Depth profile of diffuse reflectance near-infrared spectroscopy for measurement of water content in skin

BACKGROUND/PURPOSE: The penetration depth of light in diffuse reflectance near-infrared spectroscopy for measuring water content in skin is assessed both from theoretical and experimental points of view. METHODS: The Monte Carlo simulation was implemented to investigate the dependencies of the light penetration depth on a source-detector distance. To compare with the simulation results, an in vivo experiment for water contents of skin was performed introducing two different optical fiber probes. RESULTS: It is found that the minimum separation between a source and detector fibers influences largely the measurement depth. The larger separation leads to a deeper measurement depth at a particular wavelength. The measurement depth is also influenced fairly by the absorption coefficient of the tissue. The larger absorption coefficient results in a shallower measurement depth. CONCLUSION: The correlations between the water contents measured by the optical and capacitance techniques were discussed. The dependencies of the light penetration depth on the source-detector geometry and wavelength are presented.     

Estimation of water content distribution in the skin using dualband polarization imaging

BACKGROUND/PURPOSE: A new enhancement imaging technique for visualizing two-dimensional distribution of water content in human tissue is proposed based on optical properties such as reflectance spectra and the scattering from the skin surface. METHODS: The method consists of two fundamental functions: spectral filtering for estimating skin hydration and polarization control for the appropriate measurement depth. Spectral filtering is simply achieved by utilizing the bandpass filters, whereas the measurement depth control is performed by changing the polarization directions in front of a light source and a detector. RESULTS: The combined method of spectral filtering and polarization imaging effectively visualized the water content distribution in skin as a shading on a composed black and white image. The result was compared with the measured value of the capacitance method, and the result of the proposed method was validated. CONCLUSION: Our results suggest that the proposed method enhances the scattering property in the skin according to the water content. Detailed discussions are given.     

A new approach for an estimation of the equilibrium stratum corneum water content

Background/purpose: Water content is the most vital parameter governing the overall function of the epidermal stratum corneum (SC). Thus, knowledge of the in vivo absolute water content of the SC is of great interest. Methods: We have investigated a non‐invasive method for the estimation of in vivo SC water content based on transepidermal water loss measurements combined with desorption studies of SC in vitro, by means of a dynamic vapour sorption setup where relative humidity (RH) and temperature are controlled. Results: The SC equilibrium water content of the volar forearm in our study was estimated to be 80±7 μg/cm². The estimate of the water content seems to decrease slightly with increasing ambient RH. Conclusion: The estimated water content is a bit lower than what can be expected to be realistic. A calibration against ambient RH is most probably needed if our method is to be applied over a broad range of values of the RH in the ambient air.     

Hydrophilic and lipophilic moisturizers have similar penetration profiles but different effects on SC water distribution in vivo

Abstract:  Dry skin is often treated with hydrophilic and/or lipophilic moisturizers. Hydrophilic moisturizers must penetrate the stratum corneum (SC) deeply to function properly, whereas lipophilic moisturizers should remain in the upper SC layers. In this study, both types of moisturizers were applied on volunteers for 3 h, after which the relative amount of moisturizer and the water distribution in the SC were determined using attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy in combination with tape-stripping. The results show that while hydrophilic moisturizers penetrate much more readily than lipophilic moisturizers, the latter are abundantly present in the upper regions of the SC. It was also observed that a 3-h treatment with lipophilic moisturizer did not result in increased water levels in the SC, whereas hydrophilic moisturizers retained water where they are located. The results suggest that upon prolonged application, adequate amounts of moisturizer can be obtained in those regions where they may cause moisturization in the central part of the SC. However, a single application of 3 h is probably too short to exert increased hydration as measured with ATR-FTIR.     

Free residual chlorine in bathing water reduces the water-holding capacity of the stratum corneum in atopic skin

Some patients with atopic dermatitis (AD) develop dry skin or exacerbated cutaneous inflammations with frequent swimming in public pools or after bathing. We examined the effects of residual chlorine in bathing water on the function of the stratum corneum (SC) in patients with AD and determined the lowest chlorine concentration showing an effect. In addition, we investigated the relationship between the free residual chlorine concentration in bathing water and the water-holding capacity of the SC in patients with AD. Twenty patients with AD and 10 normal control (NC) subjects were included in this study. The hydration status of the SC on the flexor surface of the forearm was measured with a corneometer before and after the subject's arms were immersed in tubs filled with comfortably hot water (40 degrees C) containing residual chlorine at concentrations of 0, 0.5, 1.0 and 2.0 mg/L for 10 minutes in a room maintained at normal temperature (24 degrees C) and relative humidity (55%). The water-holding capacity of the SC after immersion was calculated by integration of the hydration status determined every 30 seconds over a period of 10 minutes. In the patients with AD, the average SC hydration status after immersion in comfortably hot water containing residual chlorine at 1.0 and 2.0 mg/L was significantly lower than that following immersion in water containing a negligible concentration of residual chlorine (i.e., less than 0.03 mg/L) (p<0.05). In the NC subjects, significant differences were observed only between the 2.0 mg/L and the negligible residual chlorine groups (p<0.05). The water-holding capacity of the SC was significantly decreased with a residual chlorine concentration of 0.5 mg/L or higher in the patients with AD (p<0.01). However, in the NC subjects, a significant decrease in water-holding capacity was observed only at a residual chlorine concentration of 2 mg/L (p<0.01). These results indicate, first, that the water-holding capacity of the SC in patients with AD is more sensitive to free residual chlorine exposure than that in NC subjects without AD. Second, these results suggest that free residual chlorine exposure in patients with AD may play a role in the development or exacerbation of AD.     

Assessment of spray application of Saint GERVAIS® water effects on skin wettability by contact angle measurement comparison with bidistilled water

BACKGROUND: The skin is responsible for protecting the body from physical, chemical and microbial injuries. The stratum corneum is the top layer of the epidermis and it plays a key role in helping to contain moisture. When the skin becomes damaged, its ability to perform these functions is compromised. Dry skin is a common form of skin damage.Contact angle 0 between a surface and water is a good indicator of hydrophobic or hydrophilic tendency of surfaces. OBJECTIVE: To quantify the influence of spray application of an isotonic mineral water (Saint GERVAIS water) on the hydrophobic tendency of dry skin and to compare spreading of both types of water on the skin through 0 measurement of each water drop on the skin before and after mineral spray application. MATERIALS AND METHODS: Contact angles theta between skin surface and the two types of water (bidistilled and mineral water) were measured before and after application of mineral water by a system allowing the measurement of theta in vivo and in vitro. The cutaneous hydration, the temperature and pH were also measured before and after mineral water application. RESULTS: As for the application of mineral water, the cutaneous pH significantly increased so the strong skin acidity decreased. The cutaneous temperature was modified (a decrease of 2 degrees C was noted) and the cutaneous hydration was also increased (+47AU). The hydro-phobic tendency of the dry skin tested in this study was strongly decreased after mineral water application. This parameter was illustrated by a decrease of contact angle theta value. CONCLUSION: Saint GERVAIS water application allowed a regulation of skin pH, a fresh sensation on the skin and an increase in the cutaneous hydration. Moreover, the contact angle measurement with bidistilled water illustrated the increased wettability of the skin.     

International guidelines for the in vivo assessment of skin properties in non‐clinical settings: Part 2. transepidermal water loss and skin hydration

Background

There is an emerging perspective that it is not sufficient to just assess skin exposure to physical and chemical stressors in workplaces, but that it is also important to assess the condition, i.e. skin barrier function of the exposed skin at the time of exposure. The workplace environment, representing a non‐clinical environment, can be highly variable and difficult to control, thereby presenting unique measurement challenges not typically encountered in clinical settings.

Methods

An expert working group convened a workshop as part of the 5th International Conference on Occupational and Environmental Exposure of Skin to Chemicals (OEESC) to develop basic guidelines and best practices (based on existing clinical guidelines, published data, and own experiences) for the in vivo measurement of transepidermal water loss (TEWL) and skin hydration in non‐clinical settings with specific reference to the workplace as a worst‐case scenario.

Results

Key elements of these guidelines are: (i) to minimize or recognize, to the extent feasible, the influences of relevant endogenous‐, exogenous‐, environmental‐ and measurement/instrumentation‐related factors; (ii) to measure TEWL with a closed‐chamber type instrument; (iii) report results as a difference or percent change (rather than absolute values); and (iv) accurately report any notable deviations from this guidelines.

Conclusion

It is anticipated that these guidelines will promote consistent data reporting, which will facilitate inter‐comparison of study results.     

Mechanism of pajama material on stratum corneum water content under mild cold conditions: explored by hierarchical linear regression

OBJECTIVE: The aim of this study was to explore the effect of fabric material worn during nocturnal sleep on stratum corneum water content (SCWC) under mild cold conditions. METHOD: A controlled cross-over study has been designed to investigate systematically the effects of two kinds of pajama materials, cotton and polyester, on SCWC. Factors such as pajama fabric material, subjective perception and sleep quality were examined. Hierarchical linear regression was applied to assess the association between the factors and SCWC. RESULTS: Fabric material and subjective perception of coldness significantly predicted SCWC in the wear trial. Polyester fabric had a negative effect on SCWC compared with cotton, and subjective perception of coldness also had a negative effect on SCWC. CONCLUSION: The mechanisms by which pajama fabrics affect the SCWC could be due to the different thermal/hygroscopicity properties of the polyester and cotton fabric and the integral involvement of physiological and neurophysiological processes.     

In vivo simultaneous measurement of urea and water in the human stratum corneum by diffuse-reflectance near-infrared spectroscopy

Background/purpose: As near-infrared spectroscopy is a powerful non-invasive technique, information about several functional groups such as OH, NH, and CH can be monitored simultaneously. This study aimed to coincidentally measure urea and water contents in the human stratum corneum after the treatment of urea-containing cream, in vivo , by a Fourier transform near-infrared spectrometer with a fiber-optic probe.
Method: Diffuse reflectance spectra of heels of five healthy Japanese volunteers in the 1250–2500 nm region were measured in vivo before and after the 2-h treatment of urea-containing cream. The relative urea content of the heel was calculated from the peak height ratio at 1976 and 2175 nm in the second derivative spectra and that of water was obtained from the 1900 nm water band and that at 2175 nm. Water mobility was calculated from the peak top wavelength of the 1900 nm water band.
Results: The estimated water content tended to increase 1 and 2 h after the treatment compared with before the treatment and subsequently gradually decreased with time. The estimated urea content significantly increased 1 h after the treatment. Significant changes in peak wavelength to shorter wavelengths 1, 2, and 4 h after the treatment was observed, suggesting that the water mobility increased.
Conclusion: The estimated urea and water contents in heels before and after the treatment with urea-containing cream were monitored separately in vivo by diffuse reflectance near-infrared spectroscopy. We demonstrated the potential of NIR spectroscopy for evaluating the efficacy of topical application of a urea-containing cream to the skin in vivo .     

Analysis of human face skin surface molecules in situ by Fourier‐transform infrared spectroscopy

Background/purpose: For medical and dermatological researchers, it is important to realize the molecular dynamics and its control in the stratum corneum (SC) of human skin, which may be related to some skin abnormalities such as atopic dermatitis and skin pruritus. We have tried to analyze the periodic molecular dynamics of the outermost layers of SC in vivo. Methods: We measured the skin surface molecules of human face in situ non‐invasively using a Fourier‐transform infrared (FTIR) spectroscopy system attached with a newly designed attenuated total reflection (ATR) probe. The water‐extracted components from the SC were also analyzed using mass spectrometry, an enzymatic assay and high‐performance liquid chromatography characterization. Results: The infrared spectral changes of some components on the face skin at around 1000–1200 cm^?1 with circa‐monthly rhythms were observed when monitored for 10 months, and the components also showed a seasonal change. The analysis of different FTIR spectrum of the changeable components with circa‐monthly rhythm suggested the presence of a lactate compound. The presence of magnesium lactate in a conjugated form was detected in the water extract of SC. Conclusion: We demonstrate that the periodically changed components of the human face skin contained magnesium lactate conjugate as a major component.     

Nanoscale infrared (IR) spectroscopy and imaging of structural lipids in human stratum corneum using an atomic force microscope to directly detect absorbed light from a tunable IR laser source

An atomic force microscope (AFM) and a tunable infrared (IR) laser source have been combined in a single instrument (AFM‐IR) capable of producing ~200‐nm spatial resolution IR spectra and absorption images. This new capability enables IR spectroscopic characterization of human stratum corneum at unprecendented levels. Samples of normal and delipidized stratum corneum were embedded, cross‐sectioned and mounted on ZnSe prisms. A pulsed tunable IR laser source produces thermomechanical expansion upon absorption, which is detected through excitation of contact resonance modes in the AFM cantilever. In addition to reducing the total lipid content, the delipidization process damages the stratum corneum morphological structure. The delipidized stratum corneum shows substantially less long‐chain CH₂‐stretching IR absorption band intensity than normal skin. AFM‐IR images that compare absorbances at 2930/cm (lipid) and 3290/cm (keratin) suggest that regions of higher lipid concentration are located at the perimeter of corneocytes in the normal stratum corneum.     

Development and validation of a semiautomatic image analysis system for measuring skin desquamation with D-Squames®

Background D-Squames^®, have gained wide acceptance for assessing skin desquamation. The amount of corneocytes adhering to D-Squames^® can be assessed visually by trained observers or by computerized image analysis. Different image analysis algorythms for the evaluation of D-Squames^® have been published but have not been compared with each other. It was our aim to develop an image analysis system that does not require an expensive image analysis programming tool but should be optimized for routine tasks of analysing large numbers of samples. A second objective of this study was to compare two published image analysis algorythms and visual grading. Material and Methods The hardware components of the system are a CCD camera connected to a frame grabber card and a light box equipped with fluorescent tubes on two sides that provide a relatively cool, diffuse and even illumination of the sample. The following features were included into the software: generation and identification of bar codes for sample identification; semiautomatic recognition of ROI (region of interest), integration of study design into the analysing process, rapid calculation of desquamation index (DI: integration of the per cent area covered by scales and their thickness distribution) and/or scaling index (SI: distribution of grey values), data storage and export for further analysis. In a first step the system was validated by examining D-Squames covering a wide range of desquamation, by examining different ROI shapes (circle and square), by performing repeat measurements with different positions of the samples and by repeat measurements after re-callibrating the system. In a second step the effect of treatment with different moisturizers was evaluated by the two image analysis parameters DI and SI and compared with hydration measurements (Corneometer^®). Results The shape of the ROI showed no influence on the results (variability < 5%). Reproducibility of measurements was satisfactory (COV CDI): 1.7%, COV (SI): 2.6%).There was a good correlation between image analysis results and visual evaluation (means of 3 technicians) (r = 0.986) as well as between the two different image analysis parameters DI and SI (r = 0.971). In the clinical study moisturizer treatment resulted in variable reduction of desquamation that was closely correlated with increase in stratum corneum hydration (r = 0.97). Conclusion Analysing D-Squames^® with the image analysis system proved to be reproducible, independent of the shape of ROI, cost effective and fast and easy to operate. It has shown to be a suitable and reliable method for the objective determination of desquamation levels.     

Hydrating effect of potassium lactate is caused by increasing the interaction between water molecules and the serine residue of the stratum corneum protein

Natural moisturizing factors (NMFs) play an important role in maintaining the physical properties of the stratum corneum (SC). The relationship between SC water content and NMFs has long been investigated. Recently, we demonstrated that potassium lactate as an NMF increased SC water content more than sodium lactate did. The details of the moisturizing mechanism of NMFs, however, were not revealed. We, therefore, investigated the cause of the SC moisturizing effect of potassium lactate in comparison with sodium lactate. Using differential scanning calorimetry, we found that potassium lactate increased the bound water content of plantar SC more than what sodium lactate did. We also found, however, that the bound water content of the potassium lactate solution was less than that of the sodium lactate solution, suggesting that potassium lactate increased the water molecules interacting with SC components. Moreover, potassium lactate increased the ratio of hydrogen/deuterium exchange at 1340/cm, which represents the OH bending mode, of plantar SC spectra obtained by the attenuated total reflectance infrared spectroscopy. We assign this band to the OH group of the serine residue. These results suggest that potassium lactate increases the water-holding capacity of the SC by increasing interaction between water molecules and the OH group of serine in SC keratin.     

Skin hydration and transepidermal water loss in patients with a history of sulfur mustard contact: a case–control study

Background   Skin lesions are among the most common complications of contact with sulfur mustard.
Objective   This study was aimed to measure skin water content and transepidermal water loss (TEWL) in patients with a history of sulfur mustard contact.
Methods   Three hundred ten male participants were included in this study: 87 (28.1%) sulfur mustard–exposed patients with current skin lesions (group 1), 71 (22.9%) sulfur mustard–exposed patients without skin lesions (group 2), 78 (25.2%) patients with dermatitis (group 3) and 74 (23.8%) normal controls (group 4) The water content and TEWL of skin was measured at four different locations of the body: forehead, suprasternal, palm and dorsum of hand. Nonparametric statistical tests (Kruskal–Wallis) were used to compare the four groups, and P  < 0.05 was considered statistically significant.
Results   The mean age of participants were 44.0 ± 6.7, 41.9 ± 5.9, 43.8 ± 9.3 and 44.8 ± 8.9 years in groups 1 to 4, respectively ( P  = 0.146). Xerosis, post-lesional hyperpigmentation and lichenification were significantly more common in either sulfur mustard–exposed participants or non-exposed participants with dermatitis ( P  < 0.05). Skin hydration was higher in subjects with sulfur mustard contact than in non-injured participants ( P  < 0.05) in the dorsum and palm of hands and forehead. TEWL was significantly higher in participants only in suprasternal area and dorsum of hand.
Conclusion   Contact with sulfur mustard agent can alter biophysical properties of the skin-especially the function of stratum corneum as a barrier to water loss-several years after exposure.

Conflicts of interest

None declared.     

Measuring the effects of topical moisturizers on changes in stratum corneum thickness, water gradients and hydration in vivo

Background Moisturizers are the most commonly used topically applied product for the treatment of dry skin conditions. They affect many properties and functions of the stratum corneum but some moisturizers have been reported to be detrimental to barrier function. Stratum corneum barrier function is a composite of its total structure and thickness but few studies have taken this into account. As a biosensor, the stratum corneum (SC) will change its structure in response to treatment and a swelling effect has been clearly demonstrated by skin hydration. Recently several moisturizing agents have been shown to have an effect on SC swelling behaviour with conflicting results. However, there is a paucity of data reported for measuring the effects of long‐term usage of moisturizers on SC thickness in vivo as, until recently, traditional techniques did not have the resolution to measure the effects of moisturizers on nonpalmoplantar body sites. The development of confocal Raman spectroscopy for use in human subjects provides noninvasive, real‐time, in vivo measurement of SC water concentration profiles and we have also used this state of the art equipment to measure the effect of the long‐term use of moisturizers on SC thickness for the first time. Objectives To validate the use of confocal Raman spectroscopy (CRS) to measure SC thickness and then use it to investigate the short‐ and long‐term effects of moisturizers (one of which is known to improve SC barrier function) on SC thickness, water gradients and hydration. Methods Two studies were conducted: (i) to validate the use of CRS for measuring SC thickness through comparison with optical coherence tomography (OCT); and (ii) once validated to use CRS to measure the long‐term effects of three commercially available moisturizers (A, B, C) on SC thickness and water gradients, together with total hydration, over a 3‐week period (2 weeks of treatment and 1 week regression) and compare the spectroscopy‐derived hydration value with instrumentally derived capacitance hydration values. Results (i) A strong, positive correlation in SC thickness was obtained between CRS and OCT (OCT‐derived thickness = 0·96 × CRS‐derived thickness, r² = 0·93; P <0·0001). OCT was shown, however, to have a lower resolution than CRS in distinguishing SC thickness on thinner nonpalmoplantar body sites. Using the CRS method, differences in SC thickness were readily apparent on different body sites (cheek 12·8 ± 0·9 μm, volar forearm 18·0 ± 3·9 μm, leg 22·0 ± 6·9 μm). (ii) Examining the effects of moisturizers in a blinded, randomized 3‐week study in human volunteers (n = 14) demonstrated that only one commercially available formulation (A) changed SC water gradients, thickness and hydration as measured by CRS. These hydration data did not directly correlate with capacitance hydration values. Conclusions (i) In vivo CRS was validated as a technique to measure SC thickness on both palmoplantar and, particularly, on nonpalmoplantar skin sites. (ii) Moisturizers improve skin moisturization but in this study only formulation A improved SC thickness, water gradients and hydration as measured by CRS. We hypothesize that this was due to compositional differences between the products. We believe that niacinamide (nicotinamide, vitamin B₃) is probably contributing significantly to this effect, as it has been proven to increase epidermal lipogenesis and SC barrier function in other studies. These results show that by using CRS, we were able for the first time to determine the effect of moisturizer on multiple SC barrier endpoints including SC thickness, and water content as a function of depth and total SC water content.     

Circadian rhythms on skin function of hairless rats: light and thermic influences

Circadian rhythms are present in most functions of living beings. We have demonstrated the presence of circadian rhythms in skin variables (transepidermal water loss, TEWL; stratum corneum hydration, SCH; and skin temperature) in hairless rats under different environmental conditions of light and temperature. Circadian rhythms in TEWL and SCH showed mean amplitudes of about 20% and 14% around the mean, respectively, and appeared under light–dark cycles as well as under constant darkness. Environmental temperature was able to override TEWL, but not SCH rhythm, evidencing the dependency of TEWL on the temperature. Mean daily values of TEWL and SCH, and also the amplitude of TEWL rhythm, increased with the age of the animal. Under constant light, situation that induces arrhythmicity in rats, SCH and TEWL were inversely correlated. The results suggest the importance to take into account the functional skin rhythms in research in dermatological sciences.