The future of sunscreen efficacy evaluation

by Felicia Maria Syring

Institution: Freie Universität Berlin
Degree: PhD
Year: 2015
Record ID: 1101814
Full text PDF: http://edocs.fu-berlin.de/diss/receive/FUDISS_thesis_000000098022


The sun protection factor (SPF) has been the internationally accepted standard characterizing sunscreen efficacy for the past decades. This factor is based solely on prevention of erythema, principally induced by UVB irradiation. However, UVA and even visible and infrared radiation have been equally implicated to contribute towards sun induced skin damages, thereby highlighting limitations implied with the use of the SPF as single indicator. Alternative efficacy indicators, providing a more comprehensive approach for characterization, have been proposed. The aim of this study was to determine the protective efficacy of sunscreen utilizing two of these alternative indicators, the spectroscopic universal sun protection factor -USPF- and the radical formation ratio -RF-, calculated based on electron paramagnetic resonance measurements. By comparing these results to SPF values, provided by an outside institution, conclusions regarding capabilities and limitations of both efficacy indicators could be drawn. Five specially developed formulations, containing commonly utilized active ingredients - chemical filters, physical filters and antioxidants, which exhibit different mechanisms of action, were evaluated in changing composition. As expected, chemical filters were shown to provide a protective effect measurable by each method utilized. When physical filters were investigated as single active ingredient, USPF and SPF values increased. Due to the relatively low amount (2%) of physical filter contained in the formulations and a possible interaction of physical filters with antioxidants, leading to a decrease in antioxidant capacity, no clear conclusion could be drawn when physical filters were utilized in combination. Antioxidants were shown to significantly increase SPF values. As anticipated, this effect failed to appear in the solely spectroscopically based USPF values. However, there was also no effect observed for RF values, possibly attributable to the high radiation intensity used in the ex vivo setting, obliterating antioxidants early on. A comparison of determined USPF values with previous results from sunscreen formulations containing similar compositions of active ingredients confirmed the expected linear correlation for USPF and SPF values. The values obtained verify the significance of USPF values for objective evaluation of sunscreen efficacy over the entire UV spectrum, independent of biological responses. In combination with the RF for infrared and visible ranges, these indicators could lead to a more comprehensive sunscreen characterization. The results of this study provide important information regarding effectiveness and capabilities of the investigated efficacy indicators, but also highlight the need for further research to eventually implement altered, more comprehensive efficacy indicators in international sunscreen evaluation standards. Der Lichtschutzfaktor SPF ist aktuell die anerkannte Größe zur Kennzeichnung der Wirksamkeit von Sonnenschutzmitteln. Dieser Faktor beruht allein…