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We previously showed that the adult ocellated lizard skin colour pattern is effectively generated by a stochastic cellular automaton (CA) of skin scales. We additionally suggested that the canonical continuous 2D reaction-diffusion (RD) process of colour pattern development is transformed into this discrete CA by reduced diffusion coefficients at the borders of scales (justified by the corresponding thinning of the skin). Here, we use RD numerical simulations in 3D on realistic lizard skin geometries and demonstrate that skin thickness variation on its own is sufficient to cause scale-by-scale coloration and CA dynamics during RD patterning. In addition, we show that this phenomenon is robust to RD model variation. Finally, using dimensionality-reduction approaches on large networks of skin scales, we show that animal growth affects the scale-colour flipping dynamics by causing a substantial decrease of the relative length scale of the labyrinthine colour pattern of the lizard skin.

Background: Autologous lipografting for improvement of facial skin quality was first described by Coleman in 2006. The current dogma dictates that adipose tissue-derived stromal cells that reside in the stromal vascular fraction of lipograft contribute to skin rejuvenation (e.g., increased skin elasticity), a more homogenous skin color, and softening of skin texture. Nowadays, many studies have been reported on this "skin rejuvenation" effect of autologous fat grafting. This systematic review was undertaken to assess the efficacy of autologous lipografting on skin quality., Methods: The MEDLINE, Embase, Cochrane Central, Web of Science, and Google Scholar databases were searched for studies evaluating the effect of autologous lipografting on facial skin quality (May 11, 2018). Outcomes of interest were skin texture, color, and elasticity in addition to histologic outcomes and number of complications., Results: Nine studies were included, with 301 patients treated in total. No meta-analysis could be performed because of heterogeneity of the metrics and outcomes. Eight studies reported increased skin elasticity; improvement in skin texture; and a more homogeneous skin color after treatment with lipografting, cellular stromal vascular fraction, or nanofat. One study reported no increased skin elasticity after lipografting. Histologic improvement was seen after lipografting and adipose tissue-derived stromal cell injections. However, in general, the level of evidence of the included studies was low. No serious complications were reported., Conclusion: Autologous facial lipografting and cellular stromal vascular fraction and adipose tissue-derived stromal cell injections hardly seem to improve facial skin quality but can be considered a safe procedure.

Objective: Skin biomechanics are physical properties that protect the body from injury. Little is known about differences in skin biomechanics in racial/ethnic groups and the role of skin color in these differences. The purpose of this study was to determine the relationship between skin biomechanics (viscoelasticity, hydration) and skin color, when controlling for demographic and health-related variables in a sample of Puerto Rican and non-Puerto Rican women., Methods: We performed a secondary analysis of data from 545 women in a longitudinal, observational study of skin injury in Puerto Rico and the United States. Data included measures of skin viscoelasticity, skin hydration, skin color, demographic, and health related variables. Skin color was measured by spectrophotometry (L* - lightness/darkness, a*- redness/greenness, b* - yellowness/blueness). The sample was 12.5% Puerto Rican, 27.3% non-Puerto Rican Latina, 28.8% Black, 28.6% White, and 2.8% Other., Results: Regression analyses showed that: 1) higher levels of skin viscoelasticity were associated with lower age, higher BMI, and identifying as non-Puerto Rican Latina as compared to Puerto Rican; (all p < .001); and 2) higher levels of hydration were associated with lower L* values, higher health status, lower BMI, and identifying as non-Puerto Rican Latina, White, or Other as compared to Puerto Rican (all p < .05)., Conclusion: When adjusting for skin color, Puerto Rican women had lower viscoelasticity and hydration as compared to other groups. Puerto Rican women may be at long-term risk for skin alterations, including pressure injury, as they age or become chronically ill.

Purpose: A series of studies suggest that non-Hispanic White women have significantly more injuries than non-Hispanic Black women after sexual assault and consensual sexual intercourse. One explanation for this difference is that the degree of skin protection may vary as skin mechanics and skin pigmentation vary. The aim of the study was to determine the association among genital-anal injury, skin color, skin viscoelasticity and skin hydration in women following consensual sexual intercourse when controlling for age, smoking history, body mass index (BMI), sun exposure, and health status., Procedures: We employed a prospective cohort study design to enroll women 21 years of age or older at two study sites. They underwent two data collection sessions, baseline and follow-up after consensual sexual intercourse. Baseline genital-anal injury identification occurred with a standard forensic examination (direct visualization, nuclear staining with toluidine blue contrast, and colposcopy examination) and measurements of other variables (skin color, skin viscoelasticity, skin hydration, age, smoking history, body mass index [BMI], sun exposure, and health status). Participants were then asked to have consensual sexual intercourse with a male partner of their choice and to return for a second forensic examination for injury detection. Genital-anal injury was regressed on skin color, skin viscoelasticity, skin hydration, age, smoking history, BMI, sun exposure, and health status., Findings: We enrolled 341 participants, 88 non-Hispanic White (25.8%), 54 non-Hispanic Black (15.8%), 190 Hispanic/Latina (55.7), and 9 Other Identities (2.6%). At baseline the genital-anal injury prevalence was 57.77% and at follow-up after consensual sexual intercourse, injury prevalence was 72.73%. External genital injury prevalence was associated with increased L* (lightness) values (Adjusted Odds Ratio [AOR] = 1.98, 95% Confidence Interval [CI] = 1.03, 4.04) and decreased skin elasticity (AOR = 0.96, 95% CI = 0.93, 0.99) at baseline. Increased skin hydration was associated with a significantly higher frequency of external, internal, anal, and total genital-anal injuries (Adjusted Rate Ratio [ARR] > 1.27) at follow-up. Also at the follow-up examination, Hispanic/Latina participants had significantly lower external genital and total genital-anal injury prevalence and frequency as compared to non-Hispanic White participants (AOR < 0.40)., Conclusions: Our findings provide qualified support for the importance of skin color during the forensic examination. Women with lighter skin tones may have skin that is more easily injured than women with darker tones. In contrast, external genital injuries may be more easily identified in women with light as compared to dark skin, a situation that is important in both the health care and criminal justice systems. Additionally, women with decreased viscoelasticity and increased hydration may be more easily injured. These findings support the need to develop forensic procedures that are effective in people across the range of skin colors and to interpret forensic findings considering the innate properties of the skin., (Copyright © 2019 Elsevier Ltd and Faculty of Forensic and Legal Medicine. All rights reserved.)

Like many highly variable human traits, more than a dozen genes are known to contribute to the full range of skin color. However, the historical bias in favor of genetic studies in European and European-derived populations has blinded us to the magnitude of pigmentation's complexity. As deliberate efforts are being made to better characterize diverse global populations and new sequencing technologies, better measurement tools, functional assessments, predictive modeling, and ancient DNA analyses become more widely accessible, we are beginning to appreciate how limited our understanding of the genetic bases of human skin color have been. Novel variants in genes not previously linked to pigmentation have been identified and evidence is mounting that there are hundreds more variants yet to be found. Even for genes that have been exhaustively characterized in European populations like MC1R, OCA2, and SLC24A5, research in previously understudied groups is leading to a new appreciation of the degree to which genetic diversity, epistatic interactions, pleiotropy, admixture, global and local adaptation, and cultural practices operate in population-specific ways to shape the genetic architecture of skin color. Furthermore, we are coming to terms with how factors like tanning response and barrier function may also have influenced selection on skin throughout human history. By examining how our knowledge of pigmentation genetics has shifted in the last decade, we can better appreciate how far we have come in understanding human diversity and the still long road ahead for understanding many complex human traits., (© 2018 American Association of Physical Anthropologists.)

Background: Several terms have been used to characterize skin types. However, these are not based on evident dermatologic definitions, which usually include subjective and psychological properties., Objective: The objective of this study is to establish a new practical questionnaire to classify skin subtypes in Korean women to establish treatment and skin care guidance., Methods: Eight experts developed consensus statements about skin types and created a questionnaire. The content was categorized into four major subtypes: dry or non-dry; oily or nonoily; sensitive or nonsensitive; and pigmented or nonpigmented. A total of 512 patients completed the questionnaire. Correlations with age, skin Fitzpatrick's phototypes, and dermatologic comorbidities were analyzed., Results: Korean women commonly have oily skin but complain of dryness after cleansing. They are especially sensitive to skin care products and prone to developing pigmentary lesions. There was a trend in the proportion of dry skin subtype that increased as pigmented skin increased and oily skin decreased with advanced age. The proportion of sensitive skin was higher in patients with dermatologic comorbidities. The proportion of the pigmented skin was higher in darker Fitzpatrick skin phototypes., Conclusion: This is the first questionnaire established for Korean women to classify practical skin subtypes and may provide a basis for treating various skin conditions.

Background: Facial threading involves the removal of hairs to restore facial skin smoothness. However, its effectiveness has not been rigorously evaluated., Objective: To evaluate effects of facial threading on skin roughness, hydration, melanin index, and vellus hair on the face, complemented by a subjective evaluation of the tactile feel of the skin and improvement in skin color., Method: Participants who had not used exfoliators for two weeks before the experiment were included. Each participant underwent one session of facial threading every 21 days, for a total of 3 sessions. A three-dimensional skin roughness instrument and a multifunctional skin testing system were used to evaluate changes in roughness, hydration, and pigmentation on the forehead, cheeks, and corners of the mouth. A photomicrographic camera was used to record changes in vellus hair. Subjective reports of skin smoothness and color were recorded., Result: Eighteen participants completed the study. Facial threading produced a significant decrease in skin roughness on the forehead (22.42%, p = .013), right cheek (77%, p = .02), and left corner of the mouth (33.02%, p = .001). Subjective improvement in tactile feel of the skin and coloring were reported., Study Limitations: The study did not include randomization, with further limitations of a small sample size and a single site., Conclusion: Facial threading reduced skin roughness by 26.74% after three threading sessions, with improved subjective assessment of tactile feel and coloring. Future research should include a comparison with other cosmetic products with similar beautifying effects or a control group.

Background: Newborn infant skin changes after birth but studies have focused on the epidermal barrier. Dermal properties are relevant for care, but literature on postnatal changes is sparse. We further characterized skin maturational changes in lightness, color and response to biomechanical stress., Methods: Normal skin sites from subsets of participants in a trial on the progression and stage of infantile hemangiomas were retrospectively examined. Standardized photographs were analyzed as L*, a*, and b* images. Biomechanics were measured with the Cutometer ® ., Results: Color changed significantly with increasing age. Skin was darker and redder at 2.0 vs. 5.4, 8.5 and 12.8 months. Yellow color increased, with higher values at 12.8 vs. 2.0, 3.5 and 5.4 months. Chest tissue was consistently more elastic than arm and face sites, with significantly higher elasticity for the youngest and oldest age groups. Biological elasticity, elastic recovery, and total recovery were significantly greater for the oldest subjects. Viscoelasticity and elastic deformation were lower at 5.5 vs. 8.8 and 17.6 months. Arm viscoelastic creep was highest at 2.8 months., Conclusion: Skin maturation continues into year two. Increasing elasticity and decreasing viscoelasticity may reflect increased collagen structure/function. The findings have implications for prevention of skin injury associated with mechanical forces., (© 2017 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

The primary cilium is an organelle protruding from the cell body that senses external stimuli including chemical, mechanical, light, osmotic, fluid flow, and gravitational signals. Skin is always exposed to the external environment and responds to external stimuli. Therefore, it is possible that primary cilia have an important role in skin. Ciliogenesis was reported to be involved in developmental processes in skin, such as keratinocyte differentiation and hair formation. However, the relation between skin pigmentation and primary cilia is largely unknown. Here, we observed that increased melanogenesis in melanocytes treated with a melanogenic inducer was inhibited by a ciliogenesis inducer, cytochalasin D, and serum-free culture. However, these inhibitory effects disappeared in GLI2 knockdown cells. In addition, activation of sonic hedgehog (SHH)-smoothened (Smo) signaling pathway by a Smo agonist, SAG inhibited melanin synthesis in melanocytes and pigmentation in a human skin model. On the contrary, an inhibitor of primary cilium formation, ciliobrevin A1, activated melanogenesis in melanocytes. These results suggest that skin pigmentation may be regulated partly by the induction of ciliogenesis through Smo-GLI2 signaling., Competing Interests: All authors declare that they have no competing interests relating to employment, consultancy, patents, products in development or marketed products.

Background/purpose: The skin contains an undulating structure called the dermal papillary structure between the border of the epidermis and dermis. The physiological importance of the dermal papillary structures has been discussed, however, the dermal papillary structures have never been evaluated for their contribution to skin appearance. In this study, we investigated the correlation between the dermal papillary structure and skin color and elasticity. In addition, the relationship was validated with skin model experiments., Methods: The dermal papillary structures in the skin of the female cheek were quantitatively measured by in vivo confocal laser scanning microscopy images. In addition, the skin color and elasticity were measured at the same site. A skin model with dermal papilla-like structures was created by referring to the optical and shape properties of the skin using agar gel and a scattering sheet., Results: Correlations were found between the dermal papillary structures and skin color irregularity and skin elasticity. These relationships were verified by the experiments employing a skin model., Conclusion: The results of this study indicated that the dermal papillary structure is also an important factor for skin appearance such as color and elasticity., (© 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Background/aims: The age-dependent changes in the optical reflection characteristics have been studied about skin hydration, melanin index, or skin color. However, the age-dependent changes in the optical reflection have little attention on inner skin structures. To control the factors affecting the optical reflection except for dermal matrix, subjects were selected as our guideline and we evaluated the optical reflection of subsurface on skin layers of two age groups., Method: Young and old healthy volunteers were recruited after signing a written informed consent form. Facial skin was measured by means of noninvasive measurements: skin hydration, color, epidermis and dermis thickness, dermal density, subsurface reflectance, and transmittance., Result: Compared to young group, old group showed that dermal density and thickness was decreased significantly although epidermis thickness was not changed., Conclusion: In conclusion, dermal density is one of the major factors which affects the subsurface reflectance in skin., (© 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Little is known about nonpathological facial skin problems at present. The aim of the present study was to investigate the relationships among facial skin conditions, mood, and the fatty acid composition of red blood cells (RBCs) in women. One hundred and thirty-two apparently healthy Japanese women aged between 20 and 60 years were recruited. Facial skin conditions were analyzed using a Robo Skin Analyzer, and the RBC fatty acid composition was also determined. Questionnaires concerning mood were administered. Forehead pigmentation was more mood-dependent (in 20s group) and less arachidonic acid (AA)-dependent (in all participants) than that in other areas of the face. Actually there was no correlation in pigmentation between the forehead and other areas of the face when adjusted for age, smoking, and drinking. Skin conditions were adversely correlated with a negative mood. α-Linolenic acid concentrations were negatively correlated with negative mood scores. Pigmentation characteristics in the forehead were independent from other areas of the face. Negative mood and AA were adversely correlated with skin conditions.

This paper studies the formation of the large dark patterns, known as parr marks, that form on the Amago trout as it grows from the early larval stages to adulthood. The Amago trout, known as Oncorhynchus masou ishikawa, exhibits stripes during the early stages of development that in turn evolve (through reorientation and peak insertion) to form zigzag spot patterns as the fish grows to adulthood. By considering a standard representation of the Turing model for biological self-organization via interacting and diffusing morphogens, we illustrate that a diffusively driven instability can generate transient patterns consistent with those experimentally observed during the process of parr-mark formation in the early development of the Amago trout. Surface evolution is modeled through an experimentally driven growth function. Our studies conclude that the surface evolution profile, the surface geometry, and the curvature are key factors that play a pivotal role in reaction-diffusion systems in a study motivated by observations of Amago trout parr-mark pattern formation.

Knowledge of the optical properties of neonatal skin is invaluable when developing new, or improving existing optical techniques for use at the neonatal intensive care. In this article, we present in vivo measurements of the absorption μ(a) and reduced scattering coefficient μ(s) (') of neonatal skin between 450 and 600 nm and assess the influence of age and skin pigmentation on the optical properties. The optical properties were measured using a spatially resolved, steady state diffuse reflectance spectroscopy setup, combined with a modified spatially resolved diffusion model. The method was validated on phantoms with known values for the absorption and reduced scattering coefficient. Values of μ(a) and μ(s) (') were obtained from the skin at four different body locations (forehead, sternum, hand, and foot) of 60 neonates with varying gestational age, postnatal age, and skin pigmentation. We found that μ(a) ranged from 0.02 to 1.25 mm(-1) and μ(s) (') was in the range of 1 to 2.8 mm(-1) (5th to 95th percentile of the patient population), independent of body location. In contrast to previous studies, no to very weak correlation was observed between the optical properties and gestational maturity, but a strong dependency of the absorption coefficient on postnatal age was found for dark skinned patients.

Background: Scaling skin involves an imbalance between cell proliferation and desquamation, resulting in partially detached corneocytes at the stratum corneum (SC) surface that become visible as they scatter light., Objectives: The purpose of this study was to document scaling skin with no associated pathology, to estimate the range of normal corneocyte detachment in the average population, and to determine if age, pigmentation and/or body sites of different exposures contribute to differences observed in the SC., Methods: Healthy African-American and Caucasian female subjects (n = 151) from a typical central New Jersey population, aged between 14 and 75 years, were evaluated on the dorsal forearm and upper inner arm. Dermatoscopy and adhesive tape were used to evaluate the appearance and adhesion of surface corneocytes. Transepidermal water loss and conductivity were measured to assess water-handling properties of the SC. Measurements were conducted during the winter., Results: Corneocyte detachment observed with dermatoscopy became more prevalent with age and was more severe on the dorsal forearm and in Caucasian subjects. The distribution of the amount of corneocyte removal with adhesive tape increased with age. The range of values was larger in the dorsal forearm than the upper inner arm and was greater in Caucasian subjects than African-American subjects. Minimal changes were observed for water-handling properties., Conclusions: The architecture of the outer SC appears different between ages, body sites of different exposures, and individuals of different pigmentation groups, but minimal differences in water-handling properties are observed., (© 2011 The Authors. BJD © 2011 British Association of Dermatologists.)

The measurement and quantification of skin reactions to insults involves certain assumptions about the relation between intensity of color appearance of the skin and the concentration of endogenous chromophores. The underlying assumption is that the Beer-Lambert law is obeyed, i.e., that a linear relation exists between the absorbance and the concentration of each chromophore and that the total absorbance is the linear superposition of the contributions of each chromophore. In this paper the authors compiled the results from a number of interventions on human skin that result in changes in its appearance and small deviations from the homeostatic state, where the results may be accounted for by a single or multiple chromophores. The validity of the assumptions is found to hold for a limited range of responses. The biological constraints need to be considered in certain cases because as we move away from the homeostatic state, complex biological processes are induced., (2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Background: Various physical, chemical and biological insults, including exposure to ultraviolet (UV) radiation, cause erythema and change in pigmentation in human skin. These reactions provide an important measure of the cutaneous response to the insult., Objectives: To present a new implementation of a method for objective in vivo measurement of erythema and pigmentation., Methods: The method is based on acquisition of reflectance spectra in the visible range using a commercially available spectrophotometer. The probe of this instrument incorporates an integrating sphere that captures the light remitted from the skin in a wide range of angles. We corrected the acquired reflectance spectra for the contribution of specular reflections by an amount given by the Fresnel equation and verified this correction experimentally. This correction is particularly important when measurements are performed on heavily pigmented skin. The corrected reflectance spectra are then transformed into absorbance spectra. To analyse these spectra, we developed an algorithm which can be used to calculate apparent concentrations of oxyhaemoglobin, deoxyhaemoglobin and melanin. This method was tested in clinical studies of skin reactions induced by exposure to UV radiation. These experiments involved three groups of subjects with progressively darker complexion (constitutive pigmentation). Each group consisted of 10 subjects. Erythema was measured 1 day after UV exposure, and pigmentation (melanin content) 1 week later. Results Distinct apparent absorbance spectra were obtained for dark, intermediate and fair skin. There was good agreement between reconstructed spectra and experimental data at relevant wavelengths. Difference absorption spectra were able to show the dose dependence of UV-induced responses, and erythema and pigmentation values obtained by the spectroscopic method showed good correlation with those derived by subjective visual grading., Conclusions: The results demonstrate that the presented methodology provides an objective noninvasive way of measuring UV-induced reactions independently of the level of constitutive pigmentation.

Glycation is the non-enzymatic reaction between reducing sugars and proteins that leads to the formation of advanced glycation end products (AGEs). In vivo skin autofluorescence (lambda(ex)/lambda(em)=370/440 nm) was used as a non-invasive clinical tool to study skin AGE accumulation in healthy panellists. Using multiple linear regression analysis, it was shown that for panellists below the age of 40, glycation associated in vivo skin fluorescence intensity increased as a function of chronological age and body mass index (BMI). Above the age of 40, the fluorescence was associated to age but not to BMI, suggesting that the effect of age became dominant over BMI. Since the accumulation of AGEs is expected to affect the biomechanical properties of the skin, in vivo skin elasticity data were gathered on a second panel. It was found that skin elasticity depended on age and BMI in a similar fashion as to what we observed for the skin fluorescence data. It is hypothesised that skin AGE accumulation contributes to the loss of skin elasticity in aged and/or overweight people.

The study aimed to establish solarium operators' compliance with a newly revised voluntary code for the industry in 2002. The revisions incorporate guidelines to ensure customers are adequately informed of the risks associated with solarium use and that access by high-risk groups, such as customers with fair skin that does not tan (skin type 1) or those less than 18 years of age, is limited or barred. Compliance tests with the industry standard were conducted at 30 solarium centres in Melbourne, Australia. Compliance was tested by surveys and in-person visits from three research assistants, each presenting as potential customers but with different eligibility to attend a sunbed session: young adults eligible to attend a solarium, young adults with skin type 1 and under-age (16 year old) customers. This is the first study to assess solarium compliance using confederates with customer profiles that correspond to the required restrictions on sunbed access. Results showed poor compliance with specific aspects of the voluntary code. Fifty-two per cent of centres gave the underage teenagers access to sunbeds without written parental consent. Ninety per cent of centres provided sunbed access to clients with poor tanning ability and 75% of centres tried to reassure them about using the sunbeds. Seven per cent of centres did not provide any form of eye protection for customers and 7% provided sub-standard stickers for eye protection. The study suggests that there is much room for improvement in solarium centres' current practices and further regulation may well be warranted.

Backgrounds/aims: The aim of the study was to compare the changes of the biophysical properties and to objectify the effects of 595 nm pulsed dye, 1064 nm Q-switched Nd:YAG and 1320 nm Nd:YAG lasers non-ablative rejuvenation by non-invasive techniques., Methods: KM mice were used for the study. The 595 nm pulsed dye, 1064 nm Q-switched Nd:YAG and 1320 nm Nd:YAG laser treatments were evaluated with biophysical parameter measurements including skin elasticity, skin color, skin trans-epidermal water loss (TEWL) and skin hydration., Results: All three lasers improved the biophysical properties in the skin of KM mice. In skin elasticity measurements, the 1064 nm laser treatment showed the lowest ratio (0.61+/-0.09) while the 1320 nm laser showed the highest one (0.76+/-0.07) on day 60. For erythema values, a significant increase was observed immediately after the 1064 nm laser treatment (196.67+/-19.17), but the lowest values occurred with the 1320 nm laser treatment (189.83+/-16.54). None of the three lasers resulted in obvious changes of skin melanin. TEWL increased immediately after laser irradiation, then began to recover and decreased 60 days after the 595 and 1064 nm laser treatments. With the 1320 nm laser treatment the TEWL began to decrease from day 7 and obtained the lowest mean values (5.23+/-1.13). The water-holding capacity increased initially for the 595 and 1320 nm laser irradiation, while decreased for the 1064 nm laser. At day 60 of the experiment, skin hydration values in all animals were superior to those of the controls. The 1320 nm laser treatment caused the highest ratio (1.29+/-0.26). Both the values of TEWL and skin hydration for the 1320 nm laser treated areas differed significantly from the other two lasers., Conclusions: Our data showed the 1064 nm Q-switched Nd:YAG laser treatment was most effective in improving the skins' mechanical properties, while the 1320 nm Nd:YAG laser can enhance greatly the skin barrier function and the water-holding capacity. Moreover, we demonstrated the biophysical properties differed considerably between different areas.

Sun exposure has been known to cause histological changes in the dermal layer of the skin. Using deterioration in the fine reticular patterning of the epidermal stratum corneum (skin pattern, as measured on the Beagley-Gibson scale) as a proxy measure of histological changes in the dermal layer, previous studies have typically assumed that degradation of skin pattern is largely caused by sun exposure. A twin study comprising 332 monozygotic twin pairs and 488 dizygotic twin pairs at ages 12, 14, and 16 was used to investigate the etiology of variation in skin pattern, particularly in relation to measured sun exposure and skin color. Our results indicate that although self-reported sun exposure is a significant contributor to variation in skin pattern, its effect is small, explaining only 3.4% of variation in skin pattern at age 14. Additive genetic effects explain 86% of variation in skin pattern at age 12 but these effects reduce with age so that 75% of variation is due to additive genetic effects at age 14 and 72% at age 16. This trend of diminishing genetic influences continues into adulthood, with 62% of variation due to non-additive genetic factors in a smaller adult sample (aged 32-86). Skin color explains 10.4% of variation in skin pattern at age 12, which is due to additive genetic influences common to both. Melanin content appears to provide a protective effect against skin pattern deterioration, perhaps because of the structural differences in melanosomes between different skin types or the free radical scavenging properties of melanin.

Ethnic (racial) differences exist for a series of physiological skin characteristics. Colour is responsible for typology and resistance to ultraviolet irradiations. Other differences have also been reported for the transepidermal water loss, the size and cohesion of corneocytes, the vascular reactiviy, the biomechanical properties, the pH, the lipidic content, the superficial microflora and the structure of mast cell granules.

A method to specifically ablate melanocytes in a genetically tractable organism would facilitate the analysis of melanocyte regeneration and regulation. We have demonstrated that a Q-switched neodymium:yttrium-aluminum-garnet dermatology laser kills larval melanocytes in zebrafish. Following melanocyte ablation, new melanocytes regenerate from unpigmented precursors. We show that melanocyte regeneration following laser ablation requires kit receptor tyrosine kinase.

A NATURAL PHENOMENON: Pregnancy is a period of hormone, immunological, metabolic and vascular changes. Modifications of the skin, mucosa and integuments are therefore physiological. The modifications are in pigmentation, but also affect nevi, the connective tissue, vessels and appendices. Modifications in pigmentation exist in more than 9 pregnancies out of 10 in the form of local melanosis. Melasma, also know as the 'pregnancy mask' or chloasma, is fairly rare. These disorders in pigmentation are also observed in black-skinned women. Changes in nevi (darker brown colour, increase in size) occur in around 15% of pregnancies. MODIFICATIONS IN CONNECTIVE TISSUE: Characterised by vergetures, affecting 60 to 90% of women, appear between the 6th and 8th month of pregnancy and for which there is no satisfactory treatment. Vascular modifications are generally proliferative and due to estrogen impregnation that affects the arteriolar and venous systems. Stellar angiomas are present in 50 to 70% of Caucasian women. Bilateral palmar erythema may also be associated with these angiomas. Varicose veins and varicosities of the lower limbs induced by excessive venous pressure are frequent, as well as oedema (salt-water retention, increased capillary permeability). MODIFICATIONS IN THE APPENDICES: These concern the activity of the sweat glands, the size of the sebaceous glands (Montgomery tubercles), the nails and hair growth.

There is still extensive disparity in our understanding of how estrogens exert their actions, particularly in non-reproductive tissues such as the skin. Although it has been recognized for some time that estrogens have significant effects on many aspects of skin physiology and pathophysiology, studies on estrogen action in skin have been limited. However, estrogens clearly have an important function in many components of human skin including the epidermis, dermis, vasculature, hair follicle and the sebaceous, eccrine and apocrine glands, having significant roles in skin aging, pigmentation, hair growth, sebum production and skin cancer. The recent discovery of a second intracellular estrogen receptor (ERbeta) with different cell-specific roles to the classic estrogen receptor (ERalpha), and the identification of cell surface estrogen receptors, has provided further challenges to understanding the mechanism of estrogen action. It is now time to readdress many of the outstanding questions regarding the role of estrogens in skin and improve our understanding of the physiology and interaction of steroid hormones and their receptors in human skin. Not only will this lead to a better understanding of estrogen action, but may also provide a basis for further interventions in pathological processes that involve dysregulation of estrogen action.

Epidemiological studies have suggested that UV exerts a protective effect on prostate cancer. Accordingly, we determined, in 210 prostate cancer cases, whether parameters of exposure, skin type and polymorphism in MC1R, VDR and TYR were associated with the outcome parameters, histological grade, clinical stage and presence of bone metastases. We used logistic regression analysis, with correction for age and metastases, stage and grade in the models, to determine if the frequencies of individual factors were different in the patient groups. The development of metastases was not associated with UV exposure parameters. Paradoxically, patients with skin type 1 were at significantly reduced risk [P = 0.027, odds ratio (OR) 0.17, 95% CI 0.03-0.82] of developing metastases compared with cases with skin type 4. MC1R Val92/Val92 and VDR ff were associated with increased risk of metastases (ORs 4.30 and 4.98, respectively). Further, cumulative exposure (P = 0.005, OR 0.85/year) and increasing proportion of outdoor occupation (P = 0.001, OR 0.84/unit) were associated with reduced risk of advanced stage tumours. Skin types, MC1R or VDR genotypes were not significantly associated with advanced stage. None of the exposure parameters, skin types or genotypes were associated with tumour grade. While MC1R Val92/Val92 and VDR ff were only associated with bone metastases, TYR genotypes were associated with each of the outcome parameters. Thus, in logistic regression models that included age, but not advanced stage and high grade histology, TYR A1A2 was significantly associated with reduced risk of metastases (P = 0.033, OR 0.41). Similarly, in models that included age but not the other outcome parameters, associations between TYR A2A2 and high-grade and advanced stage were significant (P = 0.040, OR 0.41) or approached significance (P = 0.052, OR 0.44), respectively. These data indicate for the first time that pigmentation response to UV is associated with outcome in prostate cancer.

In the human epidermis both keratinocytes and melanocytes express POMC m-RNA. Immunohistochemical studies of both cell types demonstrate significantly higher levels of alpha-MSH in melanocytes than in keratinocytes. Both cell types also hold the full capacity for de novo synthesis/recycling of the essential cofactor (6R)-L-erythro-5,6,7,8-tetrahydrobiopterin (6BH4). 6BH4 is critical for the hydroxylation of the aromatic amino acids L-phenylalanine, L-tyrosine, and L-tryptophan, for nitric oxide production and in various immune modulatory processes. Recently it was shown that tyrosinase activity is regulated by 6BH4 through a specific allosteric inhibition. The tyrosinase/6BH4 inhibition can be activated by 1:1 complex formation between 6BH4 and alpha-MSH, but an excess of alpha-MSH over 6BH4 can inhibit tyrosinase due to complex formation by tyr2 in the alpha-MSH sequence. In both melanocytes and keratinocytes 6BH4 controls the L-tyrosine supply via phenylalanine hydroxylase (PAH). Recently we were able to show that the cellular uptake of L-phenylalanine and its intracellular turnover to L-tyrosine is crucial for melanogenesis. alpha-MSH can promote the production of L-tyrosine via PAH due to activation of the PAH tetramer to the more active dimer by removing 6BH4 from the regulatory binding domain on the enzyme. In conclusion, alpha-MSH can control (1) intracellular L-tyrosine formation from L-phenylalanine in both melanocytes and keratinocytes, and (2) tyrosinase activity, directly, in melanocytes.

alpha-MSH, has numerous actions in the skin and by activating the MC1 receptor (MC1-R) on melanocytes it stimulates melanogenesis. Rather than producing large increase in melanin production alpha-MSH acts specifically to stimulate eumelanin synthesis. Although this could be important in determining skin color and tanning there is debate as to the pigmentary significance of alpha-MSH in humans. Circulating levels of alpha-MSH are negligible and although it is produced in the skin by different cell types, including melanocytes, the major skin form is desacetyl alpha-MSH, and this is a weak agonist at MC1-R. Certain ACTH peptides, notably ACTH1-17, are more potent agonists at the MC1-R and, since their skin concentrations exceed those of alpha-MSH, they could serve as natural ligands at this receptor and regulate pigmentary responses in humans. Activation of MC1-R does, however, produce other responses in human melanocytes. Thus, alpha-MSH stimulates melanocyte dendricity and attachment to extracellular matrix proteins. It also protects melanocytes from the damaging effects of oxidative stress, and regulates their production of NO by modulating the induction of iNOS--as it does within macrophages. alpha-MSH clearly affects various aspects of melanocyte behavior and its melanogenic effects could be the consequence of a more fundamental role in the melanocyte. The precise nature of this role is unclear, but it could be part of a generic role that alpha-MSH and other POMC peptides have in skin homeostasis.

Reproductive data are presented for female Papio papio housed in the Zoological Park of Paris and are compared with previously published data from free-ranging populations of other baboon species. The results indicate similar intermenstrual intervals and durations of sexual swelling. Sexual swelling and pregnancy are accelerated in captivity, while postpartum amenorrhea and interbirth interval are reduced. Interbirth intervals in P. papio were short, approximately 13 months in the case of viable, surviving infants and approximately 11 months in the case of stillbirth or neonatal mortality. The shorter interval may represent the lower physiological limit, and the generally shorter interbirth interval reported here may be explained by lower stress and reduced maternal investment costs in the captive environment. Paracallosal skin color variations during the menstrual cycle were influenced by parity, but sexual swelling patterns were not. The paracallosal skin changes might be used by males as a cue to females' reproductive status.

Sensitive skin has been described as a skin type showing higher reactivity than normal skin and developing exaggerated reactions when exposed to external factors. The stinging test, performed by applying lactic acid to the nasolabial fold and evaluating the intensity of subjective symptoms, is widely accepted as a marker of sensitivity and employed for the selection of subjects experiencing invisible cutaneous irritation. However, this test is based on self-perceived assessment and lacks objectivity. In order to contribute to the finding of objective descriptors, we assessed baseline biophysical parameters in subjects with sensitive skin by means of transepidermal water loss (TEWL), capacitance, pH, sebum and skin colour measurements, and compared the data with those obtained in normal subjects, also correlating the results with those of clinical assessments and functional tests. Subjects with sensitive skin showed a trend towards higher scores at all assessment times both for the stinging and the washing test. The skin of sensitive subjects was described as less supple, less hydrated and more erythematous and telangiectatic with respect to the skin of normal subjects. A trend towards an increase in TEWL, pH and colorimetric a* values, and a decrease in capacitance, sebum and colorimetric L* values on the face of subjects with sensitive skin was observable. However, significances were only present for capacitance and a* values. Thus, alterations of baseline capacitance values indicate the tendency to barrier impairment and support the view that skin hyperreactivity to water-soluble irritants is induced by a greater amount of irritants absorbed, whereas the increase in the erythema parameter shows that cutaneous vascular hyperreactivity in subjects with sensitive skin also corresponds to baseline vasodilation.

Melanoma risk differs by sun-sensitive phenotype, of which self-reported skin type (tendency to burn, inability to tan) is an indicator. If self-reports of skin type are influenced by the amount of sun exposure subjects have had, the two principal determinants of risk are linked, and stratifying by skin type would bias the estimated effect of sun exposure. Our objective was to determine whether teenagers changed their self-reports of skin type after being sunburnt. A random sample (n = 364) of 14-15 year old schoolchildren of northern European ancestry self-assessed and self-reported their skin type before and after their summer holidays. Their responses had high correlation coefficients (girls 0.71, boys 0.54) for repeatability at 4 months, but subjects who sunburnt less (more) frequently than usual that summer revised their skin type assessment to be less (more) sun-sensitive afterwards. We conclude that these 14-15 year olds were influenced by a recent experience of sunburn when reporting their skin type. A more objective measure of phenotype is needed.

Urocanic acid (UCA) is a major chromophore for UV in the skin and has been suggested to act as an initiator of UV-induced immunosuppression. It converts from the naturally occurring trans-isomer to the cis-isomer on UV exposure. Isomerization is dose dependent until the photostationary state is reached, and the seasonal variation in irradiance from the sun may lead to changes in the percentage of UCA present as cis-UCA throughout the year. Thirty young healthy subjects, skin types I-IV, were followed from early summer till spring. At each of six visits (June, July, August, October, December, March), pigmentation and the concentration of UCA isomers were measured at six body sites: forehead, upper chest, upper back, outer upper arm, inner upper arm and buttock. In exposed as well as unexposed regions a variation in pigmentation was found, peak values being recorded in August. Total UCA concentration was lower in July and August than in the rest of the year, irrespective of body site. In July, the percentage of cis-UCA was close to the maximal obtainable (50-60%) at all sites except the buttock. In the three winter months the percentage of cis-UCA was below 7% in all regions except for the forehead, where the mean cis-UCA was 18% in October and March. No consistent relationship was found between UCA isomers and pigmentation or skin type.

The Irish are generally considered to have a fair complexion. We surveyed the distribution of skin type in an Irish city population (n = 1000). Skin type prevalence was as follows: type 1: 26%, type 2: 49.6%, type 3: 19.7%, type 4: 4.3%, type 5: 0.3%, type 6: 0.1%. Sunbeds were used by 16% of the population. Malignant melanoma occurred in 1.4% of patients, non-melanoma skin cancer in 6%. The high frequency of sunbed use in a fair skinned population and the high incidence of skin cancer is disturbing and highlights the need for ongoing public health education regarding ultraviolet radiation risks.

Skin pigmentation is a physiological feature of great value and usefulness from both an anthropological point of view and a clinical point of view. This article is a first approach to the study of the skin pigmentation of 126 full-term newborn infants (37-42 weeks gestational age) at the Maternity Hospital "La Paz" (Madrid, Spain) using the reflectance method. We provide the normal patterns, which have to be taken into account when applying this method to detect transcutaneous bilirubin and some physiopathological conditions, such as hyperbilirubinemia, anemia, plethora, and hormonal disturbances. Measurements of the reflectance were taken at the forehead, the internal and external aspects of the arm, the thorax, and the gluteus with blue, green, and amber tristimulus filters. With all filters the least pigmented zone was the thorax, and the most pigmented zone was the forehead; the internal aspect of the arm, the gluteus, and the external aspect of the arm were intermediate in increasing order. Our data confirm a higher pigmentation at birth than during the first year. We think that the idea of cephalocaudal progression of hyperbilirubinemia must be rejected. Our results also indicate that the thickening of the skin with gestational age is one of the most important factors in the skin color changes of newborn infants with an apparently different rhythm in males than in females.

Pro-opiomelanocortin (POMC) is the precursor of ACTH, alpha-MSH and beta-endorphin, neuropeptides with multiple regulatory functions. Both the pituitary gland and peripheral tissues such as mammalian skin are capable of generating POMC-derived neuropeptides. Mammalian skin is also a target for POMC products; their possible roles in skin physiology and pathology are discussed in this communication.

A key question in the area of spatial pattern formation in developmental biology is: how do groups of cells in a homogeneous tissue suddenly differentiate along entirely different developmental paths compared to neighbouring cells? Although experiments are now beginning to provide answers to this question, the mechanisms responsible for the development of repeated or periodic structures and spatial patterns, e.g., hair follicles and pigmentation patterns, are still unknown. Theoretical biologists and applied mathematicians have suggested various prepattern mechanisms as the primary cause of repeated or periodic spatial patterns. A class of biochemical reactions referred to here as reaction-diffusion (RD) systems, having the capacity to spontaneously generate stable stationary wavelike spatial patterns (Turing, 1952), has been suggested as a possible prepattern mechanisms, e.g., during hair follicle initiation and development (Nagorcka, 1989), and pigmentation patterns (Murray, 1989). Spatial patterns arising during development of the vertebrate skin are frequently complex. Spatial patterns in the skin can be seen to vary within an individual from one region of the skin to another. One pattern change commonly observed across the skin is from stripes to spots. An RD system is defined which is able to generate different spatial patterns depending on the value of a single parameter. The parameter varied controls the transport of the chemical components of the RD system across the basement membrane separating the epidermis and dermis. The patterns produced range from stripes to an irregular array of spots. Not only are different patterns produced, but a different time sequence of prepatterns is expected to arise in the different skin regions depending on whether the first prepattern in an array of spots or stripes. As a consequence it is possible to account for hair follicle initiation in the hair-bearing regions of the mammalian skin as well as the sequence of events required for the formation of dermatoglyphics in the volar regions.

Dermatologists and skin biologists have traditionally approached the diagnosis of skin diseases by either a very gross measurement of its physical state, i.e. a skin pinch, or at the other extreme by being concerned with the cellular and sub-cellular organisation of the skin. Recently, using methods often borrowed from materials science, techniques have been developed and used to aid the investigation of the changes that occur with disease and ageing, for example. A review of these methods developed to study the structure and function of skin by the physical scientists working in close collaboration with dermatologists, pathologists and skin biologists is presented.