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Background: Regular exposure to ultraviolet rays is high in India, where most Indians present Fitzpatrick skin phototypes IV and V. Aims: To evaluate the efficacy and compare the effectiveness of two sunscreen products on Indian skin types IV and V with pigmentation irregularities. Methods: A randomized, uncontrolled and investigator-blinded, single-center study enrolled adult men and women (18-45 years) with Fitzpatrick skin phototypes IV (28° < individual typological angle <10°) and V (10° < individual typological angle < −30°) with pigmentary abnormalities seen on the face in adults (actinic lentigines and postinflammatory hyperpigmentation), who did not use sunscreens. Participants were randomized (1:1) to either of the two marketed sunscreen products, Product A (sun protection factor 50 PA+++) or Product B (sun protection factor 19 PA+++), applied twice daily before sun exposure for ≥2 h. Primary objectives aimed at assessing possible improvement in hyperpigmented spots and overall skin appearance after 12 weeks of use. Evaluation of skin radiance and skin color was done by means of L'Oréal color chart and colorimetric measurements (Chromameter®). Results: Among the 230 enrolled participants, 216 (93.91%) completed the study. The clinical assessment of the density of pigmented spots and skin radiance showed significant (P < 0.001) improvement in both groups during all visits. The qualitative (participant perception) and quantitative (Chromameter®) data indicated improvement in pigmentation from Week 0 to Week 12. Both products were well-tolerated. Limitations: The study was conducted over a rather short period of time (12 weeks) at a single location. Conclusions: This is the first study conducted on Indian skin phototypes IV and V under real-life conditions. It demonstrated the effect of regular sunscreen usage in the prevention of certain signs of skin photoaging such as increased pigmentation or pigmentary abnormalities, thus providing support and assistance to clinicians in suggesting the use of efficient sun-screening products to patients.

Many chameleons, and panther chameleons in particular, have the remarkable ability to exhibit complex and rapid colour changes during social interactions such as male contests or courtship. It is generally interpreted that these changes are due to dispersion/aggregation of pigment-containing organelles within dermal chromatophores. Here, combining microscopy, photometric videography and photonic band-gap modelling, we show that chameleons shift colour through active tuning of a lattice of guanine nanocrystals within a superficial thick layer of dermal iridophores. In addition, we show that a deeper population of iridophores with larger crystals reflects a substantial proportion of sunlight especially in the near-infrared range. The organization of iridophores into two superposed layers constitutes an evolutionary novelty for chameleons, which allows some species to combine efficient camouflage with spectacular display, while potentially providing passive thermal protection. Colour change in many vertebrates originates from pigment dispersion or aggregation. Here, Teyssier et al . show that chameleons rapidly shift colour through a physical mechanism involving a lattice of nanocrystals in dermal iridophores, a second and deeper iridophore layer strongly reflects near-infrared light.

Background: 8-oxoguanine, a major product of DNA oxidation, is considered a key parameter in measuring the carcinogenic effects of ultraviolet radiation. Objective: To assess and compare the carcinogenic potential of different photo (chemo) therapeutic modalities in photoresponsive skin diseases by measuring the levels of 8-oxoguanine in dark-skinned individuals before and after photo (chemo) therapy. Methods: A prospective, randomized controlled pilot study was conducted in 63 patients of skin types III-V with photo-responsive dermatoses including vitiligo, psoriasis and mycosis fungoides. Patients were divided into three groups; Group 1 (received narrowband ultraviolet-B), Group 2 (received psoralen plus ultraviolet-A) and Group 3 (received broadband ultraviolet-A). Biopsies were taken before and after phototherapy to measure 8-oxoguanine levels using enzyme-linked immunosorbent assay. Biopsies were also taken from the sun-protected skin in 21 controls subjects who had no dermatological disease. Results: Regardless of the disease, a significantly higher level of 8-oxoguanine was found after treatment when compared to the pre-treatment baseline levels; however, these levels were comparable to those in control subjects. A weakly significant positive correlation was found between cumulative dose and 8-oxoguanine levels following psoralen plus ultraviolet-A therapy. In controls, comparing the 8-oxoguanine levels between skin types III and IV showed significantly lower 8-oxoguanine in skin type IV. Conclusion: Therapeutic doses of ultraviolet radiation are relatively safe in dark skinned patients; however, minimizing the cumulative dose of phototherapeutic modalities (particularly psoralen plus ultraviolet-A) is recommended.

Many cephalopods escape detection using camouflage 1 . This behaviour relies on a visual assessment of the surroundings, on an interpretation of visual-texture statistics 2 – 4 and on matching these statistics using millions of skin chromatophores that are controlled by motoneurons located in the brain 5 – 7 . Analysis of cuttlefish images proposed that camouflage patterns are low dimensional and categorizable into three pattern classes, built from a small repertoire of components 8 – 11 . Behavioural experiments also indicated that, although camouflage requires vision, its execution does not require feedback 5 , 12 , 13 , suggesting that motion within skin-pattern space is stereotyped and lacks the possibility of correction. Here, using quantitative methods 14 , we studied camouflage in the cuttlefish Sepia officinalis as behavioural motion towards background matching in skin-pattern space. An analysis of hundreds of thousands of images over natural and artificial backgrounds revealed that the space of skin patterns is high-dimensional and that pattern matching is not stereotyped—each search meanders through skin-pattern space, decelerating and accelerating repeatedly before stabilizing. Chromatophores could be grouped into pattern components on the basis of their covariation during camouflaging. These components varied in shapes and sizes, and overlay one another. However, their identities varied even across transitions between identical skin-pattern pairs, indicating flexibility of implementation and absence of stereotypy. Components could also be differentiated by their sensitivity to spatial frequency. Finally, we compared camouflage to blanching, a skin-lightening reaction to threatening stimuli. Pattern motion during blanching was direct and fast, consistent with open-loop motion in low-dimensional pattern space, in contrast to that observed during camouflage. The cuttlefish Sepia officinalis uses high-dimensional skin patterns for camouflage, and the pattern matching process is not stereotyped—each search meanders through skin-pattern space, decelerating and accelerating repeatedly before stabilizing.

Skin pigmentation is a classic example of a polygenic trait that has experienced directional selection in humans. Genome-wide association studies have identified well over a hundred pigmentation-associated loci, and genomic scans in present-day and ancient populations have identified selective sweeps for a small number of light pigmentation-associated alleles in Europeans. It is unclear whether selection has operated on all of the genetic variation associated with skin pigmentation as opposed to just a small number of large-effect variants. Here, we address this question using ancient DNA from 1,158 individuals from West Eurasia covering a period of 40,000 y combined with genome-wide association summary statistics from the UK Biobank. We find a robust signal of directional selection in ancient West Eurasians on 170 skin pigmentation-associated variants ascertained in the UK Biobank. However, we also show that this signal is driven by a limited number of large-effect variants. Consistent with this observation, we find that a polygenic selection test in present-day populations fails to detect selection with the full set of variants. Our data allow us to disentangle the effects of admixture and selection. Most notably, a large-effect variant at SLC24A5 was introduced to Western Europe by migrations of Neolithic farming populations but continued to be under selection post-admixture. This study shows that the response to selection for light skin pigmentation in West Eurasia was driven by a relatively small proportion of the variants that are associated with present-day phenotypic variation.

Skin disorders showing abnormal pigmentation are often difficult to manage because of their uncertain etiology or pathogenesis. Abnormal pigmentation is a common symptom accompanying aging skin. The association between skin aging and skin pigmentation abnormalities can be attributed to certain inherited disorders characterized by premature aging and abnormal pigmentation in the skin and some therapeutic modalities effective for both. Several molecular mechanisms, including oxidative stress, mitochondrial DNA mutations, DNA damage, telomere shortening, hormonal changes, and autophagy impairment, have been identified as involved in skin aging. Although each of these skin aging-related mechanisms are interconnected, this review examined the role of each mechanism in skin hyperpigmentation or hypopigmentation to propose the possible association between skin aging and pigmentation abnormalities.

Skin color patterns are ubiquitous in nature, impact social behavior, predator avoidance, and protection from ultraviolet irradiation. A leading model system for vertebrate skin patterning is the zebrafish; its alternating blue stripes and yellow interstripes depend on light-reflecting cells called iridophores. It was suggested that the zebrafish’s color pattern arises from a single type of iridophore migrating differentially to stripes and interstripes. However, here we find that iridophores do not migrate between stripes and interstripes but instead differentiate and proliferate in-place, based on their micro-environment. RNA-sequencing analysis further reveals that stripe and interstripe iridophores have different transcriptomic states, while cryogenic-scanning-electron-microscopy and micro-X-ray diffraction identify different crystal-arrays architectures, indicating that stripe and interstripe iridophores are different cell types. Based on these results, we present an alternative model of skin patterning in zebrafish in which distinct iridophore crystallotypes containing specialized, physiologically responsive, organelles arise in stripe and interstripe by in-situ differentiation. The skin of zebrafish is patterned by alternating blue stripes and yellow interstripes which arises from guanine crystal-containing cells called iridophores that reflect light. Here the authors track iridophores and see that they do not migrate between stripes and interstripes, but instead differentiate and proliferate in place based on their micro-environment.

Melanocytes are phenotypically prominent but histologically inconspicuous skin cells. They are responsible for the pigmentation of skin and hair, and thereby contribute to the appearance of skin and provide protection from damage by ultraviolet radiation. Pigmentation mutants in various species are highly informative about basic genetic and developmental pathways, and provide important clues to the processes of photoprotection, cancer predisposition and even human evolution. Skin is the most common site of cancer in humans. Continued understanding of melanocyte contributions to skin biology will hopefully provide new opportunities for the prevention and treatment of skin diseases.

Autophagy is a membrane traffic system that provides sustainable degradation of cellular components for homeostasis, and is thus considered to promote health and longevity, though its activity declines with aging. The present findings show deterioration of autophagy in association with premature skin aging. Autophagy flux was successfully determined in skin tissues, which demonstrated significantly decreased autophagy in hyperpigmented skin such as that seen in senile lentigo. Furthermore, an exacerbated decline in autophagy was confirmed in xerotic hyperpigmentation areas, accompanied by severe dehydration and a barrier defect, which showed correlations with skin physiological conditions. The enhancement of autophagy in skin ex vivo ameliorated skin integrity, including pigmentation and epidermal differentiation. The present results indicate that the restoration of autophagy can contribute to improving premature skin aging by various intrinsic and extrinsic factors via the normalization of protein homeostasis.

Melanin in the epidermis determines the wide variation in skin color associated with ethnic skin diversity. Ethnic differences exist regarding melanosome loss in keratinocytes, but the mechanisms underlying these differences, and their contribution to the regulation of skin color, remain unclear. Here, we explored the involvement of autophagy in determining skin color by regulating melanosome degradation in keratinocytes. Keratinocytes derived from Caucasian skin exhibit higher autophagic activity than those derived from African American (AA) skin. Furthermore, along with the higher autophagy activity in Caucasian skin–derived keratinocytes compared with AA skin–derived keratinocytes, Caucasian skin–derived keratinocytes were more sensitive to melanosome treatment as shown by their enhanced autophagic activity, which may reflect the substantial mechanisms in the human epidermis owing to the limitations of the models. Melanosome accumulation in keratinocytes was accelerated by treatment with lysosomal inhibitors or with small interfering RNAs specific for autophagy-related proteins, which are essential for autophagy. Furthermore, consistent with the alterations in skin appearance, the melanin levels in human skin cultured ex vivo and in human skin substitutes in vitro were substantially diminished by activators of autophagy and enhanced by the inhibitors. Taken together, our data reveal that autophagy has a pivotal role in skin color determination by regulating melanosome degradation in keratinocytes, and thereby contributes to the ethnic diversity of skin color.