Epidermal Barrier Function and Skin Homeostasis in Atopic Dermatitis: The Impact of Age

  Citation: Montero-Vilchez, T.; Cuenca-Barrales, C.; Rodriguez-Pozo, J.-A.; Diaz-Calvillo, P.; Tercedor-Sanchez, J.; Martinez-Lopez, A.; Molina-Leyva, A.; Arias-Santiago, S. Epidermal Barrier Function and Skin Homeostasis in Atopic Dermatitis: The Impact of Age. Life 2022,12, 132. https:// doi.org/10.3390/life12010132 Academic Editors: Luis Monteiro Rodrigues, Bernard Querleux and Rolland Gyulai Received: 21 December 2021 Accepted: 15 January 2022 Published: 17 January 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). life Article Epidermal Barrier Function and Skin Homeostasis in Atopic Dermatitis: The Impact of Age Trinidad Montero-Vilchez 1,2,†, Carlos Cuenca-Barrales 1,2,† , Juan-Angel Rodriguez-Pozo 1, Pablo Diaz-Calvillo 1, Jesús Tercedor-Sanchez 1,2 , Antonio Martinez-Lopez 1,2, Alejandro Molina-Leyva 1,2,* and Salvador Arias-Santiago 1,2,3 1Dermatology Department, Hospital Universitario Virgen de las Nieves, Avenida de Madrid, 15, 18012 Granada, Spain; [email protected] (T.M.-V.); [email protected] (C.C.-B.); [email protected] (J.-A.R.-P.); [email protected] (P.D.-C.); [email protected] (J.T.-S.); [email protected] (A.M.-L.); [email protected] (S.A.-S.) 2Instituto de Investigación Biosanitaria Granada, 18012 Granada, Spain 3Dermatology Department, Faculty of Medicine, University of Granada, 18011 Granada, Spain *Correspondence: alejandr[email protected]; Tel.: +34-958-023-422 † These authors contributed equally to this work. Abstract: Skin is damaged in atopic dermatitis (AD) patients. Age is also believed to have a negative effect on epidermal barrier function. The aim of this study was to investigate skin barrier function changes with age in AD patients. A cross-sectional study was conducted including 162 participants, 81 AD patients and 81 healthy volunteers. Skin barrier function parameters, such as transepidermal water loss (TEWL), erythema, temperature, stratum corneum hydration (SCH), pH, and elasticity, were evaluated. Healthy volunteers were evaluated on the volar forearm. AD patients were measured on two regions: on an eczematous lesion on the volar forearm and on a non-involved area 5 cm from the affected area. TEWL was lower on healthy skin than uninvolved AD skin (9.98 vs. 25.51 g · m −2· h −1 ,p< 0.001) and AD eczematous lesions (9.98 vs. 28.38 g · m −2· h −1 ,p< 0.001). SCH was lower on AD eczematous lesions than uninvolved AD skin (24.23 vs. 39.36 AU, p< 0.001) and healthy skin (24.23 vs. 44.36 AU, p< 0.001). Elasticity was lower on AD eczematous lesions than uninvolved AD skin (0.69 vs. 0.74, p= 0.038) and healthy skin (0.69 vs. 0.77, p= 0.014). A negative correlation was found between age and elasticity in all the population (r = − 0.383, p< 0.001). This correlation was stronger in AD patients (r = − 0.494, p< 0.001) than in controls (r = − 0.266, p= 0.092). After conducting a linear regression model in AD patients adjusted by age, sex, and SCORing Atopic Dermatitis (SCORAD), it was found that elasticity was impaired by an increasing age ( β = − 0.004, p< 0.001) and a higher SCORAD ( β = − 0.003, p< 0.001). The skin barrier function is impaired by age and AD, reflected mainly in poor elasticity values in older AD patients. Keywords: aging; atopic dermatitis; skin barrier; stratum corneum 1. Introduction The skin is the human body’s largest organ. It accomplishes multiple defensive and regulatory functions as it protects the body against external stressors and maintains cutaneous homeostasis [ 1 ]. The skin barrier function resides mainly in the stratum corneum of the epidermis [ 2 ]. Transepidermal water loss (TEWL) evaluates the diffusion of condensed water through the stratum corneum and is a key characteristic of the skin barrier [ 3 ]. Greater TEWL is often associated with skin barrier impairment and has been observed in several skin diseases [ 4 , 5 ]. Stratum corneum hydration (SCH), the water content of the stratum corneum, is another important parameter, and a lower value is frequently associated with skin barrier dysfunction [ 6 ]. The skin surface pH is also considered in the assessment of epidermal functions, as high pH values are related to loss of antimicrobial activity [ 7 ]. Life 2022,12, 132. https://doi.org/10.3390/life12010132 https://www.mdpi.com/journal/life Life 2022,12, 132 2 of 14 Erythema is also useful in assessing the integrity of the epidermal barrier [ 8 ]. Elasticity is another important feature related to skin biomechanical properties [9]. Skin aging is an intrinsic and extrinsic process. Intrinsic, or chronologic aging, is an inevitable, genetically determined process. Histologically, the epidermis gets thinner, and the dermal-epidermal junction flattens, increasing skin fragility and decreasing nutrient transfer. Epidermal cell turnover decreases, slowing wound healing, and the dermis becomes atrophic with reduced numbers of fibroblasts and subdermal adipose tissue [10]. Moreover, the number and diameter of collagen fiber bundles decrease and the ratio of type III collagen to type I collagen increases [ 11 ]. Clinically, intrinsic aging is characterized by laxity and some exaggerated expression lines [ 12 ]. Extrinsic aging is associated with external factors, with sun exposure being the most deleterious. Histologically, photoaged skin is characterized by elastosis, an accumulation of elastin material below the dermalepidermal junction, epidermal atrophy, and fragmentation of collagen and elastic fibers. Clinically, it is reflected as dryness, wrinkles, irregular pigmentation, loss of elasticity, telangiectasias, and purpura [13]. Atopic dermatitis (AD) is a chronic cutaneous inflammatory disease caused by environmental and genetic factors. It is characterized by recurrent, eczematous lesions associated with pruritus [ 14 ]. Epidermal barrier dysfunction, immune dysregulation, and gut dysbiosis may play roles in this disease [15]. AD affects up to 20% of children and 10% of adults, with higher prevalence in industrialized countries [ 16 ]. Nevertheless, the incidence in adult patients is increasing due to an aging society and the accumulation of environmental stressors and their cumulative impact on epidermal barrier function [ 17 ]. There is scarce evidence regarding the differences between AD in children and adults [ 18 ]. Children compared with adults with AD showed decreased filaggrin expression and activation of T helper cells (Th)2, Th22, and Th1, and a higher induction of Th17-related cytokines, antimicrobials, Th9, interleukin (IL)-33, and innate markers [ 19 ]. Moreover, it was observed that IL-31 and IL-33 levels were higher in children than adults with AD, whereas thymic stromal lymphopoietin (TSLP) and immunoglobulin (Ig) E levels were similar in children and adults [ 20 ]. Nevertheless, we found no studies that evaluated the differences in epidermal barrier function between adults with AD younger and older than 30 years. Assessing skin homeostasis and epidermal barrier function in lesioned and non-lesioned skin would provide a better understanding of the complex pathogenesis of this disease [ 21 ], as well as would provide tools to assess disease severity objectively [5]. Skin aging shares some immunological findings with AD. Both Th1 and Th17 are increased with age and in AD patients. Nevertheless, Th2/Th22 and matrix metalloproteinase 12 (MMP-12) increase within normal aging while their levels are inversely correlated with age in the skin of older AD patients [ 22 , 23 ]. The terminal differentiation markers expression, such as filaggrin or loricrin, significantly increase with age in AD, while they decrease in endogenously aged skin [ 17 ]. Ki16 and Ki67, epidermal hyperplasia markers, are increased in atopic skin but they diminish in AD with age [ 24 ]. To date, the differences between endogenous skin aging and aging AD skin are not completely understood. The aim of this study is to investigate skin barrier function changes with age in AD patients, assessed by objective parameters including TEWL, SCH, erythema, temperature, pH and elasticity. 2. Materials and Methods A cross-sectional study was conducted. Participants were recruited from October 2020 to February 2021 in the Dermatology Service of the Hospital Universitario Virgen de las Nieves, Granada, Spain. Patients with an established clinical diagnosis of mild to severe AD [ 14 ] were included in the study. The diagnosis of AD was made by a dermatologist following Hanifin y Rajka criteria [ 14 , 25 ]. Healthy controls, volunteers who attended our Dermatology Department for common conditions, such as seborrheic keratoses or melanocytic nevi, and did not have previous family or personal history of any inflammatory skin disease were also included Life 2022,12, 132 3 of 14 in the study. The exclusion criteria were having a clinical infection on the measured area, history of cancer or not signing the informed consent form. Sociodemographic and clinical data were gathered by clinical interview and physical examination. Sex, age, smoking/alcohol habits, and emollient use were collected. The participants were classified according to their age: <30 years or ≥ 30 years, as the turning points of skin barrier function appears in an individual’s thirties [ 26 ]. AD severity was assessed by the SCORing Atopic Dermatitis (SCORAD), the Eczema Area Severity Index (EASI), and body surface area (BSA). Homeostatic parameters in relation to epidermal barrier function were evaluated on the volar forearm. AD patients were measured on an eczematous area on the volar forearm and on a non-involved area 5 cm from the affected area. Healthy volunteers were also measured on the volar forearm. TEWL (in g · m −2· h −1 , using Tewameter ® TM300, Mirocaya, Bilbao, Spain), pH (using Skin-pH-Meter ® PH905, Mirocaya, Bilbao, Spain), skin temperature (in ◦ C, using Skin-Thermometer ST 500, Mirocaya, Bilbao, Spain), erythema index (in arbitrary units (AU), using Mexameter ® MX 18, Mirocaya, Bilbao, Spain), SCH (in arbitrary units, using Corneometer ® CM825, Mirocaya, Bilbao, Spain), and elasticity parameters (including R2 value, measured in %, using Cutometer ® Dual MPA 580, Mirocaya, Bilbao, Spain) were measured by a Multi Probe Adapter (MPA, Courage + Khazaka electronic GmbH, Mirocaya, Bilbao, Spain). All these measurements were taken following the same order. The parameters were measured ten times and their average was used for analysis. All these measurements were taken in the same room at a mean room ambient air humidity of 45% (range, 40–50%) and temperature of 22 ± 1 ◦ C. All participants underwent an adaptation period of at least 20 min before the measurements were taken. Topical or systemic treatments were not allowed three hours before the measurements were taken. To perform the descriptive analysis, qualitative variables were expressed as absolute and relative frequency distributions and continuous variables as means ± standard deviations (SD). To compare continuous variables, the Student’s t-test for independent samples or Student’s t-test for paired samples were used, as appropriate. To test for possible correlations between continuous variables, the Pearson correlation coefficient was calculated. Linear regression models were used to evaluate factors associated with impaired cutaneous homeostasis. Statistical significance was defined by a two-tailed p< 0.05. SPSS version 24.0 (SPSS Inc., Chicago, IL, USA) was used for statistical analyses. This study was approved by the ethics committee of Hospital Universitario Virgen de las Nieves (Epidermal Barrier Function and Skin Homeostasis project). The nature of the study was explained to all the participants, who agreed to participate and signed their informed consent form. All measurements were non-invasive, and the confidentiality of participant data was strictly preserved. 3. Results This study included 162 participants, 81 patients with AD and 81 healthy volunteers with a mean age of 29.64 (16.71 SD) years, Figure 1. The sociodemographic characteristics of the sample are described in Table 1. AD patients had a mean EASI of 19.37 (8.59 SD) and a mean SCORAD of 40.98 (21.48 SD). Life 2022,12, 132 4 of 14 Life 2022, 12, x FOR PEER REVIEW 4 of 14 Figure 1. Age distribution in the population. Table 1. Characteristics of the sample. Sociodemographic Features Atopic Dermatitis Patients (n = 81) Healthy Participants (n = 81) p Value * Age (years) 31.88 (14.92) 27.40 (18.15) 0.088 Sex (%) 1.00 - Female 53 (65.4%) 53 (65.4%) - Male 28 (34.6%) 28 (34.6%) Smoking habit (yes) 14 (17.28%) 6 (7.4%) 0.291 Alcohol habit (yes) 26 (32.10%) 24 (29.63%) 0.873 Emollients use (yes) 68 (83.95%) 53 (65.43%) 0.080 Treatment - - - Topical treatment 45 (55.56%) - Systemic treatment 27 (33.33%) - Biologic drugs 9 (11.11%) Data are expressed as relative (absolute) frequencies and means (standard deviations (SDs)). * p value after using Student T test for independent samples to compare continuous variables and the chi-square test to compare categoric data between healthy participants and atopic dermatitis patients. Skin homeostasis parameters between healthy skin, uninvolved AD skin and AD eczematous lesions were compared (Figure 2, Table S1). TEWL was lower on healthy skin than uninvolved AD skin (9.98 vs. 25.51 g·m−2·h−1, p < 0.001) and AD eczematous lesions (9.98 vs. 28.38 g·m−2·h−1, p < 0.001), while no differences between uninvolved AD skin and AD eczematous lesion were found. SCH was lower on AD eczematous lesions than uninvolved AD skin (24.23 vs. 39.36 AU, p < 0.001) and healthy skin (24.23 vs. 44.36 AU, p < 0.001). Temperature was higher on AD eczematous lesions compared with uninvolved AD skin (32.07 vs. 31.28 °C, p < 0.001) and healthy skin (32.07 vs. 31.11 °C, p < 0.001). Erythema was higher on AD eczematous lesion than uninvolved AD skin (391.11 vs. 239.88 AU, p < 0.001) and healthy skin (391.11 vs. 218.93 AU, p < 0.001). pH was higher on AD eczematous lesions compared with healthy skin (6.15 vs. 5.92, p = 0.039). Elasticity was lower on AD eczematous lesions than uninvolved AD skin (0.69 vs. 0.74, p = 0.038) and healthy skin (0.69 vs. 0.77, p = 0.014). Figure 1. Age distribution in the population. Table 1. Characteristics of the sample. Sociodemographic Features Atopic Dermatitis Patients (n= 81) Healthy Participants (n= 81) pValue * Age (years) 31.88 (14.92) 27.40 (18.15) 0.088 Sex (%) 1.00 -Female 53 (65.4%) 53 (65.4%) -Male 28 (34.6%) 28 (34.6%) Smoking habit (yes) 14 (17.28%) 6 (7.4%) 0.291 Alcohol habit (yes) 26 (32.10%) 24 (29.63%) 0.873 Emollients use (yes) 68 (83.95%) 53 (65.43%) 0.080 Treatment - - -Topical treatment 45 (55.56%) -Systemic treatment 27 (33.33%) -Biologic drugs 9 (11.11%) Data are expressed as relative (absolute) frequencies and means (standard deviations (SDs)). * pvalue after using Student T test for independent samples to compare continuous variables and the chi-square test to compare categoric data between healthy participants and atopic dermatitis patients. Skin homeostasis parameters between healthy skin, uninvolved AD skin and AD eczematous lesions were compared (Figure 2, Table S1). TEWL was lower on healthy skin than uninvolved AD skin (9.98 vs. 25.51 g · m −2· h −1 ,p< 0.001) and AD eczematous lesions (9.98 vs. 28.38 g · m −2· h −1 ,p< 0.001), while no differences between uninvolved AD skin and AD eczematous lesion were found. SCH was lower on AD eczematous lesions than uninvolved AD skin (24.23 vs. 39.36 AU, p< 0.001) and healthy skin (24.23 vs. 44.36 AU, p< 0.001). Temperature was higher on AD eczematous lesions compared with uninvolved AD skin (32.07 vs. 31.28 ◦ C, p< 0.001) and healthy skin (32.07 vs. 31.11 ◦ C, p< 0.001). Erythema was higher on AD eczematous lesion than uninvolved AD skin (391.11 vs. 239.88 AU, p< 0.001) and healthy skin (391.11 vs. 218.93 AU, p< 0.001). pH was higher on AD eczematous lesions compared with healthy skin (6.15 vs. 5.92, p= 0.039). Elasticity was lower on AD eczematous lesions than uninvolved AD skin (0.69 vs. 0.74, p= 0.038) and healthy skin (0.69 vs. 0.77, p= 0.014). Life 2022,12, 132 5 of 14 Life 2022, 12, x FOR PEER REVIEW 5 of 14 Figure 2. Skin barrier function parameters between patients with atopic dermatitis and healthy volunteers. AD, atopic dermatitis; AU, arbitrary units; SCH, stratum corneum hydration; TEWL, transepidermal water loss Ninety-three participants were <30 years and 69 were ≥30 years of age. Sex, smoking/drinking habits, and emollients use was similar between the two age groups. Disease severity was compared between AD patients <30 and ≥30 years, Figure 3. AD patients ≥30 years had a tendentially higher EASI than AD patients <30 years (21.96 vs. 17.68, p = 0.090) while there were no differences regarding SCORAD (45.57 vs. 38.39 respectively, p = 0.166). Figure 3. Disease severity depending on the age. p-value after using Student’s t-test for independent samples to compare disease severity between patients with atopic dermatitis < 30 and ≥ 30 years of age. Figure 2. Skin barrier function parameters between patients with atopic dermatitis and healthy volunteers. AD, atopic dermatitis; AU, arbitrary units; SCH, stratum corneum hydration; TEWL, transepidermal water loss. Ninety-three participants were <30 years and 69 were ≥ 30 years of age. Sex, smoking/drinking habits, and emollients use was similar between the two age groups. Disease severity was compared between AD patients <30 and ≥ 30 years, Figure 3. AD patients ≥ 30 years had a tendentially higher EASI than AD patients <30 years (21.96 vs. 17.68, p= 0.090) while there were no differences regarding SCORAD (45.57 vs. 38.39 respectively, p= 0.166). Life 2022, 12, x FOR PEER REVIEW 5 of 14 Figure 2. Skin barrier function parameters between patients with atopic dermatitis and healthy volunteers. AD, atopic dermatitis; AU, arbitrary units; SCH, stratum corneum hydration; TEWL, transepidermal water loss Ninety-three participants were <30 years and 69 were ≥30 years of age. Sex, smoking/drinking habits, and emollients use was similar between the two age groups. Disease severity was compared between AD patients <30 and ≥30 years, Figure 3. AD patients ≥30 years had a tendentially higher EASI than AD patients <30 years (21.96 vs. 17.68, p = 0.090) while there were no differences regarding SCORAD (45.57 vs. 38.39 respectively, p = 0.166). Figure 3. Disease severity depending on the age. p-value after using Student’s t-test for independent samples to compare disease severity between patients with atopic dermatitis < 30 and ≥ 30 years of age. Figure 3. Disease severity depending on the age. p-value after using Student’s t-test for independent samples to compare disease severity between patients with atopic dermatitis < 30 and ≥ 30 years of age. Life 2022,12, 132 6 of 14 Regarding participants <30 years of age (Table S2), TEWL was lower on healthy skin than uninvolved AD skin (9.99 vs. 25.69 g · m −2· h −1 ,p< 0.001) and AD eczematous lesions (9.99 vs. 28.32 g · m −2· h −1 ,p< 0.001) but it did not differ between AD eczematous lesions and uninvolved AD skin (Figure 4A). SCH was lower on AD eczematous lesions than uninvolved AD skin (22.47 vs. 38.22 AU, p< 0.001) and healthy individuals (22.47 vs. 48.13 AU, p< 0.001) and it was also lower on uninvolved AD skin than healthy individuals (38.22 vs. 48.13 AU, p= 0.030) (Figure 5A). Temperature was higher on AD eczematous lesions than uninvolved AD skin (31.94 vs. 31.05, p< 0.001) and healthy skin (31.94 vs. 31.07 ◦ C, p= 0.010) but it did not differ between uninvolved AD skin and healthy skin (Figure 6A). Erythema was higher on AD eczematous lesions than uninvolved AD skin (388.80 vs. 226.75 AU, p< 0.001) and healthy skin (388.80 vs. 226.73 AU, p< 0.001), but it did not differ between uninvolved AD skin and healthy skin (Figure 7A). pH was lower on healthy volunteers than uninvolved AD skin (5.81 vs. 6.16, p= 0.029) and AD eczematous lesions (5.81 vs. 6.23, p= 0.008) but it did not differ between uninvolved AD skin and AD eczematous lesions (Figure 8A). Elasticity was lower on AD eczematous lesions than uninvolved AD skin (0.71 vs. 0.78, p= 0.003) and on healthy skin (0.71 vs. 0.79, p= 0.040) but it did not differ between uninvolved AD skin and healthy skin (Figure 9A). Life 2022, 12, x FOR PEER REVIEW 6 of 14 Regarding participants <30 years of age (Table S2), TEWL was lower on healthy skin than uninvolved AD skin (9.99 vs. 25.69 g·m−2·h−1, p < 0.001) and AD eczematous lesions (9.99 vs. 28.32 g·m−2·h−1, p < 0.001) but it did not differ between AD eczematous lesions and uninvolved AD skin (Figure 4A). SCH was lower on AD eczematous lesions than uninvolved AD skin (22.47 vs. 38.22 AU, p < 0.001) and healthy individuals (22.47 vs. 48.13 AU, p < 0.001) and it was also lower on uninvolved AD skin than healthy individuals (38.22 vs. 48.13 AU, p = 0.030) (Figure 5A). Temperature was higher on AD eczematous lesions than uninvolved AD skin (31.94 vs. 31.05, p < 0.001) and healthy skin (31.94 vs. 31.07 °C, p = 0.010) but it did not differ between uninvolved AD skin and healthy skin (Figure 6A). Erythema was higher on AD eczematous lesions than uninvolved AD skin (388.80 vs. 226.75 AU, p < 0.001) and healthy skin (388.80 vs. 226.73 AU, p < 0.001), but it did not differ between uninvolved AD skin and healthy skin (Figure 7A). pH was lower on healthy volunteers than uninvolved AD skin (5.81 vs. 6.16, p = 0.029) and AD eczematous lesions (5.81 vs. 6.23, p = 0.008) but it did not differ between uninvolved AD skin and AD eczematous lesions (Figure 8A). Elasticity was lower on AD eczematous lesions than uninvolved AD skin (0.71 vs. 0.78, p = 0.003) and on healthy skin (0.71 vs. 0.79, p = 0.040) but it did not differ between uninvolved AD skin and healthy skin (Figure 9A). Figure 4. Transepidermal water loss comparing (A) patients with atopic dermatitis < 30 and healthy participants < 30, and (B) patients with atopic dermatitis ≥ 30 and healthy participants ≥ 30. Concerning adults ≥ 30 years of age (Table S3), TEWL was lower on healthy skin than uninvolved AD skin (10.75 vs. 25.18 g·m−2·h−1, p = 0.001) and AD eczematous lesions (10.75 vs. 28.48 g·m−2·h−1, p < 0.001) but it did not differ between uninvolved AD skin and AD eczematous lesions (Figure 4B). SCH was lower on AD eczematous lesions than on uninvolved AD skin (27.63 vs. 41.56 AU, p = 0.001) and healthy skin (27.63 vs. 43.16 AU, p < 0.001) but it did not differ between uninvolved AD skin and healthy skin (Figure 5B). Temperature was higher on AD eczematous lesions than uninvolved AD skin (32.30 vs. 31.70 °C, p = 0.011) and healthy skin (32.30 vs. 31.17 °C, p < 0.001) and it was also higher on uninvolved AD skin than healthy skin (31.70 vs. 31.17°C, p = 0.042) (Figure 6B). Erythema was higher on AD eczematous lesions than uninvolved AD skin (395.32 vs. 263.82 AU, p < 0.001) and healthy skin (395.32 vs. 214.08 AU, p < 0.001) and it was also higher on Figure 4. Transepidermal water loss comparing ( A ) patients with atopic dermatitis < 30 and healthy participants < 30, and (B) patients with atopic dermatitis ≥30 and healthy participants ≥30. Concerning adults ≥ 30 years of age (Table S3), TEWL was lower on healthy skin than uninvolved AD skin (10.75 vs. 25.18 g · m −2· h −1 ,p= 0.001) and AD eczematous lesions (10.75 vs. 28.48 g · m −2· h −1 ,p< 0.001) but it did not differ between uninvolved AD skin and AD eczematous lesions (Figure 4B). SCH was lower on AD eczematous lesions than on uninvolved AD skin (27.63 vs. 41.56 AU, p= 0.001) and healthy skin (27.63 vs. 43.16 AU, p< 0.001) but it did not differ between uninvolved AD skin and healthy skin (Figure 5B). Temperature was higher on AD eczematous lesions than uninvolved AD skin (32.30 vs. 31.70 ◦ C, p= 0.011) and healthy skin (32.30 vs. 31.17 ◦ C, p< 0.001) and it was also higher on uninvolved AD skin than healthy skin (31.70 vs. 31.17 ◦ C, p= 0.042) (Figure 6B). Erythema was higher on AD eczematous lesions than uninvolved AD skin (395.32 vs. 263.82 AU, p< 0.001) and healthy skin (395.32 vs. 214.08 AU, p< 0.001) and it was also higher on uninvolved AD skin than healthy skin (263.82 vs. 214.08 AU, p= 0.004) (Figure 7B). Elasticity was higher on healthy skin than uninvolved AD skin (0.74 vs. 0.65, p Life 2022,12, 132 7 of 14 = 0.043) and AD eczematous lesions (0.74 vs. 0.65, p= 0.040) but it did not differ between AD eczematous lesions and uninvolved AD skin (Figure 9B). pH did not differ between AD eczematous lesions, uninvolved AD skin and healthy skin (Figure 8B). Life 2022, 12, x FOR PEER REVIEW 7 of 14 uninvolved AD skin than healthy skin (263.82 vs. 214.08 AU, p = 0.004) (Figure 7B). Elasticity was higher on healthy skin than uninvolved AD skin (0.74 vs. 0.65, p = 0.043) and AD eczematous lesions (0.74 vs. 0.65, p = 0.040) but it did not differ between AD eczematous lesions and uninvolved AD skin (Figure 9B). pH did not differ between AD eczematous lesions, uninvolved AD skin and healthy skin (Figure 8B). Figure 5. Stratum corneum hydration comparing (A) patients with atopic dermatitis < 30 and healthy participants < 30, and (B) patients with atopic dermatitis ≥ 30 and healthy participants ≥ 30. Figure 6. Temperature comparing (A) patients with atopic dermatitis < 30 and healthy participants < 30, and (B) patients with atopic dermatitis ≥ 30 and healthy participants ≥ 30. Figure 5. Stratum corneum hydration comparing ( A ) patients with atopic dermatitis < 30 and healthy participants < 30, and (B) patients with atopic dermatitis ≥30 and healthy participants ≥30. Life 2022, 12, x FOR PEER REVIEW 7 of 14 uninvolved AD skin than healthy skin (263.82 vs. 214.08 AU, p = 0.004) (Figure 7B). Elasticity was higher on healthy skin than uninvolved AD skin (0.74 vs. 0.65, p = 0.043) and AD eczematous lesions (0.74 vs. 0.65, p = 0.040) but it did not differ between AD eczematous lesions and uninvolved AD skin (Figure 9B). pH did not differ between AD eczematous lesions, uninvolved AD skin and healthy skin (Figure 8B). Figure 5. Stratum corneum hydration comparing (A) patients with atopic dermatitis < 30 and healthy participants < 30, and (B) patients with atopic dermatitis ≥ 30 and healthy participants ≥ 30. Figure 6. Temperature comparing (A) patients with atopic dermatitis < 30 and healthy participants < 30, and (B) patients with atopic dermatitis ≥ 30 and healthy participants ≥ 30. Figure 6. Temperature comparing ( A ) patients with atopic dermatitis < 30 and healthy participants < 30, and (B) patients with atopic dermatitis ≥30 and healthy participants ≥30. Life 2022,12, 132 8 of 14 Life 2022, 12, x FOR PEER REVIEW 8 of 14 Figure 7. Erythema comparing (A) patients with atopic dermatitis < 30 and healthy participants < 30, and (B) patients with atopic dermatitis ≥ 30 and healthy participants ≥ 30. Figure 8. pH comparing (A) patients with atopic dermatitis < 30 and healthy participants < 30, and (B) patients with atopic dermatitis ≥ 30 and healthy participants ≥ 30. Figure 7. Erythema comparing ( A ) patients with atopic dermatitis < 30 and healthy participants < 30, and (B) patients with atopic dermatitis ≥30 and healthy participants ≥30. Life 2022, 12, x FOR PEER REVIEW 8 of 14 Figure 7. Erythema comparing (A) patients with atopic dermatitis < 30 and healthy participants < 30, and (B) patients with atopic dermatitis ≥ 30 and healthy participants ≥ 30. Figure 8. pH comparing (A) patients with atopic dermatitis < 30 and healthy participants < 30, and (B) patients with atopic dermatitis ≥ 30 and healthy participants ≥ 30. Figure 8. pH comparing ( A ) patients with atopic dermatitis < 30 and healthy participants < 30, and (B) patients with atopic dermatitis ≥30 and healthy participants ≥30. Life 2022,12, 132 9 of 14 Life 2022, 12, x FOR PEER REVIEW 9 of 14 Figure 9. Elasticity comparing (A) patients with atopic dermatitis < 30 and healthy participants < 30, and (B) patients with atopic dermatitis ≥ 30 and healthy participants ≥ 30. A negative correlation was found between age and elasticity in all the population (r = −0.383, p < 0.001). This correlation was stronger in AD patients (r = −0.494, p < 0.001) than in controls (r = −0.266, p = 0.092), Figure 10. Moreover, on uninvolved AD skin (Figure S1), SCORAD was positively correlated to pH (r = 0.401, p = 0.001) and negatively correlated to SCORAD and TEWL (r = −0.672, p < 0.001), SCH (r = −0.504, p < 0.001) and elasticity (r = −0.541, p < 0.001). A correlation close to significance was found between SCORAD and erythema on uninvolved skin (r = 0.250, p = 0.090). No significative correlations were found between SCORAD and temperature (r = 0.002, p = 0.968). On AD eczematous lesions (Figure S2), a positive correlation was found between SCORAD and temperature (r = 0.291, p = 0.011) and between SCORAD and pH (r = 0.401, p < 0.001); and a negative correlation between SCORAD and SCH (r = −0.319, p = 0.006) and between SCORAD and elasticity (r = −0.419, p = 0.003). A correlation close to significance was found between SCORAD and erythema on eczematous lesions (r = 0.258, p = 0.080). No correlation was found between SCORAD and TEWL (r = −0.016, p = 0.892). After conducting a linear regression model in AD patients adjusted by age, sex and SCORAD, it was found that elasticity was impaired by a higher age (β = −0.004, p < 0.001) and a higher SCORAD (β = −0.003, p < 0.001). Figure 9. Elasticity comparing ( A ) patients with atopic dermatitis < 30 and healthy participants < 30, and (B) patients with atopic dermatitis ≥30 and healthy participants ≥30. A negative correlation was found between age and elasticity in all the population (r = − 0.383, p< 0.001). This correlation was stronger in AD patients (r = − 0.494, p< 0.001) than in controls (r = − 0.266, p= 0.092), Figure 10. Moreover, on uninvolved AD skin (Figure S1), SCORAD was positively correlated to pH (r = 0.401, p= 0.001) and negatively correlated to SCORAD and TEWL (r = − 0.672, p< 0.001), SCH (r = − 0.504, p< 0.001) and elasticity (r = − 0.541, p< 0.001). A correlation close to significance was found between SCORAD and erythema on uninvolved skin (r = 0.250, p= 0.090). No significative correlations were found between SCORAD and temperature (r = 0.002, p= 0.968). On AD eczematous lesions (Figure S2), a positive correlation was found between SCORAD and temperature (r = 0.291, p= 0.011) and between SCORAD and pH (r = 0.401, p< 0.001); and a negative correlation between SCORAD and SCH (r = − 0.319, p= 0.006) and between SCORAD and elasticity (r = − 0.419, p= 0.003). A correlation close to significance was found between SCORAD and erythema on eczematous lesions (r = 0.258, p= 0.080). No correlation was found between SCORAD and TEWL (r = − 0.016, p= 0.892). After conducting a linear regression model in AD patients adjusted by age, sex and SCORAD, it was found that elasticity was impaired by a higher age (β=−0.004, p< 0.001) and a higher SCORAD (β=−0.003, p< 0.001).