days because of progressive dryness of the skin and eczema: and 12 (11%) were excluded because they used topical corticosteroids or emollients. The remaining 6 (5%) participants were lost to follow-up. Clinically, we observed a significant increase in dryness ( p < 0.001) during periods of no treatment (period C), and normalization of the skin texture during use of Locobase. Clinical observations were confirmed by statistically significant differences ( p < 0.001) in the electrical capacitance (epidermal hydration), which decreased during period C and increased to pre-study values during period L. No -significant differences were found in skin temperatures and TEWL rates. Analysis of the questionnaires showed that inability to complete the study (period C) was strongly correlated with incidence of previous skin diseases (irritant and allergic contact dermatitis, atopy, etc.). It is concluded that cleaners and kitchen workers in general benefit from the use of a moisturizer during exposure to various irritants, and that use of a moisturizer seems to be an absolute necessity for 1/3 of the workers.     

A simple and accurate routine procedure for qualitative analysis of skin surface lipids (SSL) in man

Summary A new routine testing procedure of qualitative analysis of skin surface lipids in man is proposed. This method combines the easiness of sampling, by direct contact between ground glass plates and skin fat, with accurate thin layer chromatographic analysis of the five basic parameters (cholesterol, free fatty acids, triglycerides, wax esters, squalene) without any treatment of the samples. Such procedure can be applied to any region of the body.     

Photochemotherapy of psoriasis: effects on bacteria and surface lipids in uninvolved skin

The effect of PUVA therapy for psoriasis on the microbial flora and on levels and composition of skin surface lipid has been studied in ten patients. Samples were obtained from clinically uninvolved skin from the back and the forearm. There was no consistent significant change in the viable counts of aerobic cocci or anaerobic coryneforms during therapy. A transient rise in Staphylococcus aureus counts was thought to be due to the use of emollients rather than to an effect of PUVA. Genetic changes in the microorganisms were not sought. There was an increase in the amount of total lipid (both casual levels and replacement sums) during therapy. An increase of free fatty acids at the expense of triglycerides did not reach statistical significance. The influence of PUVA on the skin flora seems to be less in vivo than anticipated from in vitro studies.     

Two ceramide subfractions detectable in Cer(AS) position by HPTLC in skin surface lipids of non-lesional skin of atopic eczema

The non-involved skin of atopic eczema (NEAE) is characterized by severe dryness and an impaired barrier function of the stratum corneum as indicated by an increased transepidermal water loss. Previous studies have demonstrated that this barrier impairment coincides with marked alterations in the amount and composition of stratum corneum ceramides. The aim of this study was to identify specific alterations in NEAE that may be used in the diagnosis of the atopic eczema. Using a classical procedure for high performance thin layer chromatography we could confirm earlier results: apart from Cer(EOH), which contains omega-hydroxy fatty acid (O) ester-linked to linoleic acid (E) and amide-linked to 6-hydroxy-4-sphingenine (H), the quantities of all ceramide fractions were significantly decreased. Furthermore, Cer(EOH)/Certotal was significantly increased, whereas the percentage of Cer(EOS), which contains sphingosine (S), and Cer(NP), which contains non-hydroxy fatty acid (N) amide-linked to phytosphingosine (P), were significantly decreased. Using a modified procedure for high performance thin layer chromatography we could demonstrate the formation of a double peak in the position of Cer(AS), which contains alpha-hydroxy fatty acid (A), in lipids of NEAE. The subfractions of the double peak comprised 15% and 12% of Certotal. MALDITOF mass spectrometry suggested that the double peak was formed by a homologous series of mono-hydroxylated and mono-unsaturated ceramides of different chain length, e.g., Cer(AS) subfractions containing either (C16,18) or (C22,24,26) alpha-hydroxy fatty acids. In contrast, in normal skin a single peak in Cer(AS) position, which comprised 22% of Certotal, was mainly formed by the long chain subfraction. In some cases this single peak displayed a small shoulder at its right flank, but never showed a clear peak separation when developed with NEAE samples. Furthermore, even in senile xerosis, or in either non-involved skin of psoriasis or seborrhoic eczema, only a single peak occurred in Cer(AS) position. Accordingly, the double peak might be specific for NEAE and turn out to be a marker for atopic eczema.