Quantifying the mechanical behavior of skin has been foundational in applications of cosmetics, surgical techniques, forensic science, and protective clothing development. However, previous puncture studies have lacked consistent and physiological boundary conditions of skin. To determine natural skin tension, excision of in situ porcine skin resulted in significantly different diameter reduction (shrinkage) in leg (19.5 %) and abdominal skin (38.4 %) compared to flank skin (28.5 %) (p = 0.047). To examine effects of initial tension and pre-conditioning, five conditions of initial tension (as percentage of diameter increase) and pre-conditioning were tested in quasistatic puncture with a 5 mm spherical impactor using an electrohydraulic load frame and custom clamping apparatus. Samples with less than 5 % initial tension resulted in significantly greater (p = 0.011) force at failure (279.2 N) compared to samples with greater than 25 % initial tension (195.1 N). Eight pre-conditioning cycles of 15 mm displacement reduced hysteresis by 45 %. The coefficient of variance was substantially reduced for force, force normalized by cutis thickness, displacement, stiffness, and strain energy up to 46 %. Pre-conditioned samples at physiological initial tension (14-25 %) resulted in significantly greater (p = 0.03) normalized forces at failure (278.3 N/mm) compared to non-conditioned samples of the same initial tension (234.4 N/mm). Pre-conditioned samples with 14-25 % initial tension, representing physiological boundary conditions, resulted in the most appropriate failure thresholds with the least variation. For in vitro puncture studies, the magnitude of applied initial tension should be defined based on anatomical location, through a shrinkage experimentation, to match natural tension of skin. Characterizing the biological behavior and tolerances of skin may be utilized in finite element models to aid in protective clothing development and forensic science analyses.

In vivo mechanical characterization of skin finds broad applications in understanding skin aging, diagnosis of some skin diseases and assessing the effectiveness of diverse skin care strategies. Skin has a layered structure consisting of the epidermis, dermis and subcutaneous layers. Although much effort has been made towards mechanical characterization of skin, it remains a challenging issue to measure the mechanical properties of an individual layer in vivo. To address this issue, we here report a guided wave elastography method for layered human skin which incorporates the effect of muscle states. Both finite element simulations and phantom experiments have been performed to validate the method. For skin-mimicking phantoms with different fat layer thicknesses, the errors in the identified shear modulus of the skin layers are no more than 11 %. In vivo experiments have been carried out on 6 healthy subjects to demonstrate the potential use of the method in clinics. A statistical analysis indicates the muscle contraction contributes to the stiffening of the skin (p < 0.001). Finally, a phase diagram has been constructed to reveal the extent to which muscle sates (including both passive and active states) affect the measurement of elastic modulus of a skin layer, which may guide the application of the method in practice.

OBJECTIVE: While there are a wide range of approaches for the assessment of skin hydration, it is not always clear how data from them relate to one another or to the skin itself. With the development of in vivo Confocal Raman Spectroscopy (ICRS), it has become possible to measure water concentration as a function of protein/depth within the stratum corneum (SC). This article reports a comparison between electrical skin hydration measures/visual/optical grading and water concentration profiles measured using ICRS, to better understand the relationship between these approaches.
METHODS: SC hydration of lower-leg skin with varying degrees of dryness was assessed using visual grading (live and from digital images), Corneometer®, Visioscan and ICRS. In addition, a custom fingerprint sensor was used to image surface capacitance (as a surrogate of SC hydration), and SC barrier function was assessed using evaporimetry (to measure trans-epidermal water loss; TEWL).
RESULTS: Significant correlations were observed between a number of different skin grading/measurement approaches and ICRS data. ICRS hydration profiles also revealed a region near the SC surface with a relatively flat water profile in dry skin subjects.
CONCLUSIONS: The advent of quantitative in vivo analytical techniques such as ICRS, which can be used in a clinical setting, has enabled greater insight into more conventional approaches for assessing skin dryness. While traditional skin grading and biophysical methods for measuring skin hydration have varying degrees of correlation with one another, they also provide comparatively unique information about different regions within the SC. This should enable a more informed approach to product development in the future.
OBJECTIVE: Bien qu’il existe un large éventail d’approches pour évaluer l’hydratation de la peau, la façon dont les données qui en résultent sont liées les unes aux autres ou à la peau elle‐même n’est pas toujours claire. Avec le développement de la spectroscopie Raman confocale in vivo (ICRS), il est devenu possible de mesurer la concentration en eau en fonction du rapport protéine/profondeur au sein de la couche cornée (stratum corneum, SC). Cet article rapporte une comparaison entre les mesures électriques ou la classification visuelle/optique de l’hydratation de la peau et les profils de concentration en eau mesurés à l’aide de l’ICRS, afin de mieux comprendre la relation entre ces approches. MÉTHODES: L’hydratation du SC de la peau de la partie inférieure de la jambe avec différents degrés de sécheresse a été évaluée à l’aide d’une classification visuelle (en direct et à partir d’images numériques), du Corneometer®, du Visioscan et de l’ICRS. En outre, un capteur d’empreintes digitales personnalisé a été utilisé pour visualiser la capacité de surface (en tant que substitut de l’hydratation du SC) et la fonction de barrière du SC a été évaluée par évaporimétrie (pour mesurer la perte d’eau transépidermique ; trans‐epidermal water loss, TEWL). RÉSULTATS: Des corrélations significatives ont été observées entre un certain nombre d’approches différentes de classification/mesure de la peau et les données ICRS. Les profils d’hydratation de l’ICRS ont également révélé une région près de la surface du SC ayant un profil d’eau relativement plat chez les sujets atteints de sécheresse cutanée.
CONCLUSIONS: L’avènement de techniques d’analyse in vivo quantitatives telles que l’ICRS, qui peut être utilisée dans un contexte clinique, a permis de mieux comprendre les approches plus conventionnelles d’évaluation de la sécheresse cutanée. Bien que les méthodes traditionnelles de classification de la peau et les méthodes biophysiques de mesure de l’hydratation de la peau présentent des degrés de corrélation variables entre elles, elles fournissent également des informations comparativement uniques sur différentes régions au sein du SC. Cela devrait permettre une approche plus éclairée du développement de produits à l’avenir.

BACKGROUND: Stratum corneum (SC) is essential for skin barrier function, mitigating water loss and shielding against potentially harmful substances and allergens. The SC\'s lipid matrix, arranged in a lamellar structure, is integral to its protective role. Our study explores the restoration effects of a multilamellar cream with an acidic pH compared to a basic placebo cream on skin physiology and its interaction with the skin microbiome after stress induction via tape stripping (TS).
METHODS: In this double-blind study, 14 healthy participants aged 21-58 years were assessed pre- and post-tape stripping, followed by a 14 days application of a multilamellar test cream and a placebo cream with evaluations on days 7, 14 and 17 for sustained effects. Skin physiology was analysed in terms of epidermal barrier function, SC hydration and surface pH. The microbiome was analysed by 16S rRNA amplicon sequencing the 16S rRNA gene using Illumina MiSeq, with subsequent species identification.
RESULTS: Our study showed significant improvements in skin barrier repair and SC hydration with verum, particularly after 14 days of application, while both creams initially enhanced stratum corneum hydration. No significant changes in surface-pH were detected. The skin microbiome analysis revealed that TS slightly decreased alpha diversity, a trend that verum significantly reversed, enhancing diversity beyond baseline levels after 14 days. Overall, while both creams contributed to a broader microbial phyla diversity over time, no significant changes in the abundance of specific genera or species were noted between treatments.
CONCLUSIONS: Our study delineates the efficacy of a pH-optimized multilamellar cream in enhancing epidermal barrier recovery and SC hydration post-sequential TS, in contrast to an unstructured basic placebo. Verum cream significantly improved skin barrier function and SC hydration at day 14, with sustained effects evident beyond the treatment period. Furthermore, the multilamellar formulation facilitated the restitution of cutaneous microbiome diversity, a key indicator of healthy skin ecology, underscoring the symbiotic relationship between barrier integrity and microbial composition. These findings underscore the importance of multilamellar emollient structures in dermatological therapeutics, with potential implications for the design of advanced skincare interventions that holistically support cutaneous resilience and homeostasis.
BACKGROUND: La couche cornée (stratum corneum, SC) est essentielle pour la fonction de barrière cutanée, atténuant la perte d’eau et protégeant contre les substances et allergènes potentiellement nocifs. Disposée selon une structure lamellaire, la matrice lipidique de la SC est constitutive de son rôle protecteur. Notre étude explore les effets de restauration d’une crème multilamellaire à pH acide par rapport à une crème placebo de base sur la physiologie de la peau et son interaction avec le microbiome de la peau après induction de stress via un test tape stripping (TS). MATÉRIELS ET MÉTHODES: Dans cette étude en double aveugle, 14 participants en bonne santé âgés de 21 à 58 ans ont été évalués avant et après tape stipping, puis ont procédé à l’application pendant 14 jours d’une crème test multilamellaire et d’une crème placebo avec des évaluations aux jours 7, 14 et 17 pour les effets durables. La physiologie de la peau a été analysée en termes de fonction de la barrière épidermique, d’hydratation SC et de pH de surface. Le microbiome a été analysé par séquençage de l’amplicon de l’ARNr 16S sur le gène de l’ARNr 16S à l’aide d’Illumina MiSeq, avec identification ultérieure des espèces. RÉSULTATS: Notre étude a montré des améliorations significatives de la réparation de la barrière cutanée et de l’hydratation SC avec le traitement actif, en particulier après 14 jours d’application, tandis que les deux crèmes avaient initialement amélioré l’hydratation de la couche cornée. Aucun changement significatif du pH de surface n’a été détecté. L’analyse du microbiome cutané a révélé que le TS diminuait légèrement la diversité alpha, une tendance qui s’est significativement inversée avec le traitement actif : une amélioration de la diversité au‐delà des taux initiaux était observée après 14 jours. Dans l’ensemble, bien que les deux crèmes aient contribué à une plus grande diversité des phyla microbiennes au fil du temps, aucune variation significative dans l’abondance de genres ou d’espèces spécifiques n’a été observée entre les traitements.
UNASSIGNED: Notre étude délimite l’efficacité d’une crème multilamellaire à pH optimisé pour améliorer la réparation de la barrière épidermique et l’hydratation SC après un TS séquentiel, contrairement à un placebo basique non structuré. La crème contenant le traitement actif a significativement amélioré la fonction de barrière cutanée et l’hydratation SC au jour 14, avec des effets durables évidents au‐delà de la période de traitement. En outre, la formulation multilamellaire a facilité la restitution de la diversité du microbiome cutané, un indicateur clé d’une écologie de peau en bonne santé, soulignant la relation symbiotique entre l’intégrité de la barrière et la composition microbienne. Ces résultats soulignent l’importance des structures émollientes multilamellaires dans les traitements dermatologiques, avec des implications potentielles pour la conception d’interventions cutanées avancées qui soutiennent de manière holistique la résilience cutanée et l’homéostasie.

Anthony V. Rawlings has had 30+ years of experience in the general area of skin science. He has many scientific publications, and his work has been highly cited. He has made major contributions to our understanding of skin physiology, including xerosis and hydration, barrier function, desquamation, the corneocyte envelope, physical chemistry of stratum corneum lipids, photodamage and ethnic variation. He has held management positions with several companies in the US and UK, established AVR Consulting in 2002 and maintained a long-standing relationship with colleagues at University College London. His time as the Editor in Chief of the International Journal of Cosmetic Science was pivotal in the development of the journal. He worked hard and succeeded in getting the IJCS included in the PubMed database.
Anthony V. Rawlings a plus de 30 ans d\'expérience dans le domaine général de la science de la peau. Il est l\'auteur d\'un grand nombre de publications scientifiques, et ses travaux ont été largement cités. Il a beaucoup contribué à notre compréhension de la physiologie de la peau, notamment la xérose et l\'hydratation, la fonction de barrière, la desquamation, l\'enveloppe des cornéocytes, la chimie physique des lipides de la couche cornée, le photodommage et les variations ethniques. Il a occupé des postes de direction dans plusieurs entreprises aux États‐Unis et au Royaume‐Uni, a créé AVR Consulting en 2002 et entretient une relation de longue date avec ses collègues de l\'University College de Londres. Le temps qu\'il a passé comme rédacteur en chef de l\'International Journal of Cosmetic Science a été déterminant dans le développement de la revue. Il a travaillé dur et a réussi à faire inclure l\'IJCS dans la base de données PubMed.

BACKGROUND: Skin conditions in patients with lymphedema have been identified according to changes in skin mechanical properties. The skin elasticity meter is a non-invasive tool for measuring the mechanical properties of the skin; however, its potential use in patients with lymphedema has received little attention. This review aimed to provide an overview of studies measuring the skin mechanical properties of patients with lymphedema using a skin elasticity meter.
METHODS: Search terms and synonyms related to lymphedema and skin mechanical property measurement using a skin elasticity meter were identified, and electronic databases containing articles in English were searched.
RESULTS: A total of 621 articles were retrieved, and four articles were analyzed after screening. Despite this research subject receiving increasing attention, no consensus has been reached regarding the best methods.
CONCLUSIONS: Measurement methods are expected to be standardized in the future to elucidate the skin mechanical properties of patients with lymphedema.

BACKGROUND: Skincare and makeup \"pilling\" is an unsightly and undesirable phenomenon whereby skincare such as moisturizers or foundation ball up to form flakes on the skin. To date, the causes of skincare product pilling have not been studied. This study aimed to examine the relationship between skin physiology and pilling potential of sunscreen and foundation (the two products most reported by consumers to cause pilling). This study also examined the effects of product application methods on pilling.
METHODS: 528 female volunteers from Guangzhou, China, aged between 20 and 49 years, underwent various clinical skin assessments, followed by three steps of product layering. Pilling was assessed after each product application step.
RESULTS: 217 volunteers (41%) experienced pilling. The majority of pilling (n = 655 events) occurred following sunscreen application, while only a few pilling events (n = 35) occurred with foundation. Foundation improved pilling caused by sunscreen in 98.9% of cases. Volunteers experiencing pilling with both sunscreen and foundation had significantly lower facial skin hydration and oiliness, higher pH, and smoother skin texture (P < 0.05). Two application methods, rubbing of products in circular and linear motions, yielded the highest numbers of pilling events.
CONCLUSIONS: This study has provided the first insights into the causes of pilling. Sunscreen is a promoter of pilling, while foundation may resolve sunscreen-induced pilling in many cases. Skin physiology, particularly drier, smoother skin with higher pH, and product application methods are likely contributing factors to this undesirable phenomenon.

No other organ in the human body has as many functions as the skin-biologic, cultural, social, and psychologic. The skin is the first attribute we notice, and it is the basis of our first impressions. It provides information about our state of health, our moods, our age, and sometimes our cultural background. Above all, the skin is an organ like the heart or the lungs. The objective of this exploratory anthropologic study was to shed light on the people\'s global perception of the skin. More precisely, we wanted to explore how people think about their skin and whether they think of it in terms of its biologic role and importance as their body\'s largest organ. We wanted to know how aware they are about the skin\'s anatomy, functionality, and the pathologies that most concern them. Do people consider their skin merely as an envelope of beauty or as something more? To find out, we conducted a prospective anthropologic study of a random sampling of multicultural individuals in and around Paris, France. Participants were given a questionnaire with six semi-structured questions and one open-ended question about their per-ceptions and attitudes of their skin. Responses were analyzed on the basis of word groupings within the six major categories of considerations represented by the available literature on the skin in both French and English. The results of this study demonstrated the mutable nature of people\'s perception of their skin. Rather than remaining with one fixed vision, their thoughts about their skin changed in conjunction with their age, life experiences, and lifestyle in accordance with wider societal and environmental realities. In addition, their perspectives tended to go beyond cultural groupings, displaying a certain homogeneity of vision across demographic categories. As such, we concluded that the skin is a form of virtual reality that is constructed and reconstructed as one moves through life in the society.

This smooth flat experimental study investigates the capability of mako shark scales to control flow separation when placed downstream of the onset of turbulent boundary layer separation and within the reattachment region. The objective of the study is to validate the hypothesis that the shark scales\' bristling and recoiling would prevent the flow separation on the flank region (the fastest flow region) of the shark. A rotating cylinder was used to induce an adverse pressure gradient over a flat plate to produce a region of separated flow where the shark skin specimen was mounted. Two types of mako shark scales (flank (B2) and between flank and dorsal fin (B1)) were positioned in the preferred flow direction on a flat plate. The B2 scales are slender, 200μm tall, and can bristle up to 50°. In contrast, B1 scales are wider, shorter, and can bristle at 30°. The bristling angle and shape are the main mechanisms by which the scales act to inhibit flow from moving upstream near the wall. Thus, the difference in the bristling angles and structures of the scales is attributed to the fact that the B2 scales function in a thicker boundary layer (behind the shark\'s gills) where they must bristle sufficiently high into the boundary layer to control the flow separation, and because the adverse pressure gradient in this region is higher where flow separation is more likely. The scales are placed in the reattachment region to elucidate their ability to control and reattach an already separated turbulent flow. The results show that B2 scales placed in the reattachment region reduce the size of the turbulent separation bubble and decrease the turbulent kinetic energy, while B1 scales have the opposite effect.

The present work studies the variation in the nature of Rayleigh waves due to change in age, gender and morphological region of human skin tissue in the context of three-phase-lag (TPL) nonlocal thermoelastic theory. The secular equations are derived using the stress free, thermally insulated or isothermal boundary conditions. These secular equations are solved numerically and two significant modes of Rayleigh wave are noted to propagate simultaneously. The phase speeds, attenuation coefficients and path of the particle motion for both modes are presented graphically. These results are compared for different age, gender and morphological region of the source skin tissue. We have observed that the phase speeds increase with the increases of stiffness of the skin and vice versa. Certain specific angular frequencies and phase speeds are obtained which can be used for the detection and thermal therapy of skin disorders. Some published results are recovered as special cases to validate the current results.