From consistent subjective assessment of skin sensitivity severity to its accurate objective scoring.

BACKGROUND: Sensitive skin (SenS) is a syndrome leading to unpleasant sensations with little visible signs. Grading its severity generally relies on questionnaires or subjective ratings. MATERIALS AND METHODS: The SenS status of 183 subjects was determined by trained assessors. Answers from a four-item questionnaire were converted into numerical scores, leading to a 0-15 SenS index that was asked twice or thrice. Parameters from hyperspectral images were used as input for a multi-layer perceptron (MLP) neural network to predict the four-item questionnaire score of subjects. The resulting model was used to evaluate the soothing effect of a cosmetic cream applied to one hemiface, comparing it to that of a placebo applied to the other hemiface. RESULTS: The four-item questionnaire score accurately predicts SenS assessors' classification (92.7%) while providing insight into SenS severity. Most subjects providing repeatable replies are non-SenS, but accepting some variability in answers enables identifying subjects with consistent replies encompassing a majority of SenS subjects. The MLP neural network model predicts the SenS score of subjects with consistent replies from full-face hyperspectral images (R2 Validation set  = 0.969). A similar quality is obtained with hemiface images. Comparing the effect of applying a soothing cosmetic to that of a placebo revealed that subjects with the highest instrumental index (> 5) show significant SenS improvement. CONCLUSION: A four-item questionnaire enables calculating a SenS index grading its severity. Objective evaluation using hyperspectral images with an MLP neural network accurately predicts SenS severity and its favourable evolution upon the application of a soothing cream.

Skin homeostasis: Mechanism and influencing factors.

BACKGROUND: The skin is the largest organ in the human body, not only resisting the invasion of harmful substances, but also preventing the loss of moisture and nutrients. Maintaining skin homeostasis is a prerequisite for the proper functioning of the body. Any damage to the skin can lead to a decrease in local homeostasis, such as ultraviolet radiation, seasonal changes, and air pollution, which can damage the skin tissue and affect the function of the skin barrier. OBJECTIVE: This article reviews the maintenance mechanism and influencing factors of skin homeostasis and the symptoms of homeostasis imbalance. METHODS: We searched for articles published between 1990 and 2022 in English and Chinese using PubMed, Web of Science, CNKI, and other databases in the subject area of dermatology, using the following search terms in various combinations: "skin homeostasis," "skin barrier," and "unstable skin." Based on our results, we further refined our search criteria to include a series of common skin problems caused by the destruction of skin homeostasis and its treatments. Limitations include the lack of research on dermatological and cosmetic problems triggered by the disruption of skin homeostasis. RESULTS: This study describes the neuroendocrine-immune system, skin barrier structure, and skin metabolic system that maintain skin homeostasis. In addition, we discuss several common symptoms that occur when skin homeostasis is out of balance, such as dryness, redness, acne, sensitivity, and aging, and explain the mechanism of these symptoms. CONCLUSION: This article provides an update and review for students and practitioners, and provides a theoretical basis for the development of skin care products for the maintenance and repair of skin homeostasis.

Investigating the impact of sebum secretion on liquid makeup foundation darkening and its solution.

OBJECTIVES: Darkening has been an issue of concern for foundation products. The secretion of sebum plays a significant role in the process of foundation darkening, but the underlying mechanisms and solutions have been rarely reported. The aim of this study was to explore the relationship between sebum secretion and liquid foundation darkening and to provide possible solutions for reducing sebum-induced darkening in liquid foundation. METHODS: Artificial sebum in different concentrations was added to a basic liquid foundation to simulate different stages of sebum secretion. The colour of the mixture was then measured by a spectrophotometer on the standard opacity chart. Potential technical solutions for anti-darkening were applied to a basic liquid foundation, and its ability to anti-darkening was further verified in vivo. RESULTS: (1) The influences of sebum addition on liquid foundation darkening had a significant positive correlation with the increase in transmissivities (R2 = 0.852, p < 0.01). (2) A certain range of sebum addition can reduce the darkening of volatile foundations. (3) The liquid foundations using pigments with high dispersibility in sebum were less influenced by sebum. (4) The replacement of pigments with oil-fixing ability could effectively reduce the darkening of liquid foundations induced by sebum (p < 0.01). CONCLUSION: The effect of sebum on the darkening of liquid foundation was accompanied by a greater transmissivity as its pigment concentration decreased. Balanced volatility, the addition of powders with higher sebum dispersibility and the replacement of oil-fixing powders could reduce the darkening of the liquid foundation caused by sebum secretion.

OBJECTIFS: L'assombrissement a été un problème de préoccupation pour les produits de fond de teint. La sécrétion de sébum joue un rôle significatif dans le processus d'assombrissement du fond de teint, mais les mécanismes sous-jacents et les solutions ont été rarement rapportés. L'objectif de cette étude était d'explorer la relation entre la sécrétion de sébum et l'assombrissement du fond de teint liquide, et de fournir des solutions possibles pour réduire l'assombrissement induit par le sébum dans le fond de teint liquide. MÉTHODES: Du sébum artificiel à différentes concentrations a été ajouté à un fond de teint liquide de base pour simuler différents stades de sécrétion de sébum. La couleur du mélange a ensuite été mesurée par un spectrophotomètre sur le tableau standard d'opacité. Des solutions techniques potentielles pour l'anti-assombrissement ont été appliquées à un fond de teint liquide de base et leur capacité à prévenir l'assombrissement a été vérifiée in vivo. RÉSULTATS: (1) Les influences de l'ajout de sébum sur l'assombrissement du fond de teint liquide avaient une corrélation significativement positive avec l'augmentation des transmissivités (R2 = 0.852 p < 0.01). (2) Une certaine plage de concentration de sebum peut réduire l'assombrissement des fondations volatiles. (3) Les fonds de teint liquides utilisant des pigments à haute dispersibilité dans le sébum étaient moins influencés par le sébum. (4) Le remplacement des pigments par des poudres à capacité de fixation d'huile pouvait efficacement réduire l'assombrissement des fonds de teint liquides induit par le sébum (p < 0.01). CONCLUSION: L'effet du sébum sur l'assombrissement du fond de teint liquide était accompagné d'une plus grande transmissivité à mesure que la concentration de son pigment diminuait. La volatilité équilibrée, l'ajout de poudres à plus grande dispersibilité de sébum et le remplacement de poudres à capacité de fixation d'huile pourraient réduire l'assombrissement du fond de teint liquide causé par la sécrétion de sébum.

Revitalizing the skin: Exploring the role of barrier repair moisturizers.

BACKGROUND: Moisturizers are designed to maintain skin health and treat dermatological conditions associated with impaired skin barrier function. However, differences in their composition account for the differences in their effect. AIMS: This narrative review aims to discuss the role of barrier repair moisturizers, highlight the role of different components in a moisturizer and their role in impaired skin conditions (e.g., dry, itchy, inflamed, sensitive skin, atopic eczema), and thereby empower dermatologists and pediatricians in selecting the right moisturizer. METHODS: PubMed, Embase, and Scopus electronic databases were searched from January 2000 to June 2023 for publications on skin barrier repair and use of barrier repair moisturizers for the treatment of dry, itchy, inflamed, sensitive skin, or atopic eczema. Studies conducted in humans, published in English for which full texts were freely available were included. RESULTS: The structure and composition of lipid lamellae within the stratum corneum play an important role in maintaining an effective skin barrier and protecting the body from various external assaults. Endocannabinoid mediators play an active role in maintaining skin barrier function. Moisturizers containing physiological lipids and functional ingredients (e.g., endocannabinoids such as palmitoylethanolamide [PEA]) and based on the principles of biomimic technology are demonstrated to be beneficial for the management of conditions associated with a disrupted skin barrier. CONCLUSIONS: Moisturizer based on the innovative biomimic formulation has good cosmetic efficacy and is generally well tolerated, and the addition of PEA might represent a new generation of compounds that may be beneficial for long-term management of impaired skin conditions.

How Skin Color Depends on Tissue Oxygenation.

BACKGROUND: Skin color is essential to skin and wound assessment as it brings valuable information about skin physiology and pathology. An approach, which can help deconvolute and isolate various mechanisms affecting skin color, could be helpful to drive the remote photoplethysmography (rPPG) utility beyond its current applications. AIM: The present work aims to create a simple analytical framework that links skin color with blood oxygenation and perfusion. MATERIAL AND METHODS: The model consists of two parts. First, the model's core connects changes in tissue chromophore concentrations with changes in tissue reflectance. In the second step, the tissue reflectance is convoluted with the response curves of a sensor (tristimulus response in the case of the human eye) and the light source's spectrum. RESULTS: The model allows linking changes in blood oxygenation and perfusion with changes in skin color. CONCLUSION: The model can be helpful for the interpretation of the amplitudes of various components of the rPPG signal.

The Five Basic Human Senses Evoke Electrodermal Activity.

Electrodermal activity (EDA) usually relates to variations in the electrical properties of palmar or plantar skin sites. EDA responses, namely skin conductance responses (SCRs), skin potential responses (SPRs) and skin susceptance responses (SSRs) are shown to be sensitive indexes of sympathetic nervous system activation and are studied in many research projects. However, the association between EDA responses and the five basic human senses has not been investigated yet. Our study aimed to explore the relationship between the three EDA responses (SCRs, SSRs and SPRs) and the five basic human senses. These three EDA responses were measured simultaneously at the same skin site on each of the 38 volunteers. The tested five senses were sight, hearing, touch, taste and smell. The results showed that the different tested senses led to different degrees of EDA responses due to activation of the sympathetic nervous system and corresponding secretion of sweat. Although a controlled study on the degree of EDA as a function of the strength of each stimulus was not performed, we noted that the largest EDA responses were typically associated with the smell sense test. We conclude that EDA responses could be utilized as measures for examining the sensitivity of the human senses. Hence, EDA devices may have important roles in sensory systems for future clinical applications.

Molecular insights of human skin epidermal and dermal aging.

Human skin is the most widespread and abundant type of tissue in the human body. With the passage of time, most of our organs, including a substantial part of the skin, tend to undergo a gradual thinning or decrease in size. As we age, there is a gradual and progressive reduction in the thickness of both the epidermis and dermis layers of our skin. This is primarily attributed to the decline of epidermal stem cells and the loss of dermal collagen, which is the most abundant protein in the human body. Age-related alterations of the epidermis and dermis impair skin structure/function and create a tissue microenvironment that promotes age-related skin diseases, such as impaired skin barrier, delayed wound healing, and skin cancer development. This review will examine the current body of literature pertaining to our knowledge of skin epidermal and dermal aging.

Emergence of New Concepts in Skin Physiopathology through the Use of in vitro Human Skin Explants Models.

BACKGROUND: This review summarizes uses and new applications for dermatological research of in vitro culture models of human skin explants (HSEs). In the last decade, many innovations have appeared in the literature and an exponential number of studies have been recorded in various fields of application such as process culture engineering, stem cell extractions methodology, or cell-to-cell interaction studies under physiological and pathological conditions, wound-healing, and inflammation. Most studies also concerned pharmacology, cosmetology, and photobiology. However, these topics will not be considered in our review. SUMMARY: A better understanding of the mechanisms driving intercellular relationships, at work in the maintenance of 3D tissue architectures has led to the improvement of cell culture techniques. Many papers have focused on the physiological ways that govern in vitro tissue maintenance of HSEs. The analysis of the necessary mechanical stress, intercellular and cell-matrix interactions, allows the maintenance and prolonged use of HSEs in culture for up to 15 days, regardless of the great variability of study protocols from one laboratory to another and in accordance with the objectives set. Because of their close similarities to fresh skin, HSEs are increasingly used to study skin barrier repair and wound healing physiology. Easy to use in co-culture, this model allows a better understanding of the connections and interactions between the peripheral nervous system, the skin and the immune system. The development of the concept of an integrated neuro-immuno-cutaneous system at work in skin physiology and pathology highlighted by this article represents one of the new technical challenges in the field of in vitro culture of HSE. This review of the literature also reveals the importance of using such models in pathology. As sources of stem cells, HSEs are the basis for the development of new tissue engineering models such as organoids or optical clearing tissues technology. This study identifies the main advances and cross-cutting issues in the use of HSE.

Bio-potential noise of dry printed electrodes: physiology versus the skin-electrode impedance.

Objective. To explore noise characteristics and the effect physiological activity has on the link between impedance and noise.Approach. Dry-printed electrodes are emerging as a new and exciting technology for skin electro-physiology. Such electrode arrays offer many advantages including user convenience, quick placement, and high resolution. Here we analyze extensive electro-physiological data recorded from the arm and the face to study and quantify the noise of dry electrodes, and to characterize the link between noise and impedance. In particular, we studied the effect of the physiological state of the subject (e.g. rapid eye movement sleep) on noise.Main results. We show that baseline noise values extracted from dry electrodes in the arm are in agreement with the Nyquist equation. In the face, on the other hand, the measured noise values were higher than the values predicted by the Nyquist equation. In addition, we studied how different electrode properties affect performances, including electrode size, shape, and material properties.Significance. Altogether, the results presented here provide a basis for understanding dry electrode performances and substantiate their great potential in electro-physiological investigations.

Intradermal Microdialysis: An Approach to Investigating Novel Mechanisms of Microvascular Dysfunction in Humans.

The cutaneous vasculature is an accessible tissue that can be used to assess microvascular function in humans. Intradermal microdialysis is a minimally invasive technique used to investigate mechanisms of vascular smooth muscle and endothelial function in the cutaneous circulation. This technique allows for the pharmacological dissection of the pathophysiology of microvascular endothelial dysfunction as indexed by decreased nitric oxide-mediated vasodilation, an indicator of cardiovascular disease development risk. In this technique, a microdialysis probe is placed in the dermal layer of the skin, and a local heating unit with a laser Doppler flowmetry probe is placed over the probe to measure the red blood cell flux. The local skin temperature is clamped or stimulated with direct heat application, and pharmacological agents are perfused through the probe to stimulate or inhibit intracellular signaling pathways in order to induce vasodilation or vasoconstriction or to interrogate mechanisms of interest (co-factors, antioxidants, etc.). The cutaneous vascular conductance is quantified, and mechanisms of endothelial dysfunction in disease states can be delineated.

Investigating causal relationships between obesity and skin barrier function in a multi-ethnic Asian general population cohort.

BACKGROUND: Skin diseases impact significantly on the quality of life and psychology of patients. Obesity has been observed as a risk factor for skin diseases. Skin epidermal barrier dysfunctions are typical manifestations across several dermatological disturbances. OBJECTIVES: We aim to establish the association between obesity and skin physiology measurements and investigate whether obesity may play a possible causal role on skin barrier dysfunction. METHODS: We investigated the relationship of obesity with skin physiology measurements, namely transepidermal water loss (TEWL), skin surface moisture and skin pH in an Asian population cohort (n = 9990). To assess for a possible causal association between body mass index (BMI) and skin physiology measurements, we performed Mendelian Randomization (MR), along with subsequent additional analyses to assess the potential causal impact of known socioeconomic and comorbidities of obesity on TEWL. RESULTS: Every 1 kg/m2 increase in BMI was associated with a 0.221% (95%CI: 0.144-0.298) increase in TEWL (P = 2.82E-08), a 0.336% (95%CI: 0.148-0.524) decrease in skin moisture (P = 4.66E-04) and a 0.184% (95%CI: 0.144-0.224) decrease in pH (P = 1.36E-19), adjusting for age, gender, and ethnicity. Relationships for both TEWL and pH with BMI remained strong (Beta 0.354; 95%CI: 0.189-0.520 and Beta -0.170; 95%CI: -0.253 to -0.087, respectively) even after adjusting for known confounders, with MR experiments further supporting BMI's possible causal relationship with TEWL. Based on additional MR performed, none of the socioeconomic and comorbidities of obesity investigated are likely to have possible causal relationships with TEWL. CONCLUSION: We establish strong association of BMI with TEWL and skin pH, with MR results suggestive of a possible causal relationship of obesity with TEWL. It emphasizes the potential impact of obesity on skin barrier function and therefore opportunity for primary prevention.

Evaluation of the effects of 10% and 30% gluconolactone chemical peel on sebum, pH, and TEWL.

BACKGROUND: Gluconolactone (GLA) exhibits antioxidant and moisturizing effects. It also presents soothing effects, protects elastin fibers from UV-induced degradation, and improves the function of the skin barrier. AIMS: Evaluation of skin parameters such as pH, transepidermal water loss (TEWL), sebum levels before, during, and after a series of applications of 10% and 30% GLA chemical peel in a split-face model. MATERIALS AND METHODS: The study involved 16 female subjects. Three split-face procedures were performed using two concentrations of GLA solution applied on two sides of the face. The skin parameters were measured before treatments and 7 days after the last procedure at four measurement sites on either side of the face, that is, on the forehead, around the eye, on the cheek, and on the nose wing. RESULTS: Measurement of sebum demonstrated some statistically significant changes between sebum levels in the cheeks after a series of treatments. The pH measurement showed that the pH value was reduced after each treatment at all measurement points. The level of TEWL after treatments was significantly lower around the eyes, on the left forehead, and on the right cheek. There were no significant differences between the use of different concentrations of the GLA solution. CONCLUSIONS: The results of the study show that GLA has a significant influence on lowering skin pH and TEWL. GLA also has seboregulatory properties.

Does thermal biology differ between two colour pattern morphs of a widespread Australian lizard?

Alternative phenotypes allow individuals to pursue different adaptive pathways in response to the same selective challenge. Colour polymorphic species with geographically varying morph frequencies may reflect multiple adaptations to spatial variables such as temperature and climate. We examined whether thermal biology differed between colour morphs of an Australian lizard, the delicate skink, Lampropholis delicata. The delicate skink has two colour pattern morphs, with frequencies varying across latitude and sex: plain (darker, more common at temperate latitudes, more common in males) or striped (lighter, more common at lower latitudes, more common in females). We tested heating and cooling rate, sprint speed, thermal preference, field body temperature and metabolic rate in both morphs and sexes to determine any link between colour and morph frequency distribution. Plain individuals heated more quickly, but other thermal traits showed little variation among morphs. Lampropholis delicata colour influences rates of heat exchange, but the relationship does not appear to be adaptive, suggesting that behavioural thermoregulation homogenises body temperature in the field. While we find no substantial evidence of thermal differences between the two colour morphs, morph-specific behaviour may buffer against differences in heat exchange. Latitudinal variation in species colour may be driven by selection pressures other than temperature.

Skin maturation from birth to 10 years of age: Structure, function, composition and microbiome.

Infant and adult skin physiology differ in many ways; however, limited data exist for older children. To further investigate the maturation processes of healthy skin during childhood. Skin parameters were recorded in 80 participants of four age groups: babies (0-2 years), young children (3-6 years), older children (7-<10 years) and adults (25-40 years). Overall, skin barrier function continues to mature, reaching adult levels of transepidermal water loss (TEWL), lipid compactness, stratum corneum (SC) thickness and corneocyte size by the age of about 6 years. Higher levels of lactic acid and lower levels of total amino acids in the SC of babies and young children further indicate higher cell turnover rates. In all age groups, TEWL and skin surface hydration values remain higher on the face compared with the arm. Skin becomes darker and contains higher levels of melanin with increasing age. The composition of skin microbiome of the dorsal forearm in all children groups is distinct from that in adults, with Firmicutes predominating in the former and Proteobacteria in the latter. Skin physiology, along with the skin microbiome, continues to mature during early childhood in a site-specific manner.

The role of the dorsolateral prefrontal cortex in control of skin sympathetic nerve activity in humans.

The dorsolateral prefrontal cortex (dlPFC) is primarily involved in higher order executive functions, with there being evidence of lateralization. Brain imaging studies have revealed its link to the generation of skin sympathetic nerve activity (SSNA), which is elevated in states of emotional arousal or anxiety. However, no studies have directly explored dlPFC influences on SSNA. Transcranial alternating current stimulation (-2 to 2 mA, 0.08 Hz, 100 cycles) was applied between the left or right dlPFC and nasion via surface electrodes. Spontaneous bursts of SSNA were recorded from the common peroneal nerve via a tungsten microelectrode in 21 healthy participants. The modulation index was calculated for each stimulation paradigm by constructing cross-correlation histograms between SSNA and the sinusoidal stimulus. Stimulation of the dlPFC caused significant modulation of SSNA, but there was no significant difference in the median modulation index across sides. Stimulation also caused cyclic modulation of skin blood flow and sweat release. We have shown for the first time that stimulation of the dlPFC causes modulation of SSNA, also reflected in the effector-organ responses. This supports a role for the dlPFC in the control of SSNA, which likely contributes to the ability of emotions to bring about cutaneous vasoconstriction and sweat release.

Recent Advances in Multiplexed Wearable Sensor Platforms for Real-Time Monitoring Lifetime Stress: A Review.

Researchers are interested in measuring mental stress because it is linked to a variety of diseases. Real-time stress monitoring via wearable sensor systems can aid in the prevention of stress-related diseases by allowing stressors to be controlled immediately. Physical tests, such as heart rate or skin conductance, have recently been used to assess stress; however, these methods are easily influenced by daily life activities. As a result, for more accurate stress monitoring, validations requiring two or more stress-related biomarkers are demanded. In this review, the combinations of various types of sensors (hereafter referred to as multiplexed sensor systems) that can be applied to monitor stress are discussed, referring to physical and chemical biomarkers. Multiplexed sensor systems are classified as multiplexed physical sensors, multiplexed physical-chemical sensors, and multiplexed chemical sensors, with the effect of measuring multiple biomarkers and the ability to measure stress being the most important. The working principles of multiplexed sensor systems are subdivided, with advantages in measuring multiple biomarkers. Furthermore, stress-related chemical biomarkers are still limited to cortisol; however, we believe that by developing multiplexed sensor systems, it will be possible to explore new stress-related chemical biomarkers by confirming their correlations to cortisol. As a result, the potential for further development of multiplexed sensor systems, such as the development of wearable electronics for mental health management, is highlighted in this review.

Effects of Early Emollient Use in Children at High Risk of Atopic Dermatitis: A German Pilot Study.

Several small studies have indicated that daily emollient use from birth might delay, suppress or prevent atopic dermatitis (AD). Two larger trials did not confirm this; however, a recent smaller study indicated a protective effect if daily emollient use is used in the first 2 months of life. Further research is needed to evaluate the effect of emollient use on development of AD. The current study randomly assigned 50 newborns who were at high risk of developing AD (1:1) to receive general infant skin-care advice (control group), or skin-care advice plus emollient with advice to apply emollient at least once daily until 1 year of age (intervention group). Repeated skin examinations, skin physiology measurements and skin microbiome profiling were performed. Of the children in the intervention and control groups, 28% and 24%, respectively, developed AD (adjusted Relative Risk (RR) 1.19, p = 0.65, adjusted risk difference 0.05). Skin pH decreased and transepidermal water loss and stratum corneum hydration increased over time in both groups with no significant differences. In the intervention group skin microbiome alpha diversity increased earlier, and the abundance of Streptococcus and Staphylococcus species were significantly reduced at month 1. Daily early emollient use in children with high risk of AD was safe, but it did not significantly reduce the risk of developing AD or impact skin physiology development.

Relationship Between Degree of Neonatal Physiologic Desquamation and Skin Barrier Function.

BACKGROUND/OBJECTIVES: This study examined the relationship between degree of neonatal physiologic desquamation and skin barrier functionality. In addition, we identified factors associated with neonatal desquamation. METHODS: This cross-sectional study assessed 4-day-old newborns. The desquamation level was evaluated and placed in one of the following categories based on the severity of the desquamation: no desquamation, a small amount, and severe (including cracked or bleeding). Skin barrier function was assessed by evaluating transepidermal water loss, stratum corneum hydration, skin pH, and sebum secretion. RESULTS: Among study participants, 67 (39.9%) showed no desquamation, 82 (48.8%) displayed a small amount, and 19 (11.3%) had severe desquamation. The group with severe desquamation had significantly elevated facial transepidermal water loss levels and reduced levels of stratum corneum hydration throughout the body, indicating skin barrier dysfunction, than other groups. In addition, the group with severe desquamation had a significantly longer gestational age, lower temperature and humidity level, smaller vernix caseosa, and tended to be born during winter. CONCLUSIONS: To our knowledge, this is the first report indicating that infants with severe desquamation had worsened skin barrier function versus those with moderate and no desquamation. Future research should consider what kind of care should be provided to newborns with severe desquamation.