Bioengineering and subjective approaches to the clinical evaluation of dry skin

Dry skin (also known as xerosis) is a cutaneous reaction pattern indicative of abnormal desquamation, which has not only cosmetic considerations, but can also lead to the penetration of irritants and allergens through the stratum corneum (SC). Over the last few decades, our understanding of the structure, composition, formation and function of the SC has advanced tremendously; however, despite these advancements, the occurrence of dry skin remains prevalent in the adult population. The clinical evaluation of dry skin is therefore of significant importance to the cosmetic industry not only for understanding the condition but also for measuring the effects of treatment. Traditionally, dry skin has been evaluated by visual inspection, however, recently a variety of bioengineering techniques have emerged enabling the investigator to objectively assess the extent of xerotic conditions. The most frequently employed methods for the evaluation of dry skin are discussed in this review, including regression testing, squametry, measurement of transepidermal water loss, epidermal hydration, profilometry, confocal Raman spectroscopy, optical coherence tomography, in vivo confocal microscopy and magnetic resonance imaging.     

The regulatory role of the tetrapeptide AcSDKP in skin and hair physiology and the prevention of ageing effects in these tissues – a potential cosmetic role

The naturally occurring tetrapeptide acetyl‐N‐Ser‐Asp‐Lys‐Pro (AcSDKP) recognized as a potent angiogenic factor was shown recently to contribute to the repair of cutaneous injuries. In the current article, we report the ability of AcSDKP to exert a beneficial effect on normal healthy skin and scalp and to compensate for the ageing process. In vitro AcSDKP at 10^?11–10^?7 M significantly stimulates the growth of human keratinocytes, fibroblasts and follicle dermal papilla cells. Moreover, it enhances the growth of human epidermal keratinocyte progenitor and stem cells as shown in a clonogenic survival assay. Topical treatment of ex vivo cultured skin explants with 10^?5 M AcSDKP increases the thickness of the epidermis and upregulates the synthesis of keratins 14 and 19, fibronectin, collagen III and IV as well as the glycoaminoglycans (GAGs). In the ex vivo‐cultured hair follicles, AcSDKP promotes hair shaft elongation and induces morphological and molecular modifications matching the criteria of hair growth. Furthermore, AcSDKP at 10^?11–10^?7 M was shown to improve epidermal barrier, stimulating expression of three protein components of tight junctions (claudin‐1, occludin, ZO‐1) playing an important role in connecting neighbouring cells. This tetrapeptide exercises also activation of SIRT1 implicated in the control of cell longevity. Indeed, a two‐fold increase in the synthesis of SIRT1 by cultured keratinocytes was observed in the presence of 10^?11–10^?7 M AcSDKP. In conclusion, these findings provide convincing evidence of the regulatory role of AcSDKP in skin and hair physiology and suggest a cosmetic use of this natural tetrapeptide to prevent skin ageing and hair loss and to promote the cutaneous regeneration and hair growth.     

Increased basal transepidermal water loss leads to elevation of some but not all stratum corneum serine proteases

There are indications of elevation of some inflammatory serine proteases in barrier damaged skin (e.g. plasmin and urokinase). Moreover, many other serine protease activities are present such as desquamatory enzymes as well as a newly detected tryptase‐like serine protease. However, the activities of these proteases have never been correlated with stratum corneum (SC) barrier function. The activity of extractable key serine proteases (SC trypsin‐like kallikreins, SC chymotrypsin‐like kallikreins, SC tryptase‐like serine protease, urokinase and plasmin) was measured from the outermost layers of SC obtained from facial tape strippings in clinically normal subjects. The protein content of the tape strippings was quantified by absorption measurements with the novel infrared densitometer SquameScan^TM 850A and the protease activities by the use of fluorogenic peptide substrates. SC barrier function, SC hydration and skin surface pH were measured using AquaFlux^TM, NOVA dermal phase meter and Skin‐pH‐Meter^®, respectively. As expected, SC hydration was reduced with increased transepidermal water loss (TEWL) values indicative of barrier impairment. Surprisingly, SC chymotrypsin‐like activity showed no correlation with hydration or TEWL, whereas all other enzymes positively correlated with impaired barrier function and some were statistically significant: SC trypsin‐like kallikreins (R² = 0.66, P < 0.01), SC tryptase‐like enzyme (R² = 0.95, P < 0.001), plasmin (R² = 0.86, P < 0.001) and urokinase (R² = 0.50, P < 0.05). All enzymes except urokinase also negatively correlated with SC hydration. Elevated levels of SC serine proteases have been associated with some dermatological disorders, such as atopic dermatitis, psoriasis and rosacea but these results indicate that these enzymes are also elevated with milder forms of barrier disruption, which is not clinically evident as irritated skin. As these proteases are elevated in the SC, they will also be elevated in the epidermis where they can be involved in neurogenic inflammation and epidermal barrier impairment via activation of the protease‐activated receptors. These results highlight the need for using serine protease inhibitors especially for urokinase and plasmin, SC tryptase‐like serine protease and possibly SC trypsin‐like kallikreins even in milder forms of barrier damage.     

Location‐related differences in structure and function of the stratum corneum with special emphasis on those of the facial skin

Between the two different kinds of the skin covering the body, the glabrous skin is found only on the palmo‐plantar surface because of its rather simple function to protect the underlying living tissue with its remarkably thick stratum corneum (SC) from strong external force and friction. Thus, its barrier function is extremely poor. In contrast, the hair‐bearing skin covers almost all over the body surface regardless of the presence of long hair or vellus hair. In regard to its SC, many dermatologists and skin scientists think that it is too thin to show any site‐specific differences, because the SC is just present as an efficient barrier membrane to protect our body from desiccation as well as against the invasion by external injurious agents. However, there are remarkable regional differences not only in the living skin tissue but also even in such thin SC reflecting the function of each anatomical location. These differences in the SC have been mostly disclosed with the advent of non‐invasive biophysical instruments, particularly the one that enables us to measure transepidermal water loss (TEWL), the parameter of the SC barrier function, and the one that evaluates the hydration state of the skin surface, the parameter of the water‐holding capacity of the SC that brings about softness and smoothness to the skin surface. These in vivo instrumental measurements of the SC have disclosed the presence of remarkable differences in the functional properties of the SC particularly between the face and other portions of the body. The SC of the facial skin is thinner, being composed of smaller layers of corneocytes than that of the trunk and limbs. It shows unique functional characteristics to provide hydrated skin surface but relatively poor barrier function, which is similar to that observed in retinoid‐treated skin or to that of fresh scar or keloidal scars. Moreover, there even exist unexpected, site‐dependent differences in the SC of the facial skin such as the forehead, eyelid, cheek, nose and perioral regions, although each location occupies only a small area. Between these locations, the cheek shows the lowest TEWL in contrast to the perioral region that reveals the highest one. Moreover, these features are not static but change with age particularly between children and adults and maybe also between genders. Among various facial locations, the eyelid skin is distinct from others because its SC is associated with poor skin surface lipids and a thin SC cell layer composed of large corneocytes that brings about high surface hydration state but poor barrier function, whereas the vermillion borders of the lips that are covered by an exposed part of the oral mucosa exhibit remarkably poor barrier function and low hydration state. Future studies aiming at the establishment of the functional mapping in each facial region and in other body regions will shed light on more delicate site‐dependent differences, which will provide us important information in planning the strategy to start so called tailor‐made skin care for each location of the body.     

Cinnamic acid derivatives in cosmetics: current use and future prospects

Cinnamic acid derivatives are widely used in cosmetics and possess various functions. This group of compounds includes both naturally occurring and synthetic substances. On the basis of the Cosmetic Ingredient Database (CosIng) and available literature, this review summarizes their functions in cosmetics, including their physicochemical and biological properties as well as reported adverse effects. A perfuming function is typical of many derivatives of cinnamaldehyde, cinnamyl alcohol, dihydrocinnamyl alcohol and cinnamic acid itself; these substances are commonly used in cosmetics all over the world. Some of them show allergic and photoallergic potential, resulting in restrictions in maximum concentrations and/or a requirement to indicate the presence of some substances in the list of ingredients when their concentrations exceed certain fixed values in a cosmetic product. Another important function of cinnamic acid derivatives in cosmetics is UV protection. Ester derivatives such as ethylhexyl methoxycinnamate (octinoxate), isoamyl p‐methoxycinnamte (amiloxiate), octocrylene and cinoxate are used in cosmetics all over the world as UV filters. However, their maximum concentrations in cosmetic products are restricted due to their adverse effects, which include contact and a photocontact allergies, phototoxic contact dermatitis, contact dermatitis, estrogenic modulation and generation of reactive oxygen species. Other rarely utilized functions of cinnamic acid derivatives are as an antioxidant, in skin conditioning, hair conditioning, as a tonic and in antimicrobial activities. Moreover, some currently investigated natural and synthetic derivatives of cinnamic acid have shown skin lightening and anti‐ageing properties. Some of them may become new cosmetic ingredients in the future. In particular, 4‐hydroxycinnamic acid, which is currently indexed as a skin‐conditioning cosmetics ingredient, has been widely tested in vitro and in vivo as a new drug candidate for the treatment of hyperpigmentation.     

Evaluation of the efficacy of a dill extract in vitro and in vivo

Lysyl oxidase–like (LOXL) is an extracellular enzyme that catalyses the cross‐linking between microfibrils and tropoelastin (TE), thereby ensuring elastic fibre functionality. With ageing, LOXL expression decreases, thus participating in the loss of skin elasticity. In a previous study, we showed that a dill seed extract [INCI name: Peucedanum graveolens (Dill) extract] could increase LOXL expression in cultured dermal fibroblasts. Besides, we showed a good correlation between the measurements of skin elasticity obtained in vitro and in vivo using a fully automated bio‐tribometer designed to measure the biomechanical properties of soft and complex materials like skin. The aim of this study was to evaluate the ability of the dill extract to improve skin elasticity in vitro and in vivo using different models. Using the bio‐tribometer, we first showed that the lateral elasticity of dermis equivalents (DEs) treated with the dill extract at 1% was significantly increased by +29% (P < 0.01) when compared to untreated DEs. In vivo, skin firmness and elastic recovery measured using cutometry methods were also significantly improved compared to placebo in volunteers treated for 56 days with a formula containing 1% of dill extract. Moreover, the clinical evaluation evidenced significant improvements in ‘skin elasticity’ compared to placebo. A majority of subjects treated with the dill extract also noted significant improvements in skin elasticity, firmness and slackness of the jaw line. Finally, mean wrinkle area and length were also significantly reduced compared to placebo after 84 days as measured using silicone replicas taken from the crow’s feet. In summary, this study showed that the dill extract could improve elasticity of DEs in vitro as well as skin biomechanical properties and appearance in vivo. It also highlights the relevance of using the bio‐tribometer as an exploratory tool for the measurement of skin elasticity in vitro.     

In vivo barrier challenge and long‐term recovery in human facial skin

Recently, we developed a biophysical approach to characterize in vivo facial cheek skin as a function of stratum corneum (SC) depth, barrier function and during a 24‐h recovery period. The current study extends this work and characterizes the human facial cheek after barrier challenge and, for the first time, facial SC barrier recovery over a 4‐week period. Changes in the corneocyte size over the 4‐week recovery period, and correlations with changes in Trans‐Epidermal Water Loss (TEWL) were monitored. This approach allows complete characterization of SC barrier function after a full biological regeneration of the SC barrier following tape stripping. The structural and compositional changes in facial cheek were investigated using Attenuated Total Reflectance‐Fourier Transform Infra Red (ATR‐FTIR) spectroscopy, tape stripping, TEWL measurements and image analysis combined with optical microscopy to characterize the SC depth profile during the tape stripping stress and over 4‐week recovery period. TEWL increased significantly from baseline after sequential tape stripping. Corneocyte size decreased with successive tape stripping. An inverse direct correlation was determined between TEWL and corneocyte surface area. After 4 weeks, the corneocyte size and TEWL for the facial cheek recovered 100% from the tape stripping procedure. The in vivo ATR‐FTIR data demonstrated that lipid and sebum components on the surface of the facial cheek SC recovered within 24 h post tape stripping, whereas protein (Amide II) and water components recovered after 1 week.     

Singlet molecular oxygen quenching by the antioxidant dimethylmethoxy chromanol in solution and in ex vivo porcine skin

Singlet‐oxygen is a non‐radical reactive oxygen species believed to play a major role in many photooxidation processes in connection with diverse photo‐biological processes such as skin ageing or photocarcinogenesis. Dimethylmethoxy chromanol (3,4‐dihydro‐6‐hydroxy‐2,2‐dimethyl‐7‐methoxy‐1(2H)‐benzopyran) is a potent antioxidant used in cosmetic and pharmaceutical formulations. We have assessed the singlet oxygen quenching ability of dimethylmethoxy chromanol, by monitoring the near‐IR phosphorescence of singlet‐oxygen in solution and in ex vivo porcine skin samples. Dimethylmethoxy chromanol quenches singlet oxygen with a rate constant of (1.3 ± 0.1) × 10⁸ M^?1 s^?1 in solution. Consistent with this, a clear reduction in the singlet oxygen lifetime and emission intensity was observed when ex vivo porcine skin samples were treated with dimethylmethoxy chromanol.     

Oxidization of squalene,a human skin lipid: a new and reliable marker of environmental pollution studies

A review of the oxidization of squalene, a specific human compound produced by the sebaceous gland, is proposed. Such chemical transformation induces important consequences at various levels. Squalene by‐products, mostly under peroxidized forms, lead to comedogenesis, contribute to the development of inflammatory acne and possibly modify the skin relief (wrinkling). Experimental conditions of oxidation and/or photo‐oxidation mechanisms are exposed, suggesting that they could possibly be bio‐markers of atmospheric pollution upon skin. Ozone, long UVA rays, cigarette smoke… are shown powerful oxidizing agents of squalene. Some in vitro, ex vivo and in vivo testings are proposed as examples, aiming at studying ingredients or products capable of boosting or counteracting such chemical changes that, globally, bring adverse effects to various cutaneous compartments.     

Relationship between perceived softness of bilayered skin models and their mechanical properties measured with a dual‐sensor probe

The development of a sensor system that can predict the subjective softness of human skin is an important goal for the cosmetics industry. Here, we first carried out a subjective softness evaluation test using 65 skin models consisting of polyurethane bilayers with different thickness of the superficial layer and different degree of cross‐polymerization of the basal layer. The results showed that perceived softness was dependent on the mechanical properties of both the superficial and basal layers. Then, we used a recently developed tactile sensor system composed of a piezoelectric tactile sensor and a load cell to measure mechanical softness parameters of the superficial layer and the whole model, respectively. Statistical analysis showed that the data obtained from these two sensors were well correlated with the perceived softness of the prepared models. These results suggest that it may be feasible to predict the subjective softness of human skin in vivo from non‐invasive mechanical softness measurements of the superficial skin layer and whole skin obtained with our new dual‐probe sensor system.     

Biophysic evaluation of polysaccharide gel from durian’s fruit hulls for skin moisturizer

Durian or Dutio zibethinus Murr. (Bombacaceae) is a tropical fruit native to Southeast Asia particularly cultivated in Thailand as an economic plant. Once it is consumed, the fruit hulls are discarded as waste products. Polysaccharide gel (PG) from durian’s fruit hulls is obviously efficient for use in the preparations of food and pharmaceutical products. This research focused on biophysical assessment of PG durian’s fruit hulls for cosmetic formulation. The efficacy of facial skin capacitance and firmness increment of PG formulation were evaluated. Its application showed significant effect on skin capacitance after 28 and 56 days (P = 0.024 and P = 0.003) and significantly increased skin firmness after 56 days of treatment (P = 0.017) with non‐allergic effect as there were no positive patch tests.     

Skin cell targeting with self‐assembled ligand addressed nanoemulsion droplets

Dermo‐pharmacy and cosmetic industries have utilized nanotechnologies for two decades. Initially proposed as vector systems for encapsulation of actives, they gained interest in increasing cutaneous bioavailability. Here, we assay the benefits of self‐assembled nanoemulsions bearing ligands for targeting specific skin cells. Nanoemulsions, small droplets ranging typically from 20 nm to 150 nm, possess key properties for further use in cosmetics: long‐term stability, optical transparency, extended range of textures and versatility. We investigated this nanoemulsion system and show ability to encapsulate a range of cosmetic actives with various physicochemical properties. Furthermore, this nanoemulsion presents a low cytotoxicity and is capable of directly targeting skin cells through simple addition of specific ligand in a one‐step production protocol. This is of interest for increasing bioavailability of actives encapsulated into nanoemulsion droplets which may have penetrated the skin barrier to specific skin cell. Taken together, these chemical and in vitro observations suggest follow‐up with in vivo models.     

The role of sodium dodecyl sulfate (SDS) micelles in inducing skin barrier perturbation in the presence of glycerol

The stratum corneum (SC) serves as the skin barrier between the body and the environment. When the skin is contacted with an aqueous solution of the surfactant sodium dodecyl sulfate (SDS), a well‐known model skin irritant, SDS penetrates into the skin and disrupts this barrier. It is well established, both in vitro and in vivo, that the SDS skin penetration is dose‐dependent, and that it increases with an increase in the total SDS concentration above the critical micelle concentration (CMC) of SDS. However, when we added the humectant glycerol at a concentration of 10 wt% to the aqueous SDS contacting solution, we observed, through in vitro quantitative skin radioactivity assays using ¹⁴C‐radiolabeled SDS, that the dose dependence in SDS skin penetration is almost completely eliminated. To rationalize this important observation, which may also be related to the well‐known beneficial effects of glycerol on skin barrier perturbation in vivo, we hypothesize that the addition of 10 wt% glycerol may hinder the ability of the SDS micelles to penetrate into the skin barrier through aqueous pores that exist in the SC. To test this hypothesis, we conducted mannitol skin permeability as well as average skin electrical resistivity measurements in vitro upon exposure of the skin to an aqueous SDS contacting solution and to an aqueous SDS + 10 wt% glycerol contacting solution in the context of a hindered‐transport aqueous porous pathway model of the SC. Our in vitro studies demonstrated that the addition of 10 wt% glycerol: (i) reduces the average aqueous pore radius resulting from exposure of the skin to the aqueous SDS contacting solution from 33 ± 5Å to 20 ± 5Å, such that a SDS micelle of radius 18.5 ± 1Å (as determined using dynamic light‐scattering measurements) experiences significant steric hindrance and cannot penetrate into the SC, and (ii) reduces the number density of aqueous pores in the SC by more than 50%, thereby further reducing the ability of the SDS micelles to penetrate into the SC and perturb the skin barrier.     

Chemical analysis and photoprotective effect of an extract of wine from Jacquez grapes

The present study was aimed at evaluating the in vitro antioxidant activity and in vivo photoprotective activity of an extract of wine obtained from Jacquez (Vitis aestivalis‐cinerea × V vinifera) grapes (JW‐E). The chemical profile of the JW‐E was characterised by a significant level of proanthocyanidins, together with lower amounts of anthocyanins and hydroxycinnamic acids. The antioxidant activity of the JW‐E was assessed by means of various in vitro tests (bleaching of the stable 1,1‐diphenyl‐2‐picrylhydrazyl radical; peroxidation, induced by the water‐soluble radical initiator 2,2′‐azobis(2‐amidinopropane) hydrochloride, on mixed dipalmitoylphosphatidylcholine/linoleic acid unilamellar vesicles; UV radiation‐induced peroxidation in phosphatidylcholine multilamellar vesicles). In all in vitro tests employed, the JW‐E proved to possess strong antioxidant/free radical‐scavenging effectiveness. Furthermore, when topically applied, a gel formulation containing the JW‐E afforded significant in vivo protection against UVB light‐induced skin erythema (monitored by reflectance spectrophotometry) in healthy human volunteers. © 2002 Society of Chemical Industry     

On the effects of a plant extract of Orthosiphon stamineus on sebum‐related skin imperfections

Overproduction of sebum is very common and results in an undesirable oily, shiny complexion with enlarged pores. Sebum secretion is basically under the control of 5‐α reductase, and more particularly under that of type 1 isozyme. But it is also highly sensitive to environmental factors such as temperature, humidity and food. Moreover, in Asia, the edicts of a flawless facial skin turn oily skin into a major concern for Asian women. We identified Orthosiphon stamineus leaf extract as an interesting ingredient for reducing the oily appearance of skin thanks to its ability to reduce 5‐α reductase type 1 expression in normal human epidermal keratinocytes in vitro. This was confirmed ex vivo, where Orthosiphon stamineus leaf extract was shown to reduce 5‐α reductase activity as well as the production of squalene, one of the main components of sebum that was used as a tracer of sebum. To evaluate the efficacy of Orthosiphon stamineus leaf extract at reducing sebum‐related skin imperfections in vivo, we performed two different clinical studies, one in France on a panel of Caucasian volunteers and the other one in Thailand on a panel of Asian volunteers. Using instrumental techniques as well as clinical evaluation and self‐evaluation, we could highlight that an O/W cosmetic formula containing 2% of Orthosiphon stamineus leaf extract could visibly reduce the oily appearance of skin as well as the size of pores, thus leading to a significant improvement of complexion evenness and radiance. Overall, the results obtained were better than those observed with the same formula containing 1% of zinc gluconate, an ingredient frequently used in oily skin care products.     

Distinct locational differences observable in biophysical functions of the facial skin: with special emphasis on the poor functional properties of the stratum corneum of the perioral region

The face is composed of complicated anatomical components, presenting unique portions, such as the eyes, nose and mouth in a relatively narrow area. Moreover, the facial skin is densely populated by the pilosebaceous units and sweat glands, and its stratum corneum (SC) is much thinner than that of the trunk and limbs, although it is always exposed to the environment. Among various portions of the facial skin, some are more easily irritated than others by environmental stimuli, or are more often affected by certain dermatoses. However, the functional aspects of the different portions of the facial skin have not been studied in detail under a strictly controlled environment in sufficiently large numbers of subjects covering different age groups. Thus, we conducted studies in winter with various biophysical techniques, such as transepidermal water loss (TEWL), as a parameter for SC barrier function, high-frequency conductance as that for skin surface hydration state, skin surface lipids, pH, blood flow and skin surface temperature on the forehead, mid-portion of the cheek (cheek in short), nasal tip (nose in short), nasolabial fold and chin of 20 healthy Japanese females aged 22-37 years (average 25 years) in a climate chamber adjusted to 21 degrees C and 50% relative humidity. Thereafter, we studied the influence of ageing on these biophysical parameters by collecting data of TEWL, high-frequency conductance and size of superficial corneocytes on the cheek, nasolabial fold and chin of 303 healthy Japanese female volunteers of different ages. The obtained results showed that the barrier function of the SC was best on the cheek, presenting the lowest TEWL, which was significantly higher on the nasolabial fold and chin than on the cheek. TEWL showed a decrease with age. In contrast, skin hydration state was higher on the nose, but it tended to be lower on the nasolabial fold, showing a mild age-related increase. The corneocytes on the nasolabial fold and chin were smaller than those on the cheek. They revealed a clear increase in size with age. Skin surface lipids were richest on the nose, whereas the superficial pH on the nose was the lowest among the regions tested. The skin temperature was lowest on the cheek than on other areas of the face; although, together with the nose, its blood flow was higher than that of the others. These data indicate great regional differences observable in SC functions on the face. In general, the SC barrier function increases with age, probably because of a decreased epidermal turnover rate as recognized by the increase in corneocyte size. Among the various sites, the skin of the nasolabial fold and chin, whose SC consisted of the smallest corneocytes, showed poorest SC properties in barrier function, suggesting the presence of mild invisible inflammation. It is understandable that this area easily develops not only the complaint of sensitive skin to cosmetics but also dermatitis because of various external agents.     

J. Cosmet. Sci., 59, 263–289 (July/August 2008)Visualization and quantification of skin barrier perturbation induced by surfactant–humectant systems using two-photon fluorescence microscopy

In order to visualize the effects of aqueous surfactant–humectant systems on the skin barrier, an in vitro two‐photon fluorescence microscopy (TPM) study, including dual‐channel visualization, was carried out. TPM is a non‐invasive imaging technique based on two‐photon induced nonlinear excitations of fluorophores, with the capability for deep‐tissue imaging (up to several hundred micrometers). The following aqueous solutions of surfactants, a humectant, and a surfactant + humectant mixture that contacted pig full‐thickness skin (p‐FTS) were studied: (i) a harsh surfactant solution—sodium dodecyl sulfate (SDS) (1 wt%); (ii) a harsh surfactant + humectant solution—SDS (1 wt%) + glycerol (10 wt%); (iii) a mild surfactant solution—sodium cocoyl isethionate (SCI) (1 wt%); (iv) a control solution—phosphate‐buffered saline (PBS); and (v) a humectant solution—glycerol (10 wt%). Sulforhodamine B (SRB), a hydrophilic fluorescent probe, was used to visualize the effects of aqueous contacting solutions i–v on the skin barrier morphology. The results of the TPM visualization study revealed that SDS induces corneocyte damage by denaturing keratins and creating intracorneocyte penetration pathways. On the other hand, SDS + glycerol did not significantly induce corneocyte damage. The dual‐channel TPM images corresponding to aqueous contacting solutions iii–v showed low SRB penetration into the corneocytes, as well as localization of the SRB probe within the lipid bilayers surrounding the corneocytes of the SC. Through a quantification of the amount of SRB that penetrated into the skin as a function of skin depth, we found that adding glycerol to an SDS aqueous contacting solution can significantly reduce the SDS‐induced penetration depth of SRB, which provides evidence of the ability of glycerol to mitigate SDS‐induced skin barrier perturbation. The distribution of SRB in the p‐FTS samples was analyzed using a theoretical model that quantified changes in the skin aqueous pore characteristics induced by aqueous contacting solutions i, ii, iii, and v, relative to aqueous contacting solution iv, the control. The results of the theoretical model indicate the following ranking order in the extent of perturbation to the skin aqueous pores (from the highest to the lowest): i > ii > iii > iv > v. The development of such an in vitro visual ranking methodology, including quantification using TPM, can potentially reduce many costly in vivo screening procedures, thereby significantly reducing the cost and time‐to‐market of new cosmetic formulations containing surfactants and humectants.     

Multipotentiality of skin-derived precursors: application to the regeneration of skin and other tissues

Skin-derived precursors (SKPs) have been described as multipotent dermal precursors. Here, we provide a review of the breadth and depth of scientific literature and studies regarding SKPs, accounting for a large number of scientific publications. Interestingly, these progenitors can be isolated from embryonic and adult skin, as well as from a population of dermal cells cultured in vitro in monolayer. Gathering information from different authors, this review explores different aspects of the SKP theme, such as the potential distinct origins of SKPs in rodents and in humans, and also their ability to differentiate in vitro and in vivo into multiple lineages of different progeny. This remarkable capacity makes SKPs an interesting endogenous source of precursors to explore in the framework of experimental and therapeutic applications in different domains. SKPs are not only involved in the skin’s dermal maintenance and support as well as wound healing, but also in hair follicle morphogenesis. This review points out the interests of future researches on SKPs for innovative perspectives that may be helpful in many different types of scientific and medical domains.     

Instrumental and clinical studies of the facial skin tone and pigmentation of Shanghaiese women. Changes induced by age and a cosmetic whitening product

The pigmentation patterns of facial skin of 354 healthy Chinese women aged 18–80 years were investigated clinically and instrumentally. Chromasphere^® was used to acquire pictures from the cheeks of subjects. Facial skin tone was described by L* parameter from the L,a,b system as well as Individual Typology Angle (ITA). Results show that skin tone becomes significantly darker along the life span. Both size of hyper‐pigmented spots and their contrast with surrounding skin were found increased with age. As additional study, 40 women from these 354 subjects were asked to apply daily a whitening cosmetic product for a 2‐month period. Such application led to a significantly lighter skin tone, although this study was not vehicle controlled and we cannot exclude that the increase in L* observed was in some part because of cumulative effects of previously used whitening products, there was an association with lighter skin tone as assessed through both instrumental measurements and self‐perception by most subjects.     

Oral fish cartilage polysaccharides in the treatment of photoageing: biophysical findings

The topically applied cosmetic products can be helpful in improving the aged skin condition. The present study shows how oral fish-cartilage food supplementation can be helpful in improving the treatment of ageing skin. A total of 30 healthy women with signs of skin ageing were studied. Fifteen of the women were treated with a food supplement based on polysaccharides derived from the fish cartilage and a natural mix of antioxidants for 2 months and the other 15 with a placebo. Clinical evaluation and biophysical parameters related to skin function and wrinkle severity, such as silicone replica, skin thickness, mechanical properties, skin colour and capacitance, were measured. The results showed statistically significant changes in the active-treated group in comparison to the placebo. In particular, dermal thickness (treatment: from 1.13 to 1.23 mm; P < 0.001), skin wrinkling (treatment: from 9.5 to 3.5 R(a); P< 0.002), skin colour (treatment: brighter and less pigmented; P < 0.02) and viscoelasticity (treatment: from 0.70 to 0.97%; P < 0.02) showed considerable improvement. Most of these parameters are related to changes occurring within the dermal matrix, which is improved after the treatment, whereas most of the topically applied cosmetic products have a short-term effect on superficial structures. A combination treatment (oral and topical) can be more effective in reducing the signs of skin-ageing.