In vitro skin model for characterization of sunscreen substantivity upon perspiration

Abstract

Objective The resistance of sunscreens to the loss of ultraviolet (UV) protection upon perspiration is important for their practical efficacy. However, this topic is largely overlooked in evaluations of sunscreen substantivity due to the relatively few well‐established protocols compared to those for water resistance and mechanical wear. Methods In an attempt to achieve a better fundamental understanding of sunscreen behaviour in response to sweat exposure, we have developed a perspiring skin simulator, containing a substrate surface that mimics sweating human skin. Using this perspiring skin simulator, we evaluated sunscreen performance upon perspiration by in vitro sun protection factor (SPF) measurements, optical microscopy, ultraviolet (UV) reflectance imaging and coherent anti‐Stokes Raman scattering (CARS) microscopy. Results and conclusion Results indicated that perspiration reduced sunscreen efficiency through two mechanisms, namely sunscreen wash‐off (impairing the film thickness) and sunscreen redistribution (impairing the film uniformity). Further, we investigated how the sweat rate affected these mechanisms and how sunscreen application dose influenced UV protection upon perspiration. As expected, higher sweat rates led to a large loss of UV protection, while a larger application dose led to larger amounts of sunscreen being washed‐off and redistributed but also provided higher UV protection before and after sweating.

Enhancing the sweat resistance of sunscreens

“…However, despite the fact that sweating is highly probable in many situations where sunscreen is used, such as during outdoor sports activities, and sunbathing, the effect of sweating on the substantivity of sunscreens is rarely directly addressed. Our previous study, which involved an in vitro perspiring skin simulator, showed that the water released from the skin underneath the applied sunscreen film will have a distinct negative impact on the efficiency of the sunscreen 13 . Specifically, our study showed that perspiration reduced the sun protection factor (SPF) by two mechanisms: (1) direct sunscreen wash‐off, which leads to reduced film thickness and (2) redistribution of the sunscreen, which results in less uniformity.…”

“…In this study, we used a perspiring skin simulator, which is described in detail elsewhere 13 . Briefly, the setup comprises a multilayer skin‐mimicking substrate, a chamber located underneath the substrate, a syringe pump, and connecting tubes, as illustrated in Figure 1.…”

“…Briefly, the setup comprises a multilayer skin‐mimicking substrate, a chamber located underneath the substrate, a syringe pump, and connecting tubes, as illustrated in Figure 1. The skin‐mimicking substrate consists of a gelatin‐based skin layer (gelatin, glycerol, and formaldehyde), with a thickness of 250 μm and a surface roughness of 100–200 nm 13 . The gelatin‐based film was applied to a polymethylmethacrylate (PMMA) (Plexiglas Film 0F058, thickness: 200 μm, provided by Evonik [Germany]) by the aid of a casting knife film applicator (Elcometer 3580/4, Elcometer Ltd., UK).…”

“…In this study, we used a perspiring skin simulator, which is described in detail elsewhere. 13 Briefly, the setup comprises a multilayer skinmimicking substrate, a chamber located underneath the substrate, a syringe pump, and connecting tubes, as illustrated in Figure 1. The ), and the three-layered structure (gelatin, PMMA substrate, and double-sided adhesive) was then laser-drilled to make funnel-like holes to mimic sweat pores.…”

Multilayer diffusion modeling and Coherent anti‐Stokes Raman scattering microscopy for spatially resolved water diffusion measurements in human skin

“…This could measure diffusion coefficients on the order of 10s of μm 2 /s, corresponding to typical values of cytoplasmic proteins [46]. The label free visualization of CARS microscopy would support measurement of a wide range of substances such as drugs and metabolites [34,35,47]. Interestingly, it was also found, that it was only possible to fit the data satisfactorily to the multilayer model, and not the one-and three-layer models.…”