Quantification of the Inhomogeneous Distribution of Topically Applied Substances by Optical Spectroscopy: Definition of a Factor of Inhomogeneity

Journal of Biophotonics

et al. 2017

Determination of sun protection factors (SPFs) is currently an invasive method, which is based on erythema formation (phototest). Here we describe an optical setup and measurement methodology for the determination of SPFs based on diffuse reflectance spectroscopy, which measures UV-reflectance spectra at 4 distances from the point of illumination. Due to a high spatial variation of the reflectance data, most likely due to inhomogeneities of the sunscreen distribution, data of 50 measurement positions are averaged. A dependence of the measured SPF on detection distance is significant for 3 sunscreens, while being inconclusive for 2 sunscreens due to high inter-sample variations. Using pig ear skin samples (n = 6), the obtained SPF of 5 different commercial sunscreens corresponds to the SPF values of certified test institutes in 3 cases and is lower for 2 sunscreens of the same manufacturer, suggesting a formulation specific reason for the discrepancy. The results demonstrate that the measurement can be performed with a UV dose below the minimal erythema dose. We conclude the method may be considered as a potential noninvasive in vivo alternative to the invasive in vivo phototest, but further tests on different sunscreen formulations are still necessary.

Section: Resultsmentioning

confidence: 81%

Section: Spatial Variation Of Reflectance Values With Sunscreenmentioning

confidence: 79%

Section: Methodsmentioning

confidence: 95%

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Evaluation of detection distance‐dependent reflectance spectroscopy for the determination of the sun protection factor using pig ear skin

Reble

Gersonde

Journal of Biophotonics

et al. 2017

“…The penetration and distribution on skin of the added fluorescent marker might be different than that of the UV filters itself, or the penetration characteristics might be changed, if fluorescent markers like sodium fluorescein are fixed to the substances 19 . The determination of the inhomogeneity factor by tape stripping is strongly dependent on the amount of the topically applied formulation 10,20 …”

Section: Introductionmentioning

confidence: 99%

Electrohydrodynamic spray applicator for homogenous application and reduced overspray of sunscreen

Schleusener

Skin Research and Technology

Wille³

et al. 2020

Background The recommended amount of sunscreen by hand application (2 mg/cm2) is in reality not achieved, which decreases the homogeneity and thereby the effective sun protection factor (SPF). Materials and Methods The homogeneity of sunscreen applied by a newly developed spray applicator using an electrostatically charged aerosol, for which a hand rubbing of the formulation is not necessary, is evaluated. In vivo experiments were performed on the volar forearms of human volunteers using the spray applicator compared to the standardized hand application according to ISO 24444. Results The distribution homogeneity was assessed qualitatively using in vivo laser scanning microscopy and quantitatively by absorption spectroscopy after tape stripping and by the standard deviation of multiple spatially displaced reflectance measurements for non‐invasive SPF determination below the minimal erythemal dose, which showed a significantly higher homogeneity by 20.9% after spray application compared to hand application. Conclusion Non‐invasive SPF determination of multiple spatially displaced reflectance measurements was proven to be a suitable method for the non‐invasive determination of the sunscreen distribution homogeneity. Electrostatically charged spray application increased the sunscreen distribution homogeneity on the skin and can reduce the amount of overspray.

“…Based on erythema formation, it is a measure of how long sun exposure can be prolonged before sunburn is induced. However, by employing erythema formation as a single efficacy indicator, one not only neglects the consequences of radiation in volunteer testing but also focuses on a single biological process, which is predominantly induced by ultraviolet B (UVB) radiation [1,2,5]. Damage known to be induced by ultraviolet A (UVA) and even infrared (IR) and visible (VIS) radiation [6,7,8] can only be insufficiently accounted for by applying the SPF.…”

Section: Introductionmentioning

confidence: 99%

Investigation of Model Sunscreen Formulations Comparing the Sun Protection Factor, the Universal Sun Protection Factor and the Radical Formation Ratio

Syring

Weigmann²,

et al. 2015

Skin Pharmacol Physiol

In view of globally rising skin cancer rates and harmful effects exerted by sunlight throughout the ultraviolet, visible and infrared ranges, an objective, safe and comprehensive method for determining sunscreen efficacy is required in order to warrant safe sun exposure. In this study, the influence of characteristic active ingredients (chemical filters, physical filters and antioxidants) on different sunscreen indicators, including the universal sun protection factor and the radical formation ratio, was determined and compared to their influence on sun protection factor values. Spectroscopic universal sun protection factor measurements were conducted ex vivo by analyzing tape strips taken from human skin, and radical formation ratio determination was performed via electron paramagnetic resonance spectroscopy using porcine ear skin ex vivo. The sun protection factor determination was conducted according to ISO standards (ISO 24444:2010). It was shown that chemical filters provide a protective effect which was measurable by all methods examined (spectroscopy, electron paramagnetic resonance spectroscopy and erythema formation). Physical filters, when used as single active ingredients, increased protective values in universal sun protection factor and sun protection factor measurements but exhibited no significant effect on universal sun protection factor measurements when used in combination with chemical filters or antioxidants. Antioxidants were shown to increase sun protection factor values. Radical formation ratio values were shown to be influenced merely by chemical filters, leading to the conclusion that the universal sun protection factor is the most suitable efficacy indicator for the ultraviolet range.