SUN CARE
Testing standards for evaluating sun care
Anne Charpentier – Skinobs
Evaluating the performance of sun protection is a complex issue embracing in silico, in vitro, in vivo and hybrid testing methods that are at least as important as the formulation itself. First, it is interesting to consider the main
criteria that influence the performance of UV protection products, e.g. composition, repartition, photostability, absorbance and distribution of inorganic and organic filters, galenic (spray, compact powder, oil, cream etc.) and other properties to form a stable, homogeneous and resistant product that is pleasant to apply. Furthermore, in real-world conditions, the
performance of sun care is impacted by other criteria such as wrinkles, skin locations, sweat, hair, application procedures and the quantity of product used.
A complex environment of tests Technically, it seems important to increase the reproducibility and the accuracy of in vitro and in vivo testing by implementing systematic control testing such as Bipea (the French interprofessional bureau of analytical studies) inter-laboratory comparison tests and audits of global processes such as Suncert diagnostics and FEBEA (Federation of Beauty Enterprises) audits.
The gap between standardised applications
versus real-world conditions may also be deeply studied, including anti-salt, anti-sweat or anti-sand claims substantiation. Among the available clinical study methods, in vitro SPF is strongly required by the industry and governmental organisations, delivering results equivalent to in vivo SPF according to the ISO 24444 method. To gather sufficient evidence, the degree
of protection should be measured using standardised, reproducible testing methods and take photo-degradation into account - as recommended by the European Commission. From an ethical point of view, the
application of erythema on the subjects which causes skin damages does not seem to be a long-term solution for UVB assessment. Fortunately, the hybrid diffuse reflectance spectroscopy (HDRS) method or in vitro method should propose a new perspective within the next few years. Are the various damages that UVB, UVA,
blue light, infrared may cause to the skin a target for new claim substantiation? Beyond anti-sun spectrum objectivation, and index
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determination, can we evaluate complementary photo-ageing performances such as antioxidants, anti-free radicals, anti-ageing, anti-dark spots etc.?
A wide range of validated methods Nowadays, there are different sunscreen testing procedures for claiming the SPF, UVA protection factor (UVAPF), critical wavelength (CW), water resistance (WR). Fortunately, mainly due to the ISO (International Organization for Standardization), standards are available to harmonise these methods worldwide. 1. In vivo testing ■ SPF, according to ISO 24444 ■ UVAPF, according to ISO 24442 ■ WR, procedure according to ISO 16217 ■ WR, percentage calculation according to ISO 18861 Until now, the SPF value given on the
bottle of each sun protection product must be
determined by the generation of sunburn on the backs of at least ten volunteers. This is not only invasive but also time-consuming because volunteers must come back after 24 hours for evaluation of the minimal erythemal dose. 2. In vitro assays ■ UVAPF-CW, according to ISO 24443 ■ SPF, according to ISO 23675 The main points of vigilance are: the
control of the topographic parameters of the substrates, the temperature of the interface substrate/sample, the homogeneous and reproducible spreading (HD-Spreadmaster is highly recommended), the drying step, the acquisition of the initial UV absorbance spectrum by a spectrophotometer (including specific calibrations), and two UV absorbance measurements to calculate the final in vitro SPF. 3. Hybrid assays ■ In vivo/in vitro, hybrid diffuse reflectance spectroscopy SPF-UVAPF, according to ISO 23698 (under validation)
October 2022 PERSONAL CARE
85
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