Sunscreen penetration of human skin and related keratinocyte toxicity after topical application

Sunscreen skin penetration and safety assessment should be considered together in order to ensure that in vitro cytotoxicity studies examine relevant doses of these organic chemical UV filters to which viable epidermal cells are realistically exposed. In this study, we sought to determine whether sufficient topically applied sunscreens penetrated into human viable epidermis to put the local keratinocyte cell populations at risk of toxicity. The penetration and retention of five commonly used sunscreen agents ( avobenzone, octinoxate, octocrylene, oxybenzone and padimate O) in human skin was evaluated after application in mineral oil to isolated human epidermal membranes. Sunscreen concentration - human keratinocyte culture response curves were then defined using changes in cell morphology and proliferation ( DNA synthesis using radiolabelled thymidine uptake studies) as evidence of sunscreens causing toxicity. Following 24 h of human epidermal exposure to sunscreens, detectable amounts of all sunscreens were present in the stratum corneum and viable epidermis, with epidermal penetration most evident with oxybenzone. The concentrations of each sunscreen found in human viable epidermis after topical application, adjusting for skin partitioning and binding effects, were at least 5-fold lower, based on levels detected in viable epidermal cells, than those appearing to cause toxicity in cultured human keratinocytes. It is concluded that the human viable epidermal levels of sunscreens are too low to cause any significant toxicity to the underlying human keratinocytes. Copyright (C) 2005 S. Karger AG, Basel.

Long-term increase in sunscreen use in an Australian community after a skin cancer prevention trial

Background. Given the public health burden of skin cancer in white populations, an increase in sun protective behavior is needed. In a highrisk community, we assessed long-term Sunscreen use among people who had participated in a randomized trial of daily Sunscreen application for prevention of skin cancer. Methods. In 1992, 1621 residents of the subtropical Australian township of Nambour were randomly allocated to either daily or discretionary sunscreen use until 1996. From 1997 to 2002, we monitored by questionnaires their ongoing sunscreen use. Results. People who had never or irregularly used sunscreen when in summer sun before the trial were more likely (P < 0.0001) to be sustaining regular application especially to their face (20% vs. 11%) and forearms (14% vs. 5%) if they had been allocated to daily, not discretionary, use of sunscreen for 5 years. Conclusions. Regular voluntary sunscreen use for skin cancer prevention can be sustained by sun-sensitive people in the long term. Habit formation appears to be an important goal for sun protection programs among those living, or on vacation, in sunny places. (c) 2005 Elsevier Inc. All rights reserved.

Prolonged prevention of squamous cell carcinoma of the skin by regular sunscreen use

Half of all cancers in the United States are skin cancers. We have previously shown in a 4.5-year randomized controlled trial in an Australian community that squamous cell carcinomas (SCC) but not basal cell carcinomas (BCC) can be prevented by regular sunscreen application to the head, neck, hands, and forearms. Since cessation of the trial, we have followed participants for a further 8 years to evaluate possible latency of preventive effect on BCCs and SCCs. After prolonged follow-up, BCC tumor rates tended to decrease but not significantly in people formerly randomized to daily sunscreen use compared with those not applying sunscreen daily. By contrast, corresponding SCC tumor rates were significantly decreased by almost 40% during the entire follow-up period (rate ratio, 0.62; 95% confidence interval, 0.38-0.99). Regular application of sunscreen has prolonged preventive effects on SCC but with no clear benefit in reducing BCC.

Expression of p53 tumor suppressor protein in sun-exposed skin and associations with sunscreen use and time spent outdoors: A community-based study

The p53 gene is a tumor suppressor gene that is commonly mutated in skin cancer and sun-exposed skin, and this can be detected through immunohistochemical expression of the p53 protein. The authors hypothesized that time spent outdoors is associated with p53 protein expression in human skin and that sunscreen use counteracts the association. In 1996, they investigated this in a community-based cross-sectional study in Australia. Detailed information about skin type, time spent outdoors, and sunscreen use was collected from 139 residents of a subtropical township who also provided a skin biopsy from the back of the hand for measurement of p53 expression. Increasing time spent outdoors was positively associated with immuno reactivity in the whole epidermis and in the basal layer of the epidermis. After adjustment for confounders, p53 immunoreactivity was twice as high for people who used sunscreen 1 or 2 days per week as for those who used sunscreen daily (whole epidermis: ratio estimate = 2.0, 95% confidence interval: 1.1, 3.6; basal layer: ratio estimate = 1.7, 95% confidence interval: 0.9, 3.1). The authors conclude that p53 immunoreactivity in the skin is a marker of exposure to ultraviolet light in the past 6 months, but this may be mitigated by regular application of sunscreen.

Daily sunscreen application and betacarotene supplementation in prevention of basal-cell and squamous-cell carcinomas of the skin: a randomised controlled trial

Background The use of sunscreens on the skin can prevent sunburn but whether long-term use can prevent skin cancer is not known. Also, there is evidence that oral betacarotene supplementation lowers skin-cancer rates in animals, but there is limited evidence of its effect in human beings. Methods In a community-based randomised trial with a 2 by 2 factorial design, individuals were assigned to four treatment groups: daily application of a sun protection factor 15-plus sunscreen to the head, neck, arms, and hands, and betacarotene supplementation (30 mg per day); sunscreen plus placebo tablets; betacarotene only; or placebo only. Participants were 1621 residents of Nambour in southeast Queensland, Australia. The endpoints after 4.5 years of follow-up were the incidence of basal-cell and squamous-cell carcinomas both in terms of people treated for newly diagnosed disease and in terms of the numbers of tumours that occurred. Analysis of the effect of sunscreen was based only on skin cancers that developed on sites of daily application. All analyses were by intention to treat. Findings 1383 participants underwent full shin examination by a dermatologist in the follow-up period. 250 of them developed 758 new skin cancers during the follow-up period. There were no significant differences in the incidence of first new shin cancers between groups randomly assigned daily sunscreen and no daily sunscreen (basal-cell carcinoma 2588 vs 2509 per 100 000; rate ratio 1.03 [95% CI 0.73-1.46]; squamous-cell carcinoma 876 vs 996 per 100 000; rate ratio 0.88 [0.50-1.56]). Similarly, there was no significant difference between the betacarotene and placebo groups in incidence of either cancer (basal-cell carcinoma 3954 vs 3806 per 100 000; 1.04 [0.73-1.27]; squamous-cell carcinoma 1508 vs 1146 per 100 000; 1.35 [0.84-2.19]). In terms of the number of tumours, there was no effect on incidence of basal-cell carcinoma by sunscreen use or by betacarotene but the incidence of squamous-cell carcinoma was significantly lower in the sunscreen group than in the no daily sunscreen group (1115 vs 1832 per 100 000; 0.61 [0.46-0.81]). Interpretation There was no harmful effect of daily use of sunscreen in this medium-term study. Cutaneous squamous-cell carcinoma, but not basal-cell carcinoma seems to be amenable to prevention through the routine use of sunscreen by adults for 4.5 years. There was no beneficial or harmful effect on the rates of either type of skin cancer, as a result of betacarotene supplementation.

Toxicity assessment of industrial- and sunscreen-derived ZnO nanoparticles

Lo scopo della presente tesi è l’analisi della tossicità di nanoparticelle di ossido di zinco (nano-ZnO) verso gli organismi acquatici. In particolare, il presente studio valuta per la prima volta l'inibizione della crescita della diatomea Thalassiosira pseudonana indotta sia da nanoparticelle di dervazione industriale, che da nanoparticelle auto-estratte in laboratorio da un filtro solare. Gli esperimenti, condotti presso il Laboratorio di Ingegneria dell'Università di Miami, hanno mostrato che la tossicità indotta dalle nanoparticelle di ossido di zinco è influenzata dal tipo di nanoparticelle, nonché dalla loro concentrazione nella soluzione acquosa e dal tempo di esposizione. In particolare le nanoparticelle di derivazione industriale, più piccole rispetto alle nanoparticelle estratte dal filtro solare, hanno indotto un’inibizione della crescita superiore, specialmente a concentrazioni inferiori. Questo andamento suggerisce che ad alte concentrazioni la tossicità di nano-ZnO potrebbe essere influenzata dall’aggregazione di nanoparticelle (indipendentemente dalle dimensioni di partenza delle nanoparticelle), mentre a concentrazioni inferiori la tossicità potrebbe essere influenzata dalle dimensioni di partenza delle nanoparticelle, così come dal tipo di nanoparticelle e dal tempo di esposizione.

In Vitro Evaluation Of Sun Protection Factor And Stability Of Commercial Sunscreens Using Mass Spectrometry.

Sunlight exposure causes several types of injury to humans, especially on the skin; among the most common harmful effects due to ultraviolet (UV) exposure are erythema, pigmentation and lesions in DNA, which may lead to cancer. These long-term effects are minimized with the use of sunscreens, a class of cosmetic products that contains UV filters as the main component in the formulation; such molecules can absorb, reflect or diffuse UV rays, and can be used alone or as a combination to broaden the protection on different wavelengths. Currently, worldwide regulatory agencies define which ingredients and what quantities must be used in each country, and enforce companies to conduct tests that confirm the Sun Protection Factor (SPF) and the UVA (Ultraviolet A) factor. Standard SPF determination tests are currently conducted in vivo, using human subjects. In an industrial mindset, apart from economic and ethical reasons, the introduction of an in vitro method emerges as an interesting alternative by reducing risks associated to UV exposure on tests, as well as providing assertive analytical results. The present work aims to describe a novel methodology for SPF determination directly from sunscreen formulations using the previously described cosmetomics platform and mass spectrometry as the analytical methods of choice.

In Vivo Xylitol Primary Dermal Irritation and Phototoxicity Evaluation

Xylitol is a widely studied sugar with therapeutic properties and is effective against microorganisms. Despite a variety of toxicological data being available about this compound, dermal toxicological tests cannot be found. Here, the aim was to carry out in vivo assays to verify xylitol skin application safety. Primary dermal irritation studies were done with rabbits using 5 and 10% (w/w) xylitol, in either cream or gel form. Phototoxicity assays were also performed with guinea pigs, using only 10% (w/w) xylitol, in both forms. Primary dermal irritation studies revealed that xylitol topically used (5 and 10%) did not induce erythema or edema formation, but did show phototoxicity properties. Xylitol is an adequate alternative compound to be applied for skin disease control, since this application will be done together with sunscreen.

In Vitro Sun Protection Factor Evaluation of Sunscreens Containing Rutin and its Derivative

This research aimed at determining spectrophotometrically (290 to 320nm) the in vitro Sun Protection Factor (SPF) of sunscreens developed with rutin (R) or succinate rutin (SR), in association or not with UVB filter. Formulations were developed based on phosphate-base O/W emulsions, with (B) or not (A) the presence of polyacrylamide/C13-14 isoparaffin/laureth-7 (PIL), in accordance with the following associations: (a) control; (b) 1.0 % SR; (c) 0.1 % R; (d) 7.5 % ethylhexyl methoxycinnamate (EHMC); (e) 7.5 % EHMC + 0.1 % RS; (0 7.5 % EHMC + 0.1 % R. It was verified a statistical significative elevation of the SPF from 13.93 +/- 0.02 (Af) to 16.63 +/- 0.27 (Bf) and also in relation to 15.53 +/- 0.14 (Bd). According to the results, the EHMC had distinct behavior depending on the presence of bioactive substance and viscosity agent, thus, rutin obtained better profile as a SPF booster in these experimental conditions with the presence of PIL.

Broad spectrum bioactive sunscreens

The development of sunscreens containing reduced concentration of chemical UV filters, even though, possessing broad spectrum effectiveness with the use of natural raw materials that improve and infer UV absorption is of great interest. Due to the structural similarities between polyphenolic compounds and organic UV filters, they might exert photoprotection activity. The objective of the present research work was to develop bioactive sunscreen delivery systems containing rutin, Passiflora incarnata L. and Plantago lanceolata extracts associated or not with organic and inorganic UV filters. UV transmission of the sunscreen delivery system films was performed by using diffuse transmittance measurements coupling to an integrating sphere. In vitro photoprotection efficacy was evaluated according to the following parameters: estimated sun protection factor (SPF); Boot`s Star Rating category; UVA/UVB ratio; and critical wavelength (lambda(c)). Sunscreen delivery systems obtained SPF values ranging from 0.972 +/- 0.004 to 28.064 +/- 2.429 and bioactive compounds interacted with the UV filters positive and negatively. This behavior may be attributed to: the composition of the delivery system: the presence of inorganic UV filter and quantitative composition of the organic UV filters; and the phytochemical composition of the P. incarnate L and P. lanceolato extracts. Among all associations of bioactive compounds and UV filters, we found that the broad spectrum sunscreen was accomplished when 1.68% (w/w) P incarnata L. dry extract was in the presence of 7.0% (w/w) ethylhexyl methoxycinnamate, 2.0% (w/w) benzophenone-3 and 2.0% (w/w) TiO(2). It was demonstrated that this association generated estimated SPF of 20.072 +/- 0.906 and it has improved the protective defense against UVA radiation accompanying augmentation of the UVA/UVB ratio from 0.49 to 0.52 and lambda(c) from 364 to 368.6 nm. (c) 2008 Elsevier B.V. All rights reserved.

In Vivo Evaluation of the Photoprotective Efficacy of O-1/W/O-2 Multiple Emulsions with Andiroba Oil (Carapa guianensis)

Stable multiple emulsions containing andiroba oil and sunscreen have been formulated. These were prepared using the two-step procedure. The formulations were characterized and their stability over the time was evaluated by centrifugation, macroscopic, and microscopic analyses, and rheological measurements. The photoprotective efficacy of the O/W and O1/W/O2 containing or not andiroba oil was evaluated by in vivo sun protection factor determination according to the FDA method. The formulations exhibited good stability during 30 days after preparation at different temperatures. These presented pseudoplastic flow behaviour and thixotropy. The increase of in vivo SPF value was not observed when andiroba oil was incorporated into emulsions containing ethylhexyl methoxycinnamate. These multiple emulsions can be utilized as an interesting topical vehicle.

Influence of the Photostabilizer in the Photoprotective Effects of a Formulation Containing UV-Filters and Vitamin A

Vitamin A palmitate has been used in cosmetics; however, studies report that this substance shows photoreactivity that can lead to loss of safety and efficacy. On the other hand, photostabilizers have been used to increase sunscreen photostability and consequently their safety and effectiveness. Thus, this study aimed to evaluate the influence of photostabilizers on the photoprotective effects of a cosmetic formulation containing UV-filters and vitamin A palmitate. The formulation containing UV-filters was supplemented with vitamin A palmitate and the photostabilizers diethylhexyl 2,6-naphthalate (DEHN), bumetrizole and benzotriazolyl dodecyl p-cresol (BTDC). Hairless mice were treated daily by topical applications and irradiated (UVA/B). Erythema index, transepidermal water loss, histological/histometric analysis and number of sunburn cells (SBC) were evaluated. The results showed that all formulations protected from UV-induced enhancement of erythema and SBC but there was no difference among them. The formulation with no stabilizers reduced viable epidermis thickness due to atrophy induced by UV radiation. Thus, it can be concluded that the presence of photostabilizers influenced the effects of formulations containing UV-filters and vitamin A palmitate, which could be seen by histological and histometric analysis. Furthermore, the formulations containing the stabilizers DEHN and BTDC showed better protective effects on hairless mice skin.

A HPLC method to evaluate the influence of photostabilizers on cosmetic formulations containing UV-filters and vitamins A and E

This paper reports a simple and reliable HPLC method to evaluate the influence of two currently available photostabilizers on cosmetic formulations containing combined UV-filters and vitamins A and E. Vitamins and UV-filters, widely encountered in products of daily use have to be routinely evaluated since photoinstability can lead to reductions in their efficacy and safety. UV-irradiated formulation samples were submitted to a procedure that included a reliable, precise and specific HPLC method employing a C18 column and detection at 325 and 235 nm. Methanol, isopropanol and water were the mobile phases in gradient elution. The method precision was between 0.28 and 5.07. The photostabilizers studied [diethylhexyl 2,6-naphthalate (DEHN) and benzotriazolyl dodecyl p-cresol (BTDC)], influenced the stability of octyl methoxycinnamate (OMC) associated with vitamins A and E. BTDC was considered the best photostabilizer to vitamins and OMC when the UV-filters were combined with both vitamins A and E. (C) 2010 Elsevier B.V. All rights reserved.

Absorption of sunscreens across human skin: an evaluation of commercial products for children and adults

Aims Topical sunscreens are routinely applied to the skin by a large percentage of the population. This study assessed the extent of absorption of a number of common chemical sunscreen agents into and through human skin following application of commercially available products. Methods Sunscreen products were applied to excised human epidermis in Franz diffusion cells with the amount penetrating into and across the epidermis assessed by h.p.l.c. for 8 h following application. Results All sunscreen agents investigated penetrated into the skin (0.25 g m(-2) or 14% of applied dose), but only benzophenone-3 passed through the skin in significant amounts (0.08 g m(-2) or 10% of the applied dose). With one exception, suncreen agents in corresponding products marketed for adults and children had similar skin penetration profiles. Conclusions Whilst limited absorption across the skin was observed for the majority of the sunscreens tested, benzophenone-3 demonstrated sufficiently high penetration to warrant further investigation of its continued application.

Melanoma in adolescents: A case-control study of risk factors in Queensland, Australia

The incidence of melanoma increases markedly in the second decade of life but almost nothing is known of the causes of melanoma in this age group. We report on the first population-based case-control study of risk factors for melanoma in adolescents (15-19 years). Data were collected through personal interviews with cases, controls and parents. A single examiner conducted full-body nevus counts and blood samples were collected from cases for analysis of the CDKN2A melanoma predisposition gene. A total of 201 (80%) of the 250 adolescents with melanoma diagnosed between 1987 and 1994 and registered with the Queensland Cancer Registry and 205 (79%) of 258 age-, gender- and location-matched controls who were contacted agreed to participate. The strongest risk factor associated with melanoma in adolescents in a multivariate model was the presence of more than 100 nevi 2 mm or more in diameter (odds ratio [OR] = 46.5, 95% confidence interval [Cl] = 11.4-190.8). Other risk factors were red hair (OR = 5.4, 95%Cl = 1.0-28.4); blue eyes (OR = 4.5, 95%Cl = 1.5- 13.6); inability to tan after prolonged sun exposure (OR = 4.7, 95%Cl = 0.9-24.6); heavy facial freckling (OR = 3.2, 95% Cl = 0.9-12.3); and family history of melanoma (OR = 4.0, 95%Cl = 0.8-18.9). Only 2 of 147 cases tested had germline variants or mutations in CDKN2A. There was no association with sunscreen use overall, however, never/rare use of sunscreen at home under the age of 5 years was associated with increased risk (OR = 2.2, 95%Cl = 0.7-7.1). There was no difference between cases and controls in cumulative sun exposure in this high-exposure environment. Factors indicating genetic susceptibility to melanoma, in particular, the propensity to develop nevi and freckles, red hair, blue eyes, inability to tan and a family history of the disease are the primary determinants of melanoma among adolescents in this high solar radiation environment. Lack of association with reported sun exposure is consistent with the high genetic susceptibility in this group. (C) 2002 Wiley-Liss, Inc.