Study of the photostability of 18 sunscreens in creams by measuring the SPF in vitro

doi:10.1016/j.jpba.2007.01.052

Journal of Pharmaceutical and Biomedical Analysis

Volume 44, Issue 1, 9 May 2007, Pages 270-273

https://doi.org/10.1016/j.jpba.2007.01.052 Get rights and content

Abstract

The target of this research was to evaluate the photostability of various sunscreen agents incorporated into an O/W emulsion. The concept of photostability is very important in the field of solar protection. The effectiveness of the anti-solar products is quantified using a universal indicator: the sun protection factor (SPF). This number which can be found on packaging can be given in two different ways: by methods in vivo (Colipa method) and in vitro. It is this last method which was adopted for this study. According to selected filter UVB (currently directive 76/768/EEC modified authorized 18 filters UVB), we can obtain more or less effective creams. We chose the irradiation of sun lotions formulated using the authorized filters, used with their maximum amount of employment, in a Suntest, with an irradiance of 650 W/m² throughout variable time. With interval of regular time, one carries out a measurement of SPF in order to establish for each filter the kinetics SPF = f(time). An indicator of stability (t₉₀) is then given. In this way, we could classify the filters by order of increasing photostability.

Introduction

It is a well-known fact that an over exposure of human skin to ultraviolet light may lead to sunburn cells, premature skin aging and an increased risk for skin cancers [1], [2], [3], [4]. The steady increase in the incidence of melanoma, non-melanoma cutaneous neoplasia and preneoplasic disorders has contributed to the demand for more effective protection from the sun. Sunscreen products are intended to protect the skin from the deleterious effects of the sun. In order to guarantee constant efficacy of sunscreen products, the UV filters used should be photostable [1], [2], [3]. In this work, we studied the kinetics of photostability of 18 UV filters authorized in European Union [5] by determination of SPF of O/W emulsion containing each sunscreen agent.

Section snippets

Materials

The sunscreens and their characteristics are presented in Table 1. Dimethicone (Abil^® WE 09) was obtained from Goldschmidt (Montigny-le-Bretonneux, France). Cetiol^® HE, stearic acid, glycerin, parabens and triethanolamine (TEA) were purchased from Cooper (Melun, France). Xanthan gum (Keltrol^® BT) was obtained from Kelco (Lille Skensved, Denmark). Polymethylmethacrylate (PMMA) plates were purchased from Helioscience (Creil, France).

Preparation of sunscreen creams

An O/W emulsion was prepared in the laboratory by adding known

Results and discussion

To fulfil the requirements of sunscreen formulation a silicon cream was chosen [10].

The experimental conditions were determined by correlating the results obtained in vitro with the creams manufactured by the authors with the results obtained in vivo with the same creams, using the protocol recommended by the Colipa (the European Cosmetic Toiletry and Perfumery Association) in the SPF range [1–30] [11]. Furthermore, there is no difference of anti-solar efficacy of homosalate 8% into the FDA

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Les produits de protection solaire (PPS) composés de filtres chimiques et/ou de filtres minéraux occupent aujourd’hui une place importante en photoprotection. Ils ont été à l’origine de larges polémiques, dont certaines ne sont pas éteintes, sur leur efficacité réelle en prévention primaire des cancers cutanés (CC), ainsi que sur leurs risques sanitaire et écologique potentiels. Les filtres chimiques agissent en absorbant le rayonnement lumineux ; on distingue les filtres UVB purs et les filtres larges dont le spectre d’absorption s’étend à l’UVA. Les filtres minéraux diffractent ou réfléchissent le rayonnement ; les deux principaux sont le dioxyde de titane (TiO₂) et l’oxyde de zinc (ZnO) ; pour des contingences cosmétiques la taille de leurs particules a été réduite aux nanoparticules. Un PPS doit répondre à des qualités de rémanence, de substantivité et de photostabilité. Deux types de méthodes sont proposés pour l’évaluation des coefficients de protection (CP) des PPS : des méthodes in vivo sur volontaires sains, et des méthodes in vitro utilisant des substrats variés et basés sur la spectrométrie. Le sun protective factor (SPF) in vivo est le CP UVB universellement admis ; pour le CP UVA, la méthode in vivo de la persistent pigment darkening (PPD), bien que non consensuelle, reste à ce jour la plus utilisée en Europe. La mesure de la longueur d’onde critique (Lc) a un intérêt majeur pour définir l’étendue de la protection dans les UVA longs les plus délétères. Les filtres chimiques sont connus pour être à l’origine de réactions locales ; un risque particulier pour l’octocrylène a été évoqué ces dernières années. Récemment, le débat s’est surtout centré sur le risque de perturbations endocriniennes (effet mimant l’estradiol après administration orale à très forte dose chez le rat) pouvant être induites par certains (mais pas les autres !) filtres chimiques, essentiellement le 4-méthylbenzylidène camphre et les benzophénones. Le risque humain paraît peu pertinent dans des conditions normales d’usage de PPS ; le risque environnemental de certains filtres, s’il était avéré, relèverait probablement de leur présence dans bien d’autres produits que les PPS. Les filtres minéraux, souvent prônés chez l’enfant, soulèvent la question du risque des nanoparticules. En tout état, dans le cadre du « Plan d’action national sur la fertilité » et d’une évaluation du risque des nanoparticules, l’Afssaps/ANSM a donné les recommandations adéquates concernant l’incorporation de ces filtres, chimiques et minéraux, dans les produits cosmétiques et le bon usage des PPS. Enfin, les données actuelles ne laissent pas à penser que les PPS puissent avoir un effet délétère en inhibant les effets bénéfiques du soleil, en particulier la synthèse de vitamine D. Les PPS ont démontré, sous couvert d’une utilisation correcte, une efficacité protectrice contre la plupart des effets délétères du soleil à condition d’être conçus en respectant le cahier des charges parfaitement identifié dans les recommandations européennes de 2006. En particulier, les études épidémiologiques démontrent leur efficacité dans la prévention primaire de tous les CC qu’il s’agisse des expositions environnementales ou intentionnelles, et des PPS de protection moyenne suffisent pour cela. Les risques plus que spéculatifs ne doivent certainement pas conduire à dissuader de les utiliser.
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Dans l’Union européenne, les produits de protection solaire ont longtemps été considérés comme des cosmétiques alors que dans d’autres parties du monde, aux États-Unis par exemple, il s’agit de médicaments. En France, des antisolaires disposant du statut de dispositif médical sont récemment apparus. Nous avons voulu comparer des dispositifs médicaux antisolaires à des cosmétiques antisolaires.
Quatre protecteurs solaires ont fait l’objet de tests in vitro afin de déterminer leur efficacité dans les domaines UVB et UVA, ainsi que leur photo-stabilité et leur résistance à l’eau. Il s’agissait de deux produits cosmétiques (Dépiwhite S Soin photoprotecteur^® SPF 50+ et Urgo cicatrices^® SPF 30) et de deux dispositifs médicaux (DM) de classe I (Actinica lotion^® et Kelo-cote UV^® Gel pour cicatrices). Le principe de la méthode in vitro utilisée repose sur la mesure de la transmittance d’un échantillon de produit appliqué sur une plaque de poly(méthacrylate de méthyle), à l’aide d’un spectrophotomètre à sphère d’intégration. Nous avons pu ainsi déterminer le SPF de ces différents produits, leur photo-stabilité et leur niveau de résistance à l’eau.
Du point de vue de l’efficacité, trois des quatre produits testés respectent les recommandations concernant les produits solaires en Europe, à savoir un ratio entre la protection dans le domaine UVB et celle dans le domaine UVA inférieur ou égal à 3 et une longueur d’onde critique (λ_c) supérieure ou égale à 370 nm. C’est le produit Actinica lotion^® qui est le plus efficace, mais aussi le plus photo-stable, tout au moins dans le domaine UVB, des deux DM testés. Les quatre produits testés s’avèrent résistants à l’eau.
Des produits présents sur le marché sous des statuts différents, avec des allégations différentes, présentent dans les conditions de notre étude des propriétés filtrantes équivalentes.
Within the European Union, sun protection products have long been considered cosmetics whereas in other parts of the world, such as the United States, they are considered as medicinal products. In France, sun protection products with medical device status have recently appeared. Our aim was to compare medical and cosmetic sun protection products.
We subjected 4 sun protection products to in vitro testing in order to determine their efficacy in the UVB and UVA ranges, as well as their photo-stability and water resistance. We tested two cosmetic products (Dépiwhite S Soin photoprotecteur^® SPF 50+ and Urgo cicatrices^® SPF 30) and two class I medical devices (MD) (Actinica lotion^® and Kelo-cote UV^® Gel for scars). The main in vitro method used involved measuring the transmittance of a sample of each product applied to a dish containing poly(methyl methacrylate) using a spectrophotometer with integrating spheres. This method enabled us to determine the SPF of the various products as well as their photo-stability and degree of water resistance.
Regarding efficacy, three of the four test products met the European recommendations governing sun protection products, i.e. a ratio between UVB and UVA protection of 3 or less, and a critical wavelength (λc) of 370 nm or higher. Actinica lotion^® was the more effective of the two medical devices tested, and was also the most photo-stable, at least within the UVB range. All four products tested were water-resistant.
The products tested, while having different status and different claims, exhibited equivalent filtration properties under the study conditions.
Enhancement of UV absorption behavior in ZnO-TiO<inf>2</inf>composites
2016, Boletin de la Sociedad Espanola de Ceramica y Vidrio
The ultraviolet–visible, UV–vis, absorption edge behaviour of semiconductor oxides as TiO₂ and ZnO promotes their use as inorganic UV filters for sunscreens. In cosmetics, the use of nanoparticles is favoured because of their higher yield and lower whiteness. However, the particle size effect in the UV absorption is unclear. For this reason, the performances of nano and microsized TiO₂ and ZnO are evaluated in both the UV–vis spectroscopy and the Sun Protection Factor, SPF, value. In order to cover the UV range completely by using inorganic filters a new composite is attempted by dry nanodispersion methodology in which TiO₂ nanoparticles are dispersed onto ZnO microparticles. The new composite shows superior UV absorbing properties and ca. 60% SPF value due to a synergism between components that resulted in extended UV coverage and reduction of the total amount of nanoparticles required in the sunscreens. In addition, nanoparticles are effectively anchored onto microparticles avoiding the presence of free nanoparticles.
El comportamiento del borde de absorción ultravioleta-visible de óxidos semiconductores como el TiO₂ y el ZnO incentiva su uso como filtros inorgánicos para luz UV en cremas solares. En cosmética, el uso de nanopartículas está favorecido por el alto rendimiento que presentan y la baja blancura que aportan a la crema en comparación con las micropartículas. Aun así, el efecto del tamaño de partícula en la absorción de luz en el rango UV no está claro. Por esta razón, el comportamiento de nano y micropartículas de TiO₂ y ZnO se evalúa mediante espectroscopia de luz UV-Visible y mediante el factor de protección solar en cremas. Con el fin de cubrir las necesidades de absorción de luz en todo el rango UV mediante el uso de filtros inorgánicos, se ha generado un nuevo composite mediante un proceso de nanodispersión en seco en el que nanopartículas de TiO₂ se encuentran dispersas sobre micropartículas de ZnO. El nuevo composite presenta propiedades de absorción UV superiores al 60% en lo que al valor de protección solar se refiere. Este hecho es debido a la sinergia entre los componentes de forma que se cubre el rango UV de manera efectiva requiriendo una menor cantidad total de nanopartículas. Dichas nanopartículas se encuentran dispersas de manera efectiva sobre las micropartículas, evitando la presencia de nanopartículas libres.

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Short communicationStudy of the photostability of 18 sunscreens in creams by measuring the SPF in vitro

Abstract

Introduction

Section snippets

Materials

Preparation of sunscreen creams

Results and discussion

J. Chromatogr. A

J. Am. Acad. Dermatol.

Eur. J. Pharm. Biopharm.

Int. J. Pharm.

Photochem. Photobiol.

Ann. Pharmacother.

Short communication
Study of the photostability of 18 sunscreens in creams by measuring the SPF in vitro