Accepted Article
Article Type : Original Article
Facial skin pigmentation is not related to stratum corneum cohesion, basal transepidermal water loss, barrier integrity and barrier repair
Author’s names: Rainer Voegeli1, Anthony V. Rawlings2, Beverley Summers3. Institutions and addresses: 1) DSM Nutritional Products Ltd., P.O. Box 2676, Bldg. 203.4/86, 4002 Basel, Switzerland Phone: +41 61 815 92 98 Fax: +41 61 815 80 50 Email: [email protected] 2) AVR Consulting Ltd, 26 Shavington Way, Kingsmead, Northwich, Cheshire CW9 8FH, United Kingdom Phone: +44 1606 354 535 Email: [email protected] 3) University of Limpopo, Medunsa Campus, Department of Pharmacy, PO Box 218, Medunsa 0204, South Africa Phone: +27 12 521 4673 Email: [email protected] Presentation of the paper: The paper has been presented at the Stratum Corneum VIII Conference (September 16-18, 2014, Cardiff).
ABSTRACT OBJECTIVE: Hypotheses have been developed for the evolutionary selection of skin pigmentation one of which relates to improved skin barrier function. The aim of this study was to compare facial skin condition on photoexposed (cheek) and photoprotected (postauricular) sites of naturally pigmented subjects of different ethnicities (Fitzpatrick skin phototypes II/III and V/VI) and Albino African subjects to understand better the relationship
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process which may lead to differences between this version and the Version of Record. Please cite this article as an 'Accepted Article', doi: 10.1111/ics.12189 This article is protected by copyright. All rights reserved.
Accepted Article
between facial stratum corneum (SC) barrier function, skin surface pH and skin pigmentation.
METHODS: Expert grading of skin conditions, skin surface pH and skin barrier function measurements were performed. For the latter, transepidermal water loss (TEWL) measurements before (basal TEWL), after 3, 6 and 9 consecutive tape strippings (SC integrity) and 3.5 h and 24 h post tape stripping (barrier recovery) were taken. Amounts of SC protein removed during stripping were estimated using infrared densitometry (SC cohesion).
RESULTS: Firstly, correlation analysis of the biometric data of the healthy Black African and Caucasian subjects showed there to be no relationship between pH and ITA° values nor pH & ITA° with basal TEWL, on the cheek. Neither skin pH nor ITA° correlated with integrity and recovery measurements, but skin pH correlated with SC cohesion. ITA° values were correlated with skin hydration. Secondly, on comparing the three ethnic groups, severe skin photodamage was observed in the Albino African subjects and their SC thickness was thicker. Whereas their basal TEWL was elevated, superior values for SC integrity, and barrier recovery were measured on the cheek sites. No differences in basal TEWL, SC integrity and barrier recovery were found between the other two subject groups. Equally, SC cohesion and skin surface pH values were similar among the three groups.
CONCLUSION: There was no relationship between ITA° values and basal TEWL, integrity, cohesion and recovery, but ITA° was correlated to skin hydration. Skin pH, irrespective of ITA° values correlated with SC cohesion, indicating a greater intracorneal cohesion at lower pH values.
This article is protected by copyright. All rights reserved.
Accepted Article
and 35 ± 10 % relative humidity. The study was conducted over a two week period when the weather was stable so climate-induced changes in barrier function could be excluded. All subjects participated in all stages of the study. There were not any dropouts. A correlation analysis of skin parameters was performed (Table I) followed by group analysis of the three ethnic groups (Table II)
Expert grading and quality of life questionnaire. Expert grading of facial dryness, roughness and erythema were scored according to a five point scale ranging from 0 to 4 (Table III) and facial photoaging was scored according to the four point Glogau’s scale (Table 2) [28-29]. Facial photography was performed using the Visia-CR imaging system (Canfield, Fairfield, NJ, USA). Subjects completed with the help of a trained technician a life style questionnaire, a modified Skindex-17 questionnaire and a questionnaire on cosmetic product use (Table IIVa) [30-32].
Skin surface pH, hydration and barrier function assessments. The skin sites were marked with a surgical marker to ensure that the measurement probes and the tapes were consistently applied to the same area of the subjects faces and the biophysical measurements were performed on a particular subject at the same time each day, to minimize variations induced by the circadian rhythm (Day 0 and Day 1 after tape stripping the skin) [33-35].
SC capacitance was measured using a Corneometer CM825 (Courage & Khazaka, Colonge, Germany), pH with a Skin-pH-Meter® PH 905 (Courage & Khazaka electronic, Cologne, Germany) and basal TEWL using an Aquaflux AF200 (Biox Systems, London, UK), on the photoexposed cheek and the photoprotected postauricular area of the right facial side as
This article is protected by copyright. All rights reserved.
Accepted Article
From the TEWL values and cumulative amount of SC proteins on tape strippings, the 1/TEWL vs. SCprotein
mass/area
(µgcm-2) was plotted. Fig. 5 shows the regressions for both
testing sites and between the different subject groups. The coefficient of determination between these parameters was not less than 0.97 indicating that there is a correlation between the skin barrier function and the total SCprotein mass/area. The X-intercept is indicative of SC thickness. As can be seen the SC is generally thinner on the cheek vs the postauricular site (on the cheek site the X-intercept was for the Albino Africans = 288, Black Africans = 213 and Caucasians = 172 and on the postauricular testing site for Albino Africans = 397, Black Africans = 248 and Caucasians = 258). The Albino African subjects had a significantly thicker SC by this estimate than the Black and Caucasian South African subjects irrespective of testing site (p≤0.001). However, the accumulated SC protein is similar for the Black African and the Caucasian subjects on the postauricular site but it is reduced for the Caucasian subjects on their cheeks but not statistically significant. This simple approach was considered sufficient to estimate the relative SC thicknesses between the subject groups. As can be seen on the photoprotected postauricular site the Albino African SC is approximately 60% thicker than the other two groups whereas it is approximately 67% thicker on the cheek compared with the Caucasian group and 35% thicker than the Black African subjects. The Black African SC is approximately 23% thicker on the cheek compared with the Caucasian group but not different on the postauricular site.
To further study, the possible differences in the SC barrier quality and its thickness we performed a linear mixed statistical model on the inverse TEWL values compared with cumulative SC protein. The absolute value of the slope is proportional to the barrier quality reflecting water transport resistance per unit SC thickness. There were no differences observed in the slope between the different testing sites similar to the basal TEWL values (Fig. 5). However, there were differences in the slope between the other two subject groups on either testing sites. The slope difference among the Albino Africans and the other two
This article is protected by copyright. All rights reserved.
Accepted Article
induced photodamage on the barrier. This complements the studies conducted on subjects living in the same geographical regions and at the same time allows an inter-ethnic comparison of facial SC barrier function (Caucasian South Africans and Black South Africans) together with an intra-ethnic comparison (amelanotic Albino South Africans and Black South Africans) to understand better the relationship between facial SC barrier function, skin surface pH, skin capacitance and skin pigmentation.
Materials and Methods. Study population and study set up. The study was a cross-sectional study and was approved from the School of Health Care Sciences Research and Ethics committee (SREC) together with the Medunsa Campus Research and Ethics Committee (MREC) and was conducted in accordance with the Declaration of Helsinki Principles. Written, informed consent was obtained from all participants before enrollment.
Sixty healthy female volunteers, living in Pretoria, South Africa participated in this observation which took place from end of November to early December 2013. There were three age-matched groups of Albino African, Black African and Caucasian subjects (Albino Africans aged 40.3 ± 2.9 yrs, Black Africans aged 38.2 ± 2.3 yrs and Caucasians aged 44.6 ± 3.1 yrs). Subjects did not apply any dermatological or cosmetic products to their faces for 3 days before expert grading and bioevaluation assessment of their facial skin. For the 3 day conditioning phase subjects cleansed the face with tepid water in the morning as well as in the afternoon. Before conducting the bio-instrumental measurements, the skin was cleaned by gentle swabbing with a cotton pad soaked with distilled water of ambient temperature and allowed to dry for 20 minutes. Subjects were acclimatized for 30 min before any measurements and measurements were performed in a room at a temperature of 21 ± 1 oC
This article is protected by copyright. All rights reserved.
Accepted Article
and 35 ± 10 % relative humidity. The study was conducted over a two week period when the weather was stable so climate-induced changes in barrier function could be excluded. All subjects participated in all stages of the study. There were not any dropouts. A correlation analysis of skin parameters was performed (Table I) followed by group analysis of the three ethnic groups (Table II)
Expert grading and quality of life questionnaire. Expert grading of facial dryness, roughness and erythema were scored according to a five point scale ranging from 0 to 4 (Table III) and facial photoaging was scored according to the four point Glogau’s scale (Table 2) [28-29]. Facial photography was performed using the Visia-CR imaging system (Canfield, Fairfield, NJ, USA). Subjects completed with the help of a trained technician a life style questionnaire, a modified Skindex-17 questionnaire and a questionnaire on cosmetic product use (Table IIVa) [30-32].
Skin surface pH, hydration and barrier function assessments. The skin sites were marked with a surgical marker to ensure that the measurement probes and the tapes were consistently applied to the same area of the subjects faces and the biophysical measurements were performed on a particular subject at the same time each day, to minimize variations induced by the circadian rhythm (Day 0 and Day 1 after tape stripping the skin) [33-35].
SC capacitance was measured using a Corneometer CM825 (Courage & Khazaka, Colonge, Germany), pH with a Skin-pH-Meter® PH 905 (Courage & Khazaka electronic, Cologne, Germany) and basal TEWL using an Aquaflux AF200 (Biox Systems, London, UK), on the photoexposed cheek and the photoprotected postauricular area of the right facial side as
This article is protected by copyright. All rights reserved.
Accepted Article This article is protected by copyright. All rights reserved.
Accepted Article
To evaluate the cohesion of the SC, the protein content of the tape strippings was quantified by infrared absorption measurements at 850 nm with SquameScanTM 850A (Heiland electronic, Wetzlar, Germany). For protein quantification the following equation was used:
CSC protein [μgcm-2] = 1.366 * absorption [%] – 1.557 [47-48].
To estimate the thickness of the SC, 1/TEWL was plotted versus the cumulative amount of tape stripped SC. According to Fick’s 1st Law of diffusion this should result in a straight line, assuming the macroarchitecture of the SC remains constant in depth. The intercept on the xaxis obtained by extrapolation is a measure for the dry SC mass per surface area which is related to SC thickness [46-49].
Statistics All data were collected in Microsoft Excel 2010 and checked for normality using the D’Agostino and Pearson omnibus normality test. In case of non-normality, data were either log transformed or non-parametric methodology was used. For parameters with measurements of two facial areas (cheek and postauricular), analyses were first performed for each area separately. To investigate whether there is a structural difference between the facial areas, data were then pooled and a joint (paired) analysis performed. Basal TEWL was log transformed and analysed with an ANOVA regarding the population group, followed by post-hoc Turkey tests. To investigate differences in facial areas, a linear mixed model was fit with group and facial area as fixed effects and subject as random effect (the interaction of facial area with population group was tested but not significant and thus removed). For the tape stripping challenge phase, which included basal TEWL measurements, a linear mixed model on log transformed TEWL values was fitted. This model included group, time and its interaction as fixed effects and a random intercept and
This article is protected by copyright. All rights reserved.
Accepted Article
slope over time for each individual. Time was included as a continuous variable and the log transformed basal TEWL was included as adjusting covariate. Pairwise group comparisons were performed with a Turkey adjustment. To investigate differences in facial areas, an extended model was fit, additionally including facial area and all resulting interactions as fixed effects. For barrier recovery, skin surface pH measurements, expert grading and analysis of the modified Skindex-17 questionnaire nonparametric Kruskal-Wallis tests were performed to detect differences across groups and pairwise comparisons via the Wilcoxon rank sum test were performed. To adjust for multiple comparisons, a Bonferroni adjustment was used. The difference in barrier recovery regarding facial area was further investigated applying Wilcoxon signed rank tests within each group. Inverse TEWL values and their relationship to cumulative SC protein were investigated using a linear mixed model with group, cumulative SC protein and its interaction as fixed effects and baseline SC protein as a continuous covariate. For each individual a random intercept and slope was included, and pairwise comparisons were performed with a Turkey adjustment To investigate differences in facial areas, an extended model was fit, additionally including facial area and all resulting 2way interactions as fixed effects. Cumulative SC protein and SC hydration were analysed with an ANOVA regarding the population group, followed by post-hoc Turkey tests. To investigate differences in facial areas, a linear mixed model was fit, including group and facial area as fixed effects. Statistical significance was set at α = 0.05. All analyses were performed with the statistical software R ([1], version 3.0.2) using the additional packages nlme ([2], version 3.1-113) and multcomp ([3], version 1.3-3) [50-52].
Results. Firstly to determine if there were any relationships between skin surface pH values, skin ITA° values and the biometric parameters measured (basal TEWL, skin capacitance, SC integrity, cohesion and recovery) linear regression and correlations were performed in the healthy Black Africans and Caucasians. The Albino Affricans were not included in this
This article is protected by copyright. All rights reserved.
Accepted Article
comparison due to their excessive photodamage. As can be seen from Table I only skin surface pH values correlated with cohesion and ITA° with hydration. Skin surface pH values did not correlate with ITA° values indicating that there was no relationship between skin pigmentation and skin pH. Equally there was no relationship of skin pH and basal TEWL. The behavior of the SC was also similar with skin pigmentation in terms of integrity and cohesion. Except for skin hydration there was no impact of skin pigmentation on the parameters measured.
Next we compared the biometric data and the expert gradings of the Black African and Caucasian subjects with the Albino subjects (Table II & III). A selection of Albino African subjects showing increasing skin damage by actinic keratosis are shown in Fig. 1. As can be seen from Table III skin dryness, roughness and keratoses were all significantly greater in the Albino African subjects compared with the other two subject groups while the Black African and Caucasian subjects were similar on both testing sites. With regards to skin erythema, the Albino Africans had greater skin erythema compared with the Black African and Caucasian subjects whereas the Caucasian African subjects also had greater erythema compared with the Black African subjects. These results indicate that the Albino Africans are especially suffering from skin photodamage and the Caucasian subjects are somewhat compared with the Black African subjects.
As expected from the correlation analysis, when the subjects are analysed as ethnic groupings (Table II) there are very minordifferences in skin surface pH values.The Albino African subjects had a slightly higher pH value compared with the Caucasian subjects (delta pH = 0.26) and a trend of increasing pH compared with the Black African subjects (delta pH = 0.25). However, the differences in the pH values were not statistically different. In addition, there was no difference in the skin surface pH values between the Caucasian and Black Africans.
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Accepted Article
Generally, the Albino African subjects had the lowest skin capacitance values on both testing sites but they were not significantly different from the measurements of the Caucasian subjects. However, the Black Africans subjects possessed the higher skin capacitance values compared with the other two subject groups similar to the correlation results (Tables I & II).
Fig. 2 shows the basal TEWL values for the three subject groups. Whereas there was no significant differences between the Black African and Caucasian subjects the Albino African subjects had greatly elevated TEWL values on both sites. As can be seen from Fig. 3 TEWL increased for all three subject groups with increasing number of tape stripping but Albino African subject’s increased significantly less than Black Africans on both testing sites (p
Article Type : Original Article
Facial skin pigmentation is not related to stratum corneum cohesion, basal transepidermal water loss, barrier integrity and barrier repair
Author’s names: Rainer Voegeli1, Anthony V. Rawlings2, Beverley Summers3. Institutions and addresses: 1) DSM Nutritional Products Ltd., P.O. Box 2676, Bldg. 203.4/86, 4002 Basel, Switzerland Phone: +41 61 815 92 98 Fax: +41 61 815 80 50 Email: [email protected] 2) AVR Consulting Ltd, 26 Shavington Way, Kingsmead, Northwich, Cheshire CW9 8FH, United Kingdom Phone: +44 1606 354 535 Email: [email protected] 3) University of Limpopo, Medunsa Campus, Department of Pharmacy, PO Box 218, Medunsa 0204, South Africa Phone: +27 12 521 4673 Email: [email protected] Presentation of the paper: The paper has been presented at the Stratum Corneum VIII Conference (September 16-18, 2014, Cardiff).
ABSTRACT OBJECTIVE: Hypotheses have been developed for the evolutionary selection of skin pigmentation one of which relates to improved skin barrier function. The aim of this study was to compare facial skin condition on photoexposed (cheek) and photoprotected (postauricular) sites of naturally pigmented subjects of different ethnicities (Fitzpatrick skin phototypes II/III and V/VI) and Albino African subjects to understand better the relationship
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process which may lead to differences between this version and the Version of Record. Please cite this article as an 'Accepted Article', doi: 10.1111/ics.12189 This article is protected by copyright. All rights reserved.
Accepted Article
between facial stratum corneum (SC) barrier function, skin surface pH and skin pigmentation.
METHODS: Expert grading of skin conditions, skin surface pH and skin barrier function measurements were performed. For the latter, transepidermal water loss (TEWL) measurements before (basal TEWL), after 3, 6 and 9 consecutive tape strippings (SC integrity) and 3.5 h and 24 h post tape stripping (barrier recovery) were taken. Amounts of SC protein removed during stripping were estimated using infrared densitometry (SC cohesion).
RESULTS: Firstly, correlation analysis of the biometric data of the healthy Black African and Caucasian subjects showed there to be no relationship between pH and ITA° values nor pH & ITA° with basal TEWL, on the cheek. Neither skin pH nor ITA° correlated with integrity and recovery measurements, but skin pH correlated with SC cohesion. ITA° values were correlated with skin hydration. Secondly, on comparing the three ethnic groups, severe skin photodamage was observed in the Albino African subjects and their SC thickness was thicker. Whereas their basal TEWL was elevated, superior values for SC integrity, and barrier recovery were measured on the cheek sites. No differences in basal TEWL, SC integrity and barrier recovery were found between the other two subject groups. Equally, SC cohesion and skin surface pH values were similar among the three groups.
CONCLUSION: There was no relationship between ITA° values and basal TEWL, integrity, cohesion and recovery, but ITA° was correlated to skin hydration. Skin pH, irrespective of ITA° values correlated with SC cohesion, indicating a greater intracorneal cohesion at lower pH values.
This article is protected by copyright. All rights reserved.
Accepted Article
and 35 ± 10 % relative humidity. The study was conducted over a two week period when the weather was stable so climate-induced changes in barrier function could be excluded. All subjects participated in all stages of the study. There were not any dropouts. A correlation analysis of skin parameters was performed (Table I) followed by group analysis of the three ethnic groups (Table II)
Expert grading and quality of life questionnaire. Expert grading of facial dryness, roughness and erythema were scored according to a five point scale ranging from 0 to 4 (Table III) and facial photoaging was scored according to the four point Glogau’s scale (Table 2) [28-29]. Facial photography was performed using the Visia-CR imaging system (Canfield, Fairfield, NJ, USA). Subjects completed with the help of a trained technician a life style questionnaire, a modified Skindex-17 questionnaire and a questionnaire on cosmetic product use (Table IIVa) [30-32].
Skin surface pH, hydration and barrier function assessments. The skin sites were marked with a surgical marker to ensure that the measurement probes and the tapes were consistently applied to the same area of the subjects faces and the biophysical measurements were performed on a particular subject at the same time each day, to minimize variations induced by the circadian rhythm (Day 0 and Day 1 after tape stripping the skin) [33-35].
SC capacitance was measured using a Corneometer CM825 (Courage & Khazaka, Colonge, Germany), pH with a Skin-pH-Meter® PH 905 (Courage & Khazaka electronic, Cologne, Germany) and basal TEWL using an Aquaflux AF200 (Biox Systems, London, UK), on the photoexposed cheek and the photoprotected postauricular area of the right facial side as
This article is protected by copyright. All rights reserved.
Accepted Article
From the TEWL values and cumulative amount of SC proteins on tape strippings, the 1/TEWL vs. SCprotein
mass/area
(µgcm-2) was plotted. Fig. 5 shows the regressions for both
testing sites and between the different subject groups. The coefficient of determination between these parameters was not less than 0.97 indicating that there is a correlation between the skin barrier function and the total SCprotein mass/area. The X-intercept is indicative of SC thickness. As can be seen the SC is generally thinner on the cheek vs the postauricular site (on the cheek site the X-intercept was for the Albino Africans = 288, Black Africans = 213 and Caucasians = 172 and on the postauricular testing site for Albino Africans = 397, Black Africans = 248 and Caucasians = 258). The Albino African subjects had a significantly thicker SC by this estimate than the Black and Caucasian South African subjects irrespective of testing site (p≤0.001). However, the accumulated SC protein is similar for the Black African and the Caucasian subjects on the postauricular site but it is reduced for the Caucasian subjects on their cheeks but not statistically significant. This simple approach was considered sufficient to estimate the relative SC thicknesses between the subject groups. As can be seen on the photoprotected postauricular site the Albino African SC is approximately 60% thicker than the other two groups whereas it is approximately 67% thicker on the cheek compared with the Caucasian group and 35% thicker than the Black African subjects. The Black African SC is approximately 23% thicker on the cheek compared with the Caucasian group but not different on the postauricular site.
To further study, the possible differences in the SC barrier quality and its thickness we performed a linear mixed statistical model on the inverse TEWL values compared with cumulative SC protein. The absolute value of the slope is proportional to the barrier quality reflecting water transport resistance per unit SC thickness. There were no differences observed in the slope between the different testing sites similar to the basal TEWL values (Fig. 5). However, there were differences in the slope between the other two subject groups on either testing sites. The slope difference among the Albino Africans and the other two
This article is protected by copyright. All rights reserved.
Accepted Article
induced photodamage on the barrier. This complements the studies conducted on subjects living in the same geographical regions and at the same time allows an inter-ethnic comparison of facial SC barrier function (Caucasian South Africans and Black South Africans) together with an intra-ethnic comparison (amelanotic Albino South Africans and Black South Africans) to understand better the relationship between facial SC barrier function, skin surface pH, skin capacitance and skin pigmentation.
Materials and Methods. Study population and study set up. The study was a cross-sectional study and was approved from the School of Health Care Sciences Research and Ethics committee (SREC) together with the Medunsa Campus Research and Ethics Committee (MREC) and was conducted in accordance with the Declaration of Helsinki Principles. Written, informed consent was obtained from all participants before enrollment.
Sixty healthy female volunteers, living in Pretoria, South Africa participated in this observation which took place from end of November to early December 2013. There were three age-matched groups of Albino African, Black African and Caucasian subjects (Albino Africans aged 40.3 ± 2.9 yrs, Black Africans aged 38.2 ± 2.3 yrs and Caucasians aged 44.6 ± 3.1 yrs). Subjects did not apply any dermatological or cosmetic products to their faces for 3 days before expert grading and bioevaluation assessment of their facial skin. For the 3 day conditioning phase subjects cleansed the face with tepid water in the morning as well as in the afternoon. Before conducting the bio-instrumental measurements, the skin was cleaned by gentle swabbing with a cotton pad soaked with distilled water of ambient temperature and allowed to dry for 20 minutes. Subjects were acclimatized for 30 min before any measurements and measurements were performed in a room at a temperature of 21 ± 1 oC
This article is protected by copyright. All rights reserved.
Accepted Article
and 35 ± 10 % relative humidity. The study was conducted over a two week period when the weather was stable so climate-induced changes in barrier function could be excluded. All subjects participated in all stages of the study. There were not any dropouts. A correlation analysis of skin parameters was performed (Table I) followed by group analysis of the three ethnic groups (Table II)
Expert grading and quality of life questionnaire. Expert grading of facial dryness, roughness and erythema were scored according to a five point scale ranging from 0 to 4 (Table III) and facial photoaging was scored according to the four point Glogau’s scale (Table 2) [28-29]. Facial photography was performed using the Visia-CR imaging system (Canfield, Fairfield, NJ, USA). Subjects completed with the help of a trained technician a life style questionnaire, a modified Skindex-17 questionnaire and a questionnaire on cosmetic product use (Table IIVa) [30-32].
Skin surface pH, hydration and barrier function assessments. The skin sites were marked with a surgical marker to ensure that the measurement probes and the tapes were consistently applied to the same area of the subjects faces and the biophysical measurements were performed on a particular subject at the same time each day, to minimize variations induced by the circadian rhythm (Day 0 and Day 1 after tape stripping the skin) [33-35].
SC capacitance was measured using a Corneometer CM825 (Courage & Khazaka, Colonge, Germany), pH with a Skin-pH-Meter® PH 905 (Courage & Khazaka electronic, Cologne, Germany) and basal TEWL using an Aquaflux AF200 (Biox Systems, London, UK), on the photoexposed cheek and the photoprotected postauricular area of the right facial side as
This article is protected by copyright. All rights reserved.
Accepted Article This article is protected by copyright. All rights reserved.
Accepted Article
To evaluate the cohesion of the SC, the protein content of the tape strippings was quantified by infrared absorption measurements at 850 nm with SquameScanTM 850A (Heiland electronic, Wetzlar, Germany). For protein quantification the following equation was used:
CSC protein [μgcm-2] = 1.366 * absorption [%] – 1.557 [47-48].
To estimate the thickness of the SC, 1/TEWL was plotted versus the cumulative amount of tape stripped SC. According to Fick’s 1st Law of diffusion this should result in a straight line, assuming the macroarchitecture of the SC remains constant in depth. The intercept on the xaxis obtained by extrapolation is a measure for the dry SC mass per surface area which is related to SC thickness [46-49].
Statistics All data were collected in Microsoft Excel 2010 and checked for normality using the D’Agostino and Pearson omnibus normality test. In case of non-normality, data were either log transformed or non-parametric methodology was used. For parameters with measurements of two facial areas (cheek and postauricular), analyses were first performed for each area separately. To investigate whether there is a structural difference between the facial areas, data were then pooled and a joint (paired) analysis performed. Basal TEWL was log transformed and analysed with an ANOVA regarding the population group, followed by post-hoc Turkey tests. To investigate differences in facial areas, a linear mixed model was fit with group and facial area as fixed effects and subject as random effect (the interaction of facial area with population group was tested but not significant and thus removed). For the tape stripping challenge phase, which included basal TEWL measurements, a linear mixed model on log transformed TEWL values was fitted. This model included group, time and its interaction as fixed effects and a random intercept and
This article is protected by copyright. All rights reserved.
Accepted Article
slope over time for each individual. Time was included as a continuous variable and the log transformed basal TEWL was included as adjusting covariate. Pairwise group comparisons were performed with a Turkey adjustment. To investigate differences in facial areas, an extended model was fit, additionally including facial area and all resulting interactions as fixed effects. For barrier recovery, skin surface pH measurements, expert grading and analysis of the modified Skindex-17 questionnaire nonparametric Kruskal-Wallis tests were performed to detect differences across groups and pairwise comparisons via the Wilcoxon rank sum test were performed. To adjust for multiple comparisons, a Bonferroni adjustment was used. The difference in barrier recovery regarding facial area was further investigated applying Wilcoxon signed rank tests within each group. Inverse TEWL values and their relationship to cumulative SC protein were investigated using a linear mixed model with group, cumulative SC protein and its interaction as fixed effects and baseline SC protein as a continuous covariate. For each individual a random intercept and slope was included, and pairwise comparisons were performed with a Turkey adjustment To investigate differences in facial areas, an extended model was fit, additionally including facial area and all resulting 2way interactions as fixed effects. Cumulative SC protein and SC hydration were analysed with an ANOVA regarding the population group, followed by post-hoc Turkey tests. To investigate differences in facial areas, a linear mixed model was fit, including group and facial area as fixed effects. Statistical significance was set at α = 0.05. All analyses were performed with the statistical software R ([1], version 3.0.2) using the additional packages nlme ([2], version 3.1-113) and multcomp ([3], version 1.3-3) [50-52].
Results. Firstly to determine if there were any relationships between skin surface pH values, skin ITA° values and the biometric parameters measured (basal TEWL, skin capacitance, SC integrity, cohesion and recovery) linear regression and correlations were performed in the healthy Black Africans and Caucasians. The Albino Affricans were not included in this
This article is protected by copyright. All rights reserved.
Accepted Article
comparison due to their excessive photodamage. As can be seen from Table I only skin surface pH values correlated with cohesion and ITA° with hydration. Skin surface pH values did not correlate with ITA° values indicating that there was no relationship between skin pigmentation and skin pH. Equally there was no relationship of skin pH and basal TEWL. The behavior of the SC was also similar with skin pigmentation in terms of integrity and cohesion. Except for skin hydration there was no impact of skin pigmentation on the parameters measured.
Next we compared the biometric data and the expert gradings of the Black African and Caucasian subjects with the Albino subjects (Table II & III). A selection of Albino African subjects showing increasing skin damage by actinic keratosis are shown in Fig. 1. As can be seen from Table III skin dryness, roughness and keratoses were all significantly greater in the Albino African subjects compared with the other two subject groups while the Black African and Caucasian subjects were similar on both testing sites. With regards to skin erythema, the Albino Africans had greater skin erythema compared with the Black African and Caucasian subjects whereas the Caucasian African subjects also had greater erythema compared with the Black African subjects. These results indicate that the Albino Africans are especially suffering from skin photodamage and the Caucasian subjects are somewhat compared with the Black African subjects.
As expected from the correlation analysis, when the subjects are analysed as ethnic groupings (Table II) there are very minordifferences in skin surface pH values.The Albino African subjects had a slightly higher pH value compared with the Caucasian subjects (delta pH = 0.26) and a trend of increasing pH compared with the Black African subjects (delta pH = 0.25). However, the differences in the pH values were not statistically different. In addition, there was no difference in the skin surface pH values between the Caucasian and Black Africans.
This article is protected by copyright. All rights reserved.
Accepted Article
Generally, the Albino African subjects had the lowest skin capacitance values on both testing sites but they were not significantly different from the measurements of the Caucasian subjects. However, the Black Africans subjects possessed the higher skin capacitance values compared with the other two subject groups similar to the correlation results (Tables I & II).
Fig. 2 shows the basal TEWL values for the three subject groups. Whereas there was no significant differences between the Black African and Caucasian subjects the Albino African subjects had greatly elevated TEWL values on both sites. As can be seen from Fig. 3 TEWL increased for all three subject groups with increasing number of tape stripping but Albino African subject’s increased significantly less than Black Africans on both testing sites (p
