Variable skin pH values are being reported in literature, all in the acidic range but with a broad range from pH 4.0 to 7.0. In a multicentre study (N = 330), we have assessed the skin surface pH of the volar forearm before and after refraining from showering and cosmetic product application for 24 h. The average pH dropped from 5.12 +/- 0.56 to 4.93 +/- 0.45. On the basis of this pH drop, it is estimated that the 'natural' skin surface pH is on average 4.7, i.e. below 5. This is in line with existing literature, where a relatively large number of reports (c. 50%) actually describes pH values below 5.0; this is in contrast to the general assumption, that skin surface pH is on average between 5.0 and 6.0. Not only prior use of cosmetic products, especially soaps, have profound influence on skin surface pH, but the use of plain tap water, in Europe with a pH value generally around 8.0, will increase skin pH up to 6 h after application before returning to its 'natural' value of on average below 5.0. It is demonstrated that skin with pH values below 5.0 is in a better condition than skin with pH values above 5.0, as shown by measuring the biophysical parameters of barrier function, moisturization and scaling. The effect of pH on adhesion of resident skin microflora was also assessed; an acid skin pH (4-4.5) keeps the resident bacterial flora attached to the skin, whereas an alkaline pH (8-9) promotes the dispersal from the skin.

Natural skin surface pH is on average below 5, which is beneficial for its resident flora

The ‘acid mantle’ of the stratum corneum seems to be important for both permeability barrier formation and cutaneous antimicrobial defense. However, the origin of the acidic pH, measurable on the skin

/pdf/the-ph-of-the-skin-surface-and-its-impact-on-the-barrier-ltokkf7h33.pdf

The pH of the skin surface and its impact on the barrier function.

Stratum corneum thickness was estimated from water concentration profiles of the skin measured by a confocal Raman spectrometer. Stratum corneum apparent thickness (SCAT) was defined as the depth where the water content reached an almost constant value. Site variations were determined using 15 healthy Japanese subjects (6 males, 9 females), and age variations at the cheek and forearm were examined using 27 female Japanese subjects. There were marked site variations in mean SCAT; 16.8 microm for cheek, 22.6 microm for volar forearm, 29.3 microm for back of the hand, and 173.0 microm for palm. These variations were similar to reported stratum corneum thickness values obtained in biopsy tissues. The SCAT tended to become age-dependently thicker at the forearm, but not at the cheek. In addition, SCAT was increased up to two-fold by hydration for 90 min, while lesser increases were seen with shorter hydration periods.

In vivo estimation of stratum corneum thickness from water concentration profiles obtained with Raman spectroscopy.

Provided herein are skin-mounted biomedical devices and methods of making and using biomedical devices for sensing and actuation applications. For example, flexible and/or stretchable biomedical devices are provided, including electronic devices useful for establishing conformal contact with the skin of a subject. Devices disclosed herein can comprise a plurality of sensing and/or actuating devices provided as part of a skin-mounted flexible or stretchable electronic circuit.

Flexible and Stretchable Electronic Systems for Epidermal Electronics

Substantial experimental evidence indicates that the hormonal form of vitamin D promotes the differentiation and inhibits the proliferation, invasiveness, and metastasis of human prostatic cancer cells. Results from epidemiologic studies of vitamin D status and/or vitamin D receptor (VDR) polymorphisms and prostate cancer risk have been mixed. We conducted a population-based, case-control study of advanced prostate cancer among men ages 40 to 79 years from the San Francisco Bay area. Interview data on lifetime sun exposure and other risk factors were collected for 905 non-Hispanic White men (450 cases and 455 controls). Using a reflectometer, we measured constitutive skin pigmentation on the upper underarm (a sun-protected site) and facultative pigmentation on the forehead (a sun-exposed site) and calculated a sun exposure index from these measurements. Biospecimens were collected for 426 cases and 440 controls. Genotyping was done for VDR polymorphisms in the 5' regulatory region (Cdx-2), exon 2 (FokI), and the 3' region (TaqI and BglI). Reduced risk of advanced prostate cancer was associated with high sun exposure determined by reflectometry [odds ratio (OR), 0.51; 95% confidence interval (95% CI), 0.33-0.80] and high occupational outdoor activity (OR, 0.73; 95% CI, 0.48-1.11). Significant risk reductions with the high-activity alleles FokI FF or Ff, TaqI tt, and BglI BB genotypes and a nonsignificant reduction with Cdx-2 AG or AA genotype were observed in the presence of high sun exposure, with ORs ranging from 0.46 to 0.67. Our findings support the hypothesis that sun exposure and VDR polymorphisms together play important roles in the etiology of prostate cancer.

https://cancerres.aacrjournals.org/content/canres/65/12/5470.full.pdf

Sun exposure, vitamin D receptor gene polymorphisms, and risk of advanced prostate cancer.

BACKGROUND/AIMS: Two types of skin reflectance instruments are available nowadays for the determination of skin color: a tristumulus colorimeter (Chromameter from Minolta) using the CIE L*a*b* color system and the narrow-band simple reflectance meters (DermaSpectrometer from Cortex and Mexameter from Courage-Khazaka) using the erythema/melanin indices. The purpose of this study was to compare the capabilities of the three instruments (sensitivity, repeatability and correlation) in vitro and in vivo. METHODS: Comparative color measurements were carried out first in vitro on standardized color charts and subsequently in vivo on different skin areas in human volunteers. Skin color changes induced by various physico-chemical treatments were also quantitatively evaluated with the three instruments. RESULTS: The in vitro and in vivo repeatabilty as well as the sensitivity of the three instruments are rather good. Erythema and skin blanching could be readily quantified by the increase of the a* parameter and of the erythema indices of the simple reflectance meters. Natural UV tanning and artificial chemical tanning could be measured by the decrease of L* and increase of b* and of the melanin indices. CONCLUSION: The Chromameter and the two narrow-band reflectance instruments were able to characterize skin color and to quantify small skin color changes. Moderate to high significant linear correlations could be established between the CIE L*a*b* color parameters and the erythema/melanin indices.

Skin color measurements: comparison between three instruments: the Chromameter®, the DermaSpectrometer® and the Mexameter®

Background/aims: A major problem with electrical measurements of the capacitance of the skin using the well kwown capacitance method (Corneometer) resides in the fact that the results of this instrument are expressed as arbitrary capacitance hydration units that are not directly related to real electrical units or to the water content of the horny layer. The purpose of this study was to establish a calibration of the capacitance method using a simple in vitro simulation system of the horny layer. Methods: The calibration of capacitance and conductance methods was carried out using cellulose filter papers saturated with water, aqueous solutions and liquids of different dielectric constant (sorption and desorption experiments). Results: Using this in vitro method, correlations were established between the capacitance values and the quantity of water adsorbed on the filter and with the dielectric constant of the liquid saturating the filter paper. High correlations were observed during sorption and desorption experiments between the capacitance and conductance measurements. Conclusions: In vitro calibration of the capacitance method is now possible with this simulation model of the horny layer. Furthermore, determination of the range of sensitivity, accuracy, repeatability and depth of detection of the measuring probe of the capacitance and conductance method were carried out.

In vitro calibration of the capacitance method (Corneometer CM 825) and conductance method (Skicon-200) for the evaluation of the hydration state of the skin.

Background/aims:
Some electrical properties of the skin may be related to the water content of the horny layer, and measurements of impedance and/or capacitance have been used to assess the hydration state of the skin surface. This study was designed to compare three commercially available instruments used in dermato-cosmetic research, namely, the Corneometer CM 825, the Nova DPM 9003 and the Skicon-200.

Methods:
Comparative measurements were carried out with the three instruments in vivo on the volar part of the forearms of 12 human volunteers.

Results:
The decrease in hydration induced by an irritant cationic detergent, and the increase of hydration after application of a moisturizer cream under occlusion could be easily measured with the three instruments. High degrees of correlation were obsewed between the three instruments over a broad range of hydration values of the skin.

Conclusions:
This comparative study performed under controlled environmental conditions reveals that the three instruments give validated coherent information concerning relative changes in hydration of the upper layers of the epidermis.

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®

Background/aims: The skin irritation potential of a body cleansing product is often compared under exaggerated test conditions, although the product is intended to be used at home with repetitive and brief contact with the skin. The aim of this study was to determine how much patch testing is predictive of the clinical, sub-clinical and subjective cutaneous effects of products used at home by consumers for their normal hygienic cleansing. Methods: A double-blind comparative study of the normal use of an alkaline soap bar and a syndet at home during 10 consecutive weeks was performed on two identical groups of 25 healthy female subjects. The eventual skin changes observed at different anatomical skin sites were evaluated by clinical visual examination and by bioengineering measurements before the start of the study and then every 2 weeks. The objective measurements were compared with the subject’s perceptions of dryness, tightness and product irritancy during the testing. Results: The bioengineering measurements did not show any significant changes on all the anatomical skin sites, except for a

https://www.healthmegamall.com/Articles/BabeskinArticle189.pdf

A comparative study of the effects on the skin of a classical bar soap and a syndet cleansing bar in normal use conditions and in the soap chamber test.

Background/aims: It was the aim of this study to carry out a comparative evaluation in vitro on standardized color charts and in vivo on healthy subjects using the Visi-Chroma VC-100®, a new imaging tristimulus colorimeter and the Minolta Chromameter CR-200® as a reference instrument. The Visi-Chroma combines tristimulus color analysis with full color visualization of the skin area measured. The technical performances of both instruments were compared with the purpose of validating the use of this new imaging colorimeter in dermatocosmetic research. Methods: In vitro L*a*b* color parameters were taken with both instruments on standardized color charts (Macbeth and RAL charts) in order to evaluate accuracy, sensitivity range and repeatability. These measurements were completed by in vivo studies on different sites of human skin and studies of color changes induced by topical chemical agents on forearm skin. The accuracy, sensitivity range and repeatability of measurements of selected distances and surfaces in the measuring zone considered and specific color determinations of specific skin zones were also determined. Results: The technical performance of this imaging colorimeter was rather good, with low coefficients of variation for repeatability of in vitro and vivo color measurements. High positive correlations were established in vitro and in vivo over a wide range of color measurements. The imaging colorimeter was able to measure the L*a*b* color parameters of specific chosen parts of the skin area considered and to measure accurately selected distances and surfaces in the same skin site considered. Conclusion: These comparative measurements show that both instruments have very similar technical performances and that high levels of correlation were obtained in vitro and in vivo using the L*a*b* color parameters. In addition, the Visi-Chroma presents the following improvements: 1) direct visualization and recording of the skin area considered with concomitant color measurements; 2) determination of the specific color parameters of skin areas chosen in the total measuring area; and 3) accurate determination of selected distances and surfaces in the same skin areas chosen.

André Barel

Papers

Skin color measurements: comparison between three instruments: the Chromameter®, the DermaSpectrometer® and the Mexameter®

In vitro calibration of the capacitance method (Corneometer CM 825) and conductance method (Skicon-200) for the evaluation of the hydration state of the skin.

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®

A comparative study of the effects on the skin of a classical bar soap and a syndet cleansing bar in normal use conditions and in the soap chamber test.

The Visi-Chroma VC-100: a new imaging colorimeter for dermatocosmetic research.