Influence of Application Amount on Sunscreen Photodegradation in in vitro Sun Protection Factor Evaluation: Proposal of A Skin‐Mimicking Substrate

Abstract

Widely used polymethylmethacrylate substrates for in vitro sun protection factor (SPF) testing of sunscreens do not mimic the rough surface structure of skin, and in addition, sample loading is less than that used in in vivo SPF testing (2.00 mg cm(-2)). We have developed a skin-mimicking substrate (SMS), which has furrows and ridges on its surface, like human skin. A comparison of the photodegradation profiles of sunscreens on commercially available substrates (including SMS) at the recommended application amounts, and on SMS at various application amounts showed that the photodegradation rate of photounstable sunscreen was dependent on the application amount being higher at lower application amounts. SMS at the recommended application amount of 2.00 mg cm(-2) provided in vitro SPF values that were comparable with in vivo SPF values. Our results confirm that, in order to develop a reliable in vitro SPF method, which is consistent with in vivo SPF determination, it is important to use the same application amount of sample as in the in vivo method, in order to take proper account of sunscreen photostability.

A new hair follicle-derived human epidermal model for the evaluation of sunscreen genoprotection

“…Moreover, determination of SPF is a tedious and time-consuming process that requires participation of human volunteers. Numerous works have been devoted to the development of in vitro techniques as complementary tools to SPF [6][7][8][9][10][11][12][13][14][15]. These approaches mostly rely on the induction of UVB and/or UVA-activated molecular pathways in cutaneous cells as endpoints for the evaluation of the photoprotection afforded by sunscreens following topical application.…”

Skin Surface Topography and Texture Analysis of Sun-Exposed Body Sites in View of Sunscreen Application

“…It has been suggested, for example, that a large volume of skin furrows has a negative impact on sunscreen film homogeneity [21] and that particulate UV filters accumulate overwhelmingly in skin furrows [22]. Furthermore, photodegradation of UV filters was found to depend on the applied amount and indirectly on the topography of the substrate [23]. Existing evidence, therefore, implies that skin topography should be taken into consideration for achieving the desirable sun protection factor (SPF).…”

Development of a Synthetic Substrate for the in vitro Performance Testing of Sunscreens

“…The amount of product applied [7,8], the application procedure [9], the force applied during spreading [10,11], and the type of in vitro substrate have all been shown to impact the in vitro SPF value. Especially careful consideration has been given to the effect of the substrate for SPF measurement, especially its origin, either biological or synthetic [4,12,13,14], its roughness [15], and its surface properties, indicating the affinity of the sunscreen for the in vitro substrate [16]. A substrate made from polymethylmethacrylate (PMMA) is currently favored as it is easy to handle, does not require any preparation, and can be manufactured reproducibly [4].…”