OBJECTIVE: The SPF (sun protection factor) is the best known reference in the world for expressing UVB protection. The SPF is used for labelling purposes for consumer guidance. The determination of the SPF is often accomplished using an in vivo method that has been standardized. Only one in vivo SPF value from one laboratory is required for claiming an SPF value. The aim of this study was to determine the relevance of the in vivo SPF value in terms of interlaboratory variability for claiming purposes and to determine whether some minimum number of different in vivo SPF values from different laboratories would improve the reliability of the final SPF claimed. METHODS: A large population of 44 different commercially available sunscreen formulations from the European market has been investigated, covering various product types. The majority of the SPF values claimed ranged from 15 to 50+. For each product, at least three different in vivo SPF values tested in different laboratories have been gathered, and a variety of statistical analyses have been performed. RESULTS: For each SPF category from the average of all samples, the minimum and maximum in vivo-measured SPF values from the different laboratories would lead to labels claiming different levels of SPF for the same product. Indeed, with coefficients of variation for in vivo SPF determinations that exceed 50% in some cases, as an example, the same product could in reality be claimed to be SPF 30, SPF 50 or SPF 50+. CONCLUSION: In this study, the authors demonstrated that using only one in vivo SPF value from one laboratory may actually challenge the reliability of the final SPF claim significantly. To reduce the consumer health risk by ensuring the reliability of the SPF claim, an average from at least 3 (ideally 4) different in vivo SPF values should be compulsory.R esum e OBJECTIF: Le FPS (Facteur de Protection Solaire) est la r ef erence la plus connue dans le monde exprimant la protection UVB. Le FPS est utilis e a des fins d' etiquetage pour l'orientation des consommateurs. La d etermination du FPS est souvent effectu ee en utilisant un proc ed e in vivo qui a et e normalis e. Afin de revendiquer un niveau de protection, une seule valeur de FPS in vivo issue d'un seul laboratoire est n ecessaire. Le but de la pr esente etude est de d eterminer la pertinence de la valeur du FPS in vivo en termes de variabilit e inter-laboratoire a des fins de revendication et de d eterminer si un minimum de diff erentes valeurs de FPS in vivo provenant de diff erents laboratoires pourrait am eliorer la fiabilit e du FPS revendiqu e. METHODES: Une grande population de 44 diff erentes formulations de protection solaire disponibles sur le march e Europ een a et e etudi ee, couvrant les diff erents types de produits et la majorit e des FPS revendiqu ee variant de 15 a 50+. Pour chaque produit au moins trois diff erentes valeurs de FPS In vivo test es dans diff erents laboratoires ont et e recueillies et une vari et e d'analyses statistiques ont et e r ealis ees. RESULT...

The aim of the study was to develop a simple reproducible and reliable in vitro water resistance (WR) method to assess the sun care products. This paper is the result of a scientific collaboration between seven different international industrial laboratories and testing institutes. The same group has already achieved an in vitro protocol for the sun protection factor (SPF) determination [1]. The in vitro WR of sunscreens was tested by applying the same principle as in vivo, which determines the percentage of retention of sunscreen products by assessing the SPF before and after water immersion. Special care was taken to study the parameters influencing the WR and the possibility to follow the kinetics of sunscreen retention during water immersion. The influence of different water qualities has been tested, and osmosed water (1-3 microS cm(-1)) was chosen for the main ring study. Measurement was carried out after 5, 20 and 40 min of immersion. Histograms of selected products demonstrate the percentage of WR at all measuring times and centres, and the regression coefficient to the in vivo determination was shown and statistical calculations clearly demonstrate the reproducibility of the results between the different evaluation centres. The presented method is a practical, convenient and relevant tool for WR screening of sun care and skin care products. It even has the potential to be the starting point for the replacement of the in vivo method in future.

Synopsis OBJECTIVE: Development of an international harmonized in vitro method for sun protection factor (SPF) assessment is currently in progress because of the lack of both reproducibility and accuracy in the current methodology. The aim of this article was to focus on the principle and mathematical aspects (Part I) of a new approach for a reproducible and correlated in vitro test method to obtain results similar to the in vivo SPF for labelling purposes. METHODS: The currently used in vitro test is based on the spectroradiometric measurement of the residual ultraviolet (UV) transmitted through a thin layer of sunscreen spread on a substrate. To reach the goals of reproducibility and accuracy, the specifications of the key parameters and different steps of the procedure are clearly described in this study. RESULTS: Once reproducibility is obtained with an ad hoc procedure, the accuracy of the SPF values for a large number of products can be demonstrated with the prerequisite of a single UV irradiation dose and a multisubstrate solution. Using a total of 27 samples, the mean coefficient of variation was found to be <10% and the coefficient of correlation with the SPF clinical value reached approximately 0.81. CONCLUSION: The first part of the article revealed a relevant tool for the in vitro SPF assessment that can be closely correlated to the in vivo SPF for labelling purposes. The second part study will focus on the practical aspects and implementation (Part II) achieved using the present method, will validate the robustness of the models and demonstrate the need to have different product categories to reach a reliable in vitro SPF method adaptable for all products available in the market.

Our second paper concludes that the new in vitro SPF method (based on 113 sunscreen products from the Parts I and II) is clearly adaptable for the SPF labelling purpose on any product type because it is non-invasive, less expensive, more practical and more reliable if performed under strict conditions.

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