Introdução: o fator de proteção solar (FPS) dos filtros solares é determinado in vivo pela aplicação de uma quantidade padrão de 2mg/cm². Na prática, os usuários aplicam uma quantidade menor e de maneira irregular o que afeta o FPS final. Modelos matemáticos mostram que a reaplicação do fotoprotetor resulta em um aumento de 15-40% na capacidade de proteção à radiação ultravioleta. Objetivos: avaliar se a reaplicação de filtro solar aumenta a quantidade e melhora a regularidade do filme do produto na pele. Métodos: os voluntários selecionados foram solicitados a aplicar um filtro solar padronizado composto por benzofenona 6% (FPS 6) em ambos antebraços previamente lavados com sabonete neutro. Após 30 minutos o fotoprotetor foi reaplicado em um antebraço, selecionado previamente por computador para evitar a influência do lado dominante. Cinco fitas adesivas foram coletadas de duas diferentes áreas de cada antebraço, 30 minutos após a primeira aplicação e 30 minutos após a reaplicação. A concentração de benzofenona foi medida por cromatografia líquida de alta eficiência e a quantidade do filtro estimada por correlação matemática entre a quantidade de benzofenona removida nas fitas e a concentração na formulação. Resultados: um total de 107 voluntários, com idades entre 18 e 35 anos, foram selecionados. Entre eles, 36 participaram da parte prática do estudo (21 mulheres e 15 homens, idade média de 22,6 anos) A mediana da quantidade do filme de filtro solar aplicado à pele com 1 aplicação foi de 0,43mg/cm² (0,17-1,07) e com 2 aplicações foi de 0,95mg/cm² (0,18-1,91) e essa diferença foi considerada estatisticamente significativa (p=0,002). A variação comparando a uniformidade do filme com 1 e 2 aplicações não foi significativa (p=0,423). Conclusões: a reaplicação de filtro solar resulta em uma melhora da quantidade de produto aplicado à pele, refletindo, provavelmente, em uma melhora da proteção à radiação ultravioleta. Contudo, mesmo com a reaplicação a quantidade mediana foi inferior à preconizada (2mg/cm²) e não foi uniforme, confirmando que o fator de proteção real é muito inferior ao estabelecido no rótulo do produto. Os resultados reforçam a recomendação de reaplicar o produto para atingir um melhor nível de fotoproteção. / Background: the sun protection factor (SPF) of sunscreens is determined in vivo by the application of a standard amount of 2mg/cm², under controlled conditions. Individuals usually apply a smaller and irregular amount, compromising the final sun protection. Theoretical models show that sunscreen reapplication results in an increase of 15% to 40% in the UV protection capacity. Objective: to verify how young individuals use the filter and whether its reapplication increases the amount and regularity of the product in the skin, under real conditions. Methods: the selected volunteers were asked to apply a standardized sunscreen with 6 % benzophenone on both forearms. After 30 minutes, the sunscreen was reapplied in one of the forearms. Five tape-strips were collected from 2 different sites in each forearm, 30 minutes after the first application and 30 minutes after reapplication. The concentration of benzophenone was measured by liquid chromatography and the quantity of filter was estimated by calculating the correlation between the amount of benzophenone that was removed by the tapes, and the quantity present in the formulation. Results: A total of 107 volunteers, with ages between 18 and 35 years, were selected. Among them, 36 volunteers (21 female and 15 male, mean age 22.6 years) participated in the practical part of the study. The overall median sunscreen amount was 0,43mg/cm² (0.17–1.07) with 1 application and 0.95mg/cm² (0.18-1.91) with 2 applications, and the difference between sites was significant (p=0,002). The variation comparing the uniformity of the film with 1 and 2 applications was not significant (p=0,423). Conclusion: the reapplication of sunscreen contributes for a better amount of the product in the skin, probably reflecting in a better sun protection. However, even with reapplication, the median amount was less than the recommended one (2mg/cm²) and not homogeneous, confirming that the real level of protection is much lower than the stated SPF of the product. The results support the recommendation for reapplying filters to obtain a more reliable chemical photoprotection.

Zielsetzung dieser Arbeit war es, das Verhalten der in modernen Sonnenschutzmitteln eingesetzten Titandioxid-Mikropartikel mit quantitativen Methoden zu bestimmen, um Aussagen über ihre Eignung zu erhalten. Dabei stand die Frage nach der Verteilung der Substanz innerhalb des Stratum corneum im Mittelpunkt der Untersuchungen. Insbesondere war wegen der bekannten photokatalytischen Aktivität von Titandioxid zu klären, ob ein Kontakt mit den lebenden Bereichen der Haut ausgeschlossen werden kann. Für die Messungen wurden zwei kommerziell genutzte, unterschiedlich beschichtete Titandioxid-Mikropartikel eingesetzt. Eine wesentliche Voraussetzung für diese Untersuchungen war die Anwendung der Abrissmethode (Tape stripping) in Kombination mit der spektroskopischen Bestimmung der Extinktion im sichtbaren Bereich zur Berechnung des Hornschichtprofils. Die Konzentration der Titandioxid-Partikel wurde mit Hilfe von Röntgenfluoreszenz-Messungen bestimmt. So war es erstmals möglich, in vivo standardisierte und reproduzierbare Untersuchungen zum Penetrationsverhalten von beschichteten Titandioxid-Mikropartikeln in die Hornschicht der menschlichen Haut durchzuführen. Durch Langzeitapplikation der Substanzen und die Beobachtung der Titandioxid-konzentrationen in der Hornschicht über mehrere Tage konnten auch Aussagen zum Penetrationsverhalten der applizierten Mikropartikel gemacht werden. Es wurde eindeutig gezeigt, dass die untersuchten Substanzen unabhängig von ihrer Struktur, von ihrer Beschichtung und vom Probanden hauptsächlich in den obersten Schichten des Stratum corneum lokalisiert sind. Nach Klärung dieser grundsätzlichen Fragen war es notwendig, die Ursache für das Auftreten extrem geringer Titandioxid-Konzentrationen auf Abrissen zu bestimmen, die aus tieferen Schichten des Stratum corneum entnommen wurden. Durch die Kombination der Abrissmethode mit einem speziellen Färbeverfahren und der Laser-Scan-Mikroskopie ergaben sich deutliche Hinweise auf die Bedeutung der Follikelkanäle für das beobachtete Phänomen. Röntgenspektroskopische Untersuchungen an Biopsien zeigten, dass diese Mikropartikel in die Haarfollikel eindringen und damit Bereiche unterhalb des Stratum corneum erreichen. Hierbei wurden die Mikropartikel in dieser Region nur in Follikelkanälen, nicht aber im Bereich der lebenden Zellen nachgewiesen. Diese Ergebnisse belegen, dass Titandioxid nur in einzelne Follikelkanäle penetriert, eine Aussage, die im Rahmen der vorliegenden Untersuchungen erstmals beschrieben wurde. In Übereinstimmung mit der Zielsetzung der Arbeit konnte unter Einsatz unterschiedlicher Untersuchungsmethoden gezeigt werden, dass die beschichteten Titandioxid-Mikropartikel im oberen Bereich der Hornschicht lokalisiert sind und damit als hocheffiziente Lichtschutzfilter den Schutz der darunter liegenden lebenden Bereiche der Haut garantieren. Der sichere Nachweis der Titandioxid-Mikropartikel innerhalb einzelner Follikelkanäle besitzt grundsätzliche Bedeutung für das Verständnis von Penetrationswegen. / The objective of this work was to determine the behaviour of titanium dioxide microparticles, used in modern sunscreen agents, with quantitative methods in order to receive statements about their suitability. The focal point of the investigations was the question on the distribution of the substance within the stratum corneum. Because of the well-known photocatalytic activity of titanium dioxide, our aim was to clarify whether a contact with the living cells of the skin could be excluded. For these measurements, two commercial titanium dioxide micro particles were used, covered with different coating materials. The calculation of the stratum corneum profile was a substantial prerequisite for these investigations. This was done by application of the tape stripping method in combination with the spectroscopic determination of the absorption in the visible range. The concentration of the titanium dioxide particles on the tape strips was determined by X-ray fluorescence measurements. In this manner it was possible for the first time, to perform standardized and reproducible in vivo measurements to investigate the penetration behaviour of coated titanium dioxide micro particles into the horny layer of the human skin. Predications could be made about the penetration behaviour of the applied micro particles by observation of the titanium dioxide concentrations in the stratum corneum during several days after long-term application of the substances. It could be shown that the examined substances were localized mainly in the upper layers of the stratum corneum, independently of their structure, coating and the volunteers. After clarifying these basic questions, it was necessary to explain the occurrence of extremely small concentrations of titanium-dioxide on tape strips, which were taken from deeper layers of the stratum corneum. This observed phenomenon was investigated by combining tape stripping with a selective staining of the tapes and with laser scanning microscopy. Investigations of a biopsy with x ray fluorescence measurements showed that the micro particles penetrate into the hair follicles, and in this manner reached areas below the stratum corneum. In this region, the micro particles were found only in follicle channels, but not within the area of the living cells. These results prove that titanium dioxide micro particles only penetrate into single follicle channels, a statement, which has been described here for the first time. In agreement with the objective of this thesis, it was shown, that the coated titanium dioxide micro particles were localized within the upper area of the horny layer and as high efficient sunscreen filters consequently guarantee, the protection of the living areas of the skin below. The proof of the titanium dioxide micro particles within individual follicle channels has basic importance for the understanding of the penetration pathways.