Sunscreens - another endangered species?

Skin cancer continues to increase in incidence year-on-year and represents the most common form of cancer across the globe. Every human undergoes premature ageing, particularly on the face, neck and hands. Both phenomena are driven primarily by chronic, daily exposure to solar ultraviolet radiation (UVR). While sunscreen products play a primary role in the prevention of UVR skin damage, the active ingredients, i.e., UVR filters, are facing unprecedented challenges in the coming 10 years and their future is by no means certain. This article, therefore, reviews afresh the facts around photoprotection and the role of sunscreen products in the prevention of acute (sunburn) and chronic (cancer, photoageing) skin damage and compares/contrasts these with various emerging questions and opinions around UVR filter technology. We present a passionate defence of this remarkable technology, but also attempt to imagine a world without it.

L'incidence du cancer de la peau continue d'augmenter année après année, et ce cancer est le plus fréquent dans le monde. Tous les êtres humains connaissent un vieillissement prématuré, en particulier au niveau du visage, du cou et des mains. Les deux phénomènes sont causés principalement par une exposition quotidienne chronique aux rayons ultraviolets (UVR) du soleil. Bien que les protections solaires jouent un rôle essentiel dans la prévention des lésions cutanées dues aux UVR, les principes actifs, c'est-à-dire les filtres UVR, seront confrontés à des difficultés sans précédent dans les 10 prochaines années, et leur avenir n'est en aucun cas certain. Cet article examine donc les faits concernant la photoprotection et le rôle des produits de protection solaire dans la prévention des lésions cutanées aiguës (coups de soleil) et chroniques (cancer, photovieillissement) ; et les compare/oppose aux différentes questions et opinions émergentes concernant la technologie des filtres UVR. Nous présentons une défense passionnée de cette technologie remarquable, mais nous essayons également d'imaginer un monde sans elle.

A New Model to Simulate Human Facial Appearance, Accurately, and Realistically, across Age and Ethnicity.

BACKGROUND: The human population is aging globally, and there is significant, growing interest in modeling and simulating facial appearance. METHODS: The authors describe a new means to model and simulate aging in facial images, using an approach based entirely on 3D whole-face data collected from 1250 female subjects, across 5 ethnicities, ages 10-80. RESULTS: Three models were built, each describing changes with age within each ethnic group, namely shape, color, and topography. These three models were used to build a simulation able to age or de-age a 2D image of a female subject's face, with a degree of accuracy and realism not achievable with previous approaches. Simulated images were validated by a cloud-based age estimator. CONCLUSIONS: The authors have developed a new facial age simulation model, where the use of three submodels (shape, color and topography), built from acquired 3D data, provides both scientifically robust and realistic output. As the data were acquired across five of the world's major ethnicities, this new model allows valuable insight into changes in the facial appearance of our aging global population.

Visual Perception of British Women's Skin Color Distribution in Two Nonindustrialized Societies, the Maasai and the Tsimane'.

In women with lightly pigmented skin in particular, facial skin color homogeneity decreases with age, primarily due to chronic exposure to solar ultraviolet radiation (UVR), leading to a decrease in perceived health and attractiveness. Perception of female skin may be influenced by continuous exposure to, and thus familiarity with, age-related changes in visible skin condition in a given society. Men and women of two traditional societies, the Maasai (Tanzania) and the Tsimane' (Bolivia), unfamiliar with lighter colored skin, judged images of British women's facial skin for age, health, and attractiveness. In both samples, images with homogeneous skin color (from the cheeks of younger women) were judged to be younger and healthier and received a stronger preference than corresponding images with heterogeneous skin color (from older women). We suggest that (i) human sensitivity for quality-related information from facial skin color distribution is universal and independent of any known age-dependent variation in skin in a given population and (ii) skin discoloration is universally associated with less positive judgment.

Topical delivery of hexamidine.

Hexamidine diisethionate (HEX D) has been used for its biocidal actions in topical preparations since the 1950s. Recent data also suggest that it plays a beneficial role in skin homeostasis. To date, the extent to which this compound penetrates the epidermis has not been reported nor how its topical delivery may be modulated. In the present work we set out to characterise the interaction of HEX D with the skin and to develop a range of simple formulations for topical targeting of the active. A further objective was to compare the skin penetration of HEX D with its corresponding dihydrochloride salt (HEX H) as the latter has more favourable physicochemical properties for skin uptake. Candidate vehicles were evaluated by in vitro Franz cell permeation studies using porcine skin. Initially, neat solvents were investigated and subsequently binary systems were examined. The solvents and chemical penetration enhancers investigated included glycerol, dimethyl isosorbide (DMI), isopropyl alcohol (IPA), 1,2-pentanol (1,2-PENT), polyethylene glycol (PEG) 200, propylene glycol (PG), propylene glycol monolaurate (PGML) and Transcutol(®)P (TC). Of a total of 30 binary solvent systems evaluated only 10 delivered higher amounts of active into the skin compared with the neat solvents. In terms of topical efficacy, formulations containing PGML far surpassed all other solvents or binary combinations. More than 70% of HEX H was extracted from the skin following application in PG:PGML (50:50). Interestingly, the same vehicle effectively promoted skin penetration of HEX D but demonstrated significantly lower uptake into and through the skin (30%). The findings confirm the unpredictable nature of excipients on delivery of actives with reference to skin even where there are minor differences in molecular structures. We also believe that they underline the ongoing necessity for fundamental studies on the interaction of topical excipients with the skin.

Preparation and characterisation of hexamidine salts.

Hexamidine diisethionate (HEX D) has been used in the personal care industry and in a number of over-the-counter (OTC) drug products as an antimicrobial agent since the 1950's. Recently, the compound has also been investigated for its beneficial effects on skin health. Surprisingly, there is only limited information describing the physicochemical properties of this compound in the literature. The objective of this work was therefore to conduct a comprehensive programme of characterisation of HEX D as well as its dihydrochloride salt (HEX H). HEX H was prepared from HEX D by a simple acid addition reaction. Both salts were characterised using Nuclear Magnetic Resonance (NMR), Differential scanning calorimetry (DSC), and Thermogravimetric analysis (TGA). A new high performance liquid chromatographic method was developed and validated for both compounds. The pH in aqueous solution as well as respective distribution coefficients between octanol and pH 7.4 buffer were also determined. Finally, solubility and short term stability studies were conducted in a range of solvents. NMR analysis confirmed the preparation of HEX H from HEX D. Thermal analysis indicated the melting points of HEX D and HEX H were 225°C and 266°C respectively. HPLC analysis confirmed the purity of both salts. LogD values at pH 7.4 were -0.74 for HEX D and -0.70 for HEX H respectively. The physicochemical properties of two HEX salts have been established using a range of analytical approaches. Detailed solubility and stability data have also been collated. This information will be useful in the design of novel formulations for targeted delivery of these compounds to the skin.

Determination of the Action Spectrum of UVR-Induced Mitochondrial DNA Damage in Human Skin Cells.

Biological responses of human skin to UVR including cancer and aging are largely wavelength-dependent, as shown by the action spectra of UVR-induced erythema and nuclear DNA (nDNA) damage. A molecular dosimeter of UVR exposure is therefore required. Although mitochondrial DNA (mtDNA) damage has been shown to be a reliable and sensitive biomarker of UVR exposure in human skin, its wavelength dependency is unknown. The current study solves this problem by determining the action spectrum of UVR-induced mtDNA damage in human skin. Human neonatal dermal fibroblasts and primary human adult keratinocyte cells were irradiated with increasing doses of UVR. Dose-response curves of mtDNA damage were produced for each of the UVR sources and cell types, and an action spectrum for each cell type was determined by mathematical induction. Similarities between these mtDNA damage action spectra and previously determined nDNA damage were observed, with the most detrimental effects occurring over the shorter UVR wavelengths. Notably, a statistically significant (P<0.0001) greater sensitivity to mtDNA damage was observed in dermal fibroblasts compared with keratinocytes at wavelengths >300 nm, possibly indicating a wider picture of depth dependence in sensitivity. This finding has implications for disease/photodamage mechanisms and interventions.

A seminar on gardens for the health of the skin.

This is a report on a seminar held on January 12, 2013, at the Regional Dermatology Training Centre in Tanzania, sponsored by the International Society of Dermatology as part of its Taskforce Program for Skin Care for All: Community Dermatology. There were four themes: (i) Gardens attached to health centers increase their attractiveness and result in increased attendance and, thus, increase the utilization of effective skin care interventions. Literature on the positive effect of greenery surrounding health centers on health and the environment is reviewed. (ii) Adding an expert on agriculture to the staff of health centers in Rwanda has provided nutrition and safe medicines. (iii) In southern India, these interventions are channeled through the empowerment of tribal women in an area noted for anxiety due to unemployment in the tea and forestry industry. The gardens are used for teaching about nutrition and herbal medicines, and the women are further attracted by childcare facilities. (iv) Measuring barrier function defects gives early warning of malnutrition of the skin after damage by trauma or by ultraviolet radiation. Higher cost research techniques may help to provide the science required to produce its evidence base. In conclusion, Gardens for health should be adopted as policy by skin care providers.

Self-assembly of palmitoyl lipopeptides used in skin care products.

The self-assembly of three cosmetically active peptide amphiphiles C16-GHK, C16-KT, and C16-KTTKS (C16 denotes a hexadecyl, palmitoyl chain) used in commercial skin care products is examined. A range of spectroscopic, microscopic, and X-ray scattering methods is used to probe the secondary structure, aggregate morphology, and the nanostructure. Peptide amphiphile (PA) C16-KTTKS forms flat tapes and extended fibrillar structures with high ß-sheet content. In contrast, C16-KT and C16-GHK exhibit crystal-like aggregates with, in the case of the latter PA, lower ß-sheet content. All three PA samples show spacings from bilayer structures in small-angle X-ray scattering profiles, and all three have similar critical aggregation concentrations, this being governed by the lipid chain length. However, only C16-KTTKS is stained by Congo red, a diagnostic dye used to detect amyloid formation, and this PA also shows a highly aligned cross-ß X-ray diffraction pattern consistent with the high ß-sheet content in the self-assembled aggregates. These findings may provide important insights relevant to the role of self-assembled aggregates on the reported collagen-stimulating properties of these PAs.

Visual attention to and perception of undamaged and damaged versions of natural and colored female hair.

Female hair color is thought to influence physical attractiveness, and although there is some evidence for this assertion, research has yet not addressed the question if and how physical damaging affects the perception of female hair color. Here we investigate whether people are sensitive (in terms of visual attention and age, health and attractiveness perception) to subtle differences in hair images of natural and colored hair before and after physical damaging. We tracked the eye-gaze of 50 men and 50 women aged 31-50 years whilst they viewed randomized pairs of images of 20 natural and 20 colored hair tresses, each pair displaying the same tress before and after controlled cuticle damage. The hair images were then rated for perceived health, attractiveness, and age. Undamaged versions of natural and colored hair were perceived as significantly younger, healthier, and more attractive than corresponding damaged versions. Visual attention to images of undamaged colored hair was significantly higher compared with their damaged counterparts, while in natural hair, the opposite pattern was found. We argue that the divergence in visual attention to undamaged colored female hair and damaged natural female hair and associated ratings is due to differences in social perception and discuss the source of apparent visual difference between undamaged and damaged hair.

Variation of stratum corneum biophysical and molecular properties with anatomic site.

Several serine protease enzymes are known to be involved in both normal desquamation and the inflammatory processes of the skin. Alteration in the activity of these proteases should also affect corneocyte maturity and size as well as stratum corneum thickness. The aim of the present work was to characterise the baseline changes in corneocyte size, corneocyte maturity, selected protease activity (specifically, Kallikreins-5 and 7, tryptase), protein content and trans-epidermal water loss (TEWL) as a function of anatomic site. The anatomic sites investigated were: cheek, abdomen, wrist and mid-ventral forearm. TEWL values were highest for the cheek (p < 0.05). The TEWL values were also significantly higher (p < 0.05) for cheek and wrist compared with other sites. Protein content was significantly lower for wrist (p < 0.05) compared with other sites. Corneocyte maturity and surface area were significantly (p < 0.05) lower for cheek and wrist compared with other sites. An excellent correlation (r (2) = 0.99) was obtained for maturity and surface area measurements. Kallikrein-5 and tryptase activity were significantly higher for the cheek compared with other sites but Kallikrein-7 values were uniform across sites. The findings have significant implications for skin permeability to drugs and other substances such as environmental toxins depending on the anatomic site of delivery or exposure.

Visible changes of female facial skin surface topography in relation to age and attractiveness perception.

OBJECTIVES: Evolutionary psychology suggests that a woman's age and physical appearance are important mate choice criteria. Given that changes in female facial skin surface topography are important, prominent visible signs of aging, male perceptual sensitivity for variation in this trait may also affect preference and attractiveness judgment. METHODS: Two experiments were conducted to investigate perception (Experiment 1) and noticeability (Experiment 2) of skin surface topography manipulations in facial images of six British women, aged 45-65 years. In Experiment 1 skin surface topography cues were completely removed on the cheeks, the "crow's feet" area adjacent to the eye, under the eyes, above the upper lip, and on the forehead while, in Experiment 2, it was removed gradually (20% increments) on the forehead and around the eyes. In both experiments, stimuli were presented to American and German participants (total N = 300, aged 15-55 years) in omnibus pair-wise combinations (within-face). With each pair, respondents were asked to select that face which they considered as younger looking (Experiments 1 and 2) and more attractive (Experiment 1). RESULTS: Faces with skin surface topography cues removed were judged significantly younger and more attractive than their original (unmodified) counterparts, with modifications on the forehead and around the eyes showing the highest differences. In these areas, participants were able to detect at least a 20% visual change in skin surface topography. CONCLUSIONS: The results support the assertion that even small changes in skin surface topography affect the perceptions of a woman's facial age and attractiveness and may, thus, also influence men's mate preferences.

Chronic sun damage and the perception of age, health and attractiveness.

Young and healthy-looking skin is a feature that is universally admired and considered attractive among humans. However, as we age, skin condition deteriorates due to a variety of intrinsic and extrinsic factors determined not only by genetics and physiological health but also by behaviour and lifestyle choice. As regards the latter, cumulative, repeated exposure to solar ultraviolet radiation (UVR) is linked intrinsically to the induction of specific types of skin cancer and the expression of cutaneous damage markers responsible for the majority of the visible signs of skin ageing. Here we review empirical evidence for skin-specific effects of chronic UVR exposure and relate it to perception of visible skin condition. In contrast to other dermatological accounts, we stress an evolutionary psychology context in understanding the significance of age-related changes in visible skin condition in human social cognition and interaction. We suggest that the "marriage" of the scientific fields of skin biology and evolutionary psychology provides a modern, powerful framework for investigating the causes, mechanisms and perception of chronic sun damage of skin, as it explains the human obsession with a youthful and healthy appearance. Hence, it may be that these insights bring true emotional impetus to the adoption of sun protection strategies, which could conceivably impact skin cancer rates in coming years.

Visual attention to variation in female facial skin color distribution.

OBJECTIVES: Visible skin condition of women is argued to influence human physical attraction. Recent research has shown that people are sensitive to variation in skin color distribution, and such variation affects visual perception of female facial attractiveness, healthiness, and age. METHODS: The eye gaze of 39 males and females, aged 13 to 45 years, was tracked while they viewed images of shape- and topography-standardized stimulus faces that varied only in terms of skin color distribution. RESULTS: The number of fixations and dwell time were significantly higher when viewing stimulus faces with the homogeneous skin color distribution of young people, compared with those of more elderly people. In accordance with recent research, facial stimuli with even skin tones were also judged to be younger and received higher attractiveness ratings. Finally, visual attention measures were negatively correlated with perceived age, but positively associated with attractiveness judgments. CONCLUSIONS: Variation in visible skin color distribution (independent of facial form and skin surface topography) is able to selectively attract people's attention toward female faces, and this higher attention results in more positive statements about a woman's face.

New insights into skin appearance and measurement.

When viewing the human face, the eye is drawn automatically to the areas of uneven topography and high color contrast, and the perception of skin age and attractiveness is dependent on these features. Although it is well recognized that topographic features, such as lines and wrinkles, contribute to the perceived age of skin and many cosmetic procedures are directed toward modifying these, the contribution of color contrast to the perceived age of skin has been less widely studied. A new technique, spectrophotometric intracutaneous analysis, is able to measure and characterize the distribution of chromophores in aging human skin and represents a significant advance in evaluation of the role color contrast plays in perception of the aging human face. This technique may be useful in the assessment of cosmetic interventions to reduce the appearance of aging by modification of skin color.

Color homogeneity and visual perception of age, health, and attractiveness of female facial skin.

BACKGROUND: Evolutionary psychology suggests that skin signals aspects of mate value, yet only limited empirical evidence exists for this assertion. OBJECTIVES: We sought to study the relationship between perception of skin condition and homogeneity of color/chromophore distribution. METHODS: Cropped skin cheek images from 170 girls and women (11-76 years) were blind-rated for attractiveness, healthiness, youthfulness, and biological age by 353 participants. These skin images and corresponding melanin/hemoglobin concentration maps were analyzed objectively for homogeneity. RESULTS: Homogeneity of unprocessed images correlated positively with perceived attractiveness, healthiness, and youthfulness (all r > 0.40; P < .001), but negatively with estimated age (r = -0.45; P < .001). Homogeneity of hemoglobin and melanin maps was positively correlated with that of unprocessed images (r = 0.92, 0.68; P < .001) and negatively correlated with estimated age (r = -0.32, -0.38; P < .001). LIMITATIONS: Female skin only was studied. CONCLUSIONS: Skin color homogeneity, driven by melanin and hemoglobin distribution, influences perception of age, attractiveness, health, and youth.

Solar ultraviolet radiation: definitions and terminology.

In the rapidly developing field of photobiology as it relates to solar ultraviolet radiation (UVR), there is a need as never before to ensure that definitions and terminology are current, correct, and standard. This article provides a basic definition of UVR; a review of correct UVR radiometric symbols, units, and nomenclature; defines extraterrestrial and terrestrial solar UVR; and reviews the measurement of biologically effective dose of solar UVR in humans.

Ultraviolet A radiation: testing and labeling for sunscreen products.

Conceptually, sunscreen products are quite simple. The ultraviolet (UV) filters in these products reduce the "dose" of solar energy to which the skin is exposed. Underlying this empirical notion are many complexities including measures of product efficacy and how to communicate this to consumers. The sun protection factor (SPF) test is and should remain the singular in vivo method for evaluating sunscreens. Additionally, substrate spectrophotometric measure of absorbance/transmittance and the calculation of the summary statistic, such as the critical wavelength (ie, lambda(c)), should be used as a means of evaluating broad-spectrum (ie, UVA) protection. Ideally, the photoprotective efficacy of sunscreen products will be communicated to consumers as an SPF no greater than 50 and a single designation of "broad-spectrum" to indicate long-wavelength UVA protection.