In vitro standard methods are available and accepted worldwide to assess UVA protection of sunscreen products. Though, harmonisation of methods has made progress in the last decade, still two differing methods - one by FDA the other by ISO - are in use. In a multicentre study including 9 centres in Germany, 4 different commercial sunscreen products were assessed using both methods to discover their similarities and differences. UVA protection factor and Critical Wavelength were detected at various substrate type (sandblasted versus moulded PMMA plates), at different surface roughness of the plates as well as at different product application dose using two different irradiation spectra. Results: The strongest influence on UVA protection factor results from the surface roughness of the plates. Depending on the roughness (accepted range of 2 to 7 gm in the FDA method) a variability in the UVA protection factor of up to 25% was observed, while the much narrower definition of plate roughness by ISO (4.5 to 5.2 mu m) had no relevant influence on the test results. Sandblasted plates in our assessment led to higher UVA protection factors and produced less scattered results compared to moulded plates. These differences were not pronounced. Application dose and spectra of the irradiation source were of negligible influence on UVA protection factor results for the investigated UV-filter combinations. The UVA protection factor which is the endpoint of the ISO method was found to be a parameter with a high potential to differentiate among different test products. The endpoint of the FDA method - the Critical Wavelength - was found to be an unambitious endpoint. Insensitivity to all described modifications of the method was observed. All investigated products performed similar and passed the Critical Wavelength criteria independent of method and parameters.

In the past, several attempts have been made to develop in vitro methods for determining protection against UV radiation. To date however, there is no broadly accepted method. Various known and unknown parameters influence the transmission measurements of scattering films, such as the multifaceted compositions of sunscreens, the technical limitations of measurement devices as well as the difficulty to apply very thin films of sunscreen in a reproducible manner throughout different laboratories. In vitro data were measured in this multicenter study to compare possible methodologies and strategies for an in vitro approach to the sun protection factor (SPF). This publication will not present a final in vitro SPF test method, but it will point out which technical side effects may influence such a method. Influential factors such as the quality of spectrophotometer used, the amount of product applied, pretreatment of samples, time and temperature of equilibration, size of the measured surface, the application process or the calculation on the basis of standardized data are presented and discussed. Finally, a reduction of the standard deviations within single laboratories could be realized for in vitro SPF testing, but no improvement of the interlaboratory comparison was obtained. The development of a valid and reliable SPF in vitro test still remains a challenge, and further work is necessary to develop a satisfactory method.

It is often debated that the protection against solar-induced erythema under real conditions is dependent upon the amount of sunscreen applied. It is believed that when too little is applied a lower sun protection than indicated on the label will result. The aim of this study was to quantify this effect. In this multicenter study, the influence of three different amounts (0.5, 1.0, 2.0 mg/cm2) of three commercial sunscreen products in three reliable test centers was investigated according to the test protocol of The International Sun Protection Factor Test Method. The main result was a linear dependence of the SPF on the quantity applied. Taking into consideration the volunteer-specific variations, an exponential dependence of confidence interval of the in vivo SPF and amount applied was found. The highest amount applied (2.0 mg/cm2) was linked to the lowest confidence intervals. Thus, from the point of view of producing reliable and reproducible in vivo results under laboratory conditions, the recommendation of this multicenter study is an application quantity of 2.0 mg/cm2.

Background/Purpose: UVA protection of sunscreen formulations is becoming increasingly important especially because of recent investigations on the long-term skin damage associated with UVA light. The development of a new in vitro method to measure UVA protection performance made it possible to predict reliably the in vivo UVA protection performance of representative sunscreen formulations found presently in the European and US market (1). This study was performed in order to determine the applicability of the method developed by Wendel et al. (1) to photostable and photolabile filter combinations and in order to measure the influence of sample pre-irradiation on predicting the in vivo performance. This was done by subjecting six photostable and six photolabile filter combinations to a standard irradiation. Then the in vitro UVA protection afforded by each combination was measured and compared with the persistent pigment darkening (PPD) values determined in vivo .Results: The results clearly showed that pre-irradiation does not affect the in vitro PPD factor of the photostable and photolabile samples in the same way. Almost identical values were determined for the stable filter combinations with and without pre-irradiation, whereas distinct reductions in the in vitro factors by as much as 93% were observed after irradiation in the group of less stable filter combinations. Comparison of the in vivo and in vitro PPD factors showed that all 12 samples comprise a homogeneous distribution with identical factors before irradiation. After pre-irradiation only the factors for the six less stable products were selectively reduced. The correlation with the data determined on the skin was clearly poorer for these products after irradiation.Conclusion: Overall, the results showed that pre-irradiation should not to be used for the assessment of UVA protection using this method. Furthermore, it can be assumed that normalizing the in vitro absorbance curves to the labelled SPF of the sunscreen will adequately take into account the photochemical behaviour of UV filters on the skin during sun exposure.

Synopsis The in vitro determination of the UV protection of sunscreens is usually performed by means of transmission measurements with special photometers. Many different instruments are used. Besides numerous commercially available instruments, which are equipped by the manufacturer for the specific measurement, other modular instruments are used. We present here a quick and practical method to evaluate the performance of these instruments with respect to their measuring ranges and to compare the uniformity and reliability of the results obtained with these instruments.

Hoppe U., Lübeck, Germany Jacobi Ute, Martinsried, Germany Kalia Y.N., Archamps, France Kemeny Lajos, Szeged, Hungary Koch Stefan, Bad Saarow-PIeskow, Germany Korting Hans-Christian, München, Germany Kragballe Knut, Aarhus, Denmark Krakhecke A.G., Mato Grosso do Sul, Brazil Kramer Axel, Greifswald-Eldena, Germany Mahrle G., Köln, Germany Maibach Howard I., San Francisco, Calif., USA May Ekkehard, Berlin, Germany Meffert Hans, Berlin, Germany Messenger A., Sheffield, United Kingdom Middelkamp Maritza, Amsterdam, The Netherlands Mukhtar Hasan, Madison, Wisc., USA Neubert Reinhard H.H., Halle, Germany Nohynek Gerhard, Asnieres, France Pardon M.C., Paris, France Parra Juez José Luis, Barcelona, Spain Philips Neena, Heverlee, Belgium Potapenko A.Y., Moscow, Russia Rogiers Vera, Brussels, Belgium Rudolph Thomas, Darmstadt, Germany Ahmad Nihal, Madison, Wisc., USA Ahsan Haseeb, Madison, Wisc., USA Altmeyer Peter, Bochum, Germany Andersen Klaus, Odense, Denmark Astner Susanne, Berlin, Germany Baron J.M., Aachen, Germany Benfeldt Eva, Hellerup, Denmark Bernard Bruno A., Clichy, France Bimczok Rudolf, Darmstadt, Germany Bito T., Berkeley, Calif., USA Blume-Peytavi Ulrike, Berlin, Germany Böhm Markus, Münster, Germany Borges C.R., Salt Lake City, Utah, USA Butz T., Leipzig, Germany Coffey G.P., South San Francisco, Calif., USA De Paepe Kristien, Brussels, Belgium Eady Anne E., Leeds, United Kingdom Elsner Peter, Jena, Germany Fluhr Joachim, Jena, Germany Gers-Barlag Heiner, Hamburg, Germany Ghannoum M.A., Cleveland, Ohio, USA Gollnick Harald M., Magdeburg, Germany Hadgraft Jonathan J., Chatham in Maritime, United Kingdom Heinrich Ulrike, Witten, Germany Herzog Bernd, Grenzach-Wyhlen, Germany Hipler Uta-Christina, Jena, Germany

UVA protection provided by sunscreens is an issue of major importance due to increasing knowledge about UVA-induced skin damage. In Europe there is no officially accepted method to determine the level of UVA protection. The objective of the present study was to develop a new method combining the merits of an in vitro model, which is simple and reproducible, with the required information of in vivo efficacy. For the in-vitro part of the method transmission measurements were carried out through thin layers of product sample on roughened PMMA-plates (Plexiglas®). The amount of sunscreen was adjusted to the roughness of the plates to ensure an optimal distribution of the sample and measurement in the optimal range of the spectrophotometer. Mathematical normalisation of the absorption spectrum to the label (in vivo) SPF makes it possible to predict the level of in vivo UVA protection. Furthermore, this new method shows a very good correlation with in vivo results for the UVA protection performance (PPD) of 45 different commercial sunscreens. A method is described that is suitable for predicting the UVA protection delivered by sunscreens, which should be considered in any future official discussion on UVA methodology.

Synopsis The UVA protection delivered by sunscreens is an issue of increasing importance due to the increasing knowledge about UVA‐induced skin damage. In Europe there is no officially accepted method available to determine the degree of UVA protection. Therefore, the objective of the present study was to design a protocol combining the merits of an in vitro model, which are simple and reproducible, with aspects known to be relevant from in vivo studies. The principle is: an UV‐transparent support to which the test product is applied, a (pre)irradiation and a transmission measurement. Transpore® tape (standard support for SPF determinations) was found to be incompatible with many preparations on prolonged contact times. Roughened quartz was adopted as a suitable alternative. Transmission measurements on this support are not reliable with a layer of 2 mg cm−2 (standard for SPF) due to detection limitations of spectrophotometers, hence a reduced layer of 0.75 mg cm−2 was adopted. Overall, it is very difficult to apply products in a reproducible thin layer on appropriate substrates. As a consequence, absolute parameters derived from the transmission profile show relatively large dispersion, whereas relative parameters, such as critical wavelength λc[1] or UVA/UVB ratio are much less sensitive to unavoidable variations in layer thickness. An increase in deviations was observed when the samples were irradiated before measurement. It is crucial to control the output carefully (spectral distribution and even more importantly, irradiance and dose delivered) of the light source. By doing so and also taking into account the previous learning steps, a protocol was drafted and tested in a ringtest (four samples in six laboratories). The results are encouraging and show that if relative parameters (e.g. λc, UVA/UVB ratio) are considered, the intra‐ as well as interlaboratory reproducibility is clearly better than can be obtained in vivo.In general, we describe a suitable method, which can be considered in any future official discussions about the methodology to determine UVA protection. Résumé La protection contre les UVA apportée par les écrans solaires est un sujet d’importance croissante en raison de la progression des connaissances concernant les dommages à la peau causés par les UVA. En Europe il n’existe pas de méthode disponible officiellement reconnue pour déterminer le degré de protection contre les UVA. Par conséquent, l’objectif de la présente étude est de concevoir un protocole associant les avantages d’un modèle in vitro, qui est simple et reproductible, avec des aspects connus comme appartenant aux études in vivo. Le principe est le suivant: un support transparent aux UV auquel le produit testé est appliqué, une (pré)irradiation et une mesure de transmission. Le ruban Transpore® (support standard pour la détermination des SPF) se révèle incompatible avec de nombreuses préparations lors de temps de contact prolongés. Le quartz rugueux est adopté comme alternative appropriée. Les mesures de transmission sur ce support ne sont pas fiables avec une couche de 2 mg/cm2 (norme pour les SPF) en raison des limites de détection des spectrophotomètres, et on adopte donc une couche réduite de 0,75 mg/cm2. Il est surtout très difficile d’appliquer des produits en une couche fine reproductible sur des substrats appropriés. En conséquence, les paramètres absolus tirés du profil de transmission montrent une assez grande dispersion, tandis que les paramètres relatifs, tels que la longueur d’onde critique λc[l] ou le rapport UVA/UVB sont beaucoup moins sensibles aux variations inévitables de l’épaisseur de la couche. On observe une augmentation des écarts lorsque les échantillons sont irradiés avant la mesure. Il est crucial de contrôler soigneusement la sortie (distribution spectrale et encore plus important, irradiation et dose délivrée) de la source lumineuse. Dans ces conditions, et en tenant aussi compte des enseignements des étapes précédentes, un protocole a étéébauché et testé lors d’un essai tournant (quatre échantillons dans six laboratoires). Les résultats sont encourageants et montrent que si on considère les paramètres relatifs (par exemple λc, rapport UVA/UVB), la reproductibilité intra et interlaboratoires est clairement meilleures que ce qu’on peut obtenir in vivo.D’une façon générale, nous décrivons une méthode appropriée, qui peut être considérée dans tout échange officiel futur concernant la méthodologie pour déterminer la protection contre les UVA.