Department of Chemistry, Technical University of Denmark, Lyngby, Denmark.
Riemann A/S, Hillerød, Denmark.
Int J Cosmet Sci. 2021 Jun;43(3):359-371. doi: 10.1111/ics.12703. Epub 2021 Jun 9.
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.
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 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.
防晒霜在出汗时保持对紫外线（UV）保护的能力对于其实际功效非常重要。然而，由于与水阻力和机械磨损相比，评估防晒霜持久性的相关协议相对较少，因此在防晒霜持久性评估中，这个问题很大程度上被忽视了。
为了更好地了解防晒霜在接触汗液时的行为，我们开发了一种出汗皮肤模拟器，其中包含一个模仿出汗人体皮肤的基底表面。我们使用这种出汗皮肤模拟器，通过体外防晒因子（SPF）测量、光学显微镜、紫外线（UV）反射成像和相干反斯托克斯拉曼散射（CARS）显微镜来评估防晒霜在出汗时的性能。
结果表明，出汗通过两种机制降低了防晒霜的效率，即防晒霜的洗去（影响薄膜厚度）和防晒霜的再分配（影响薄膜的均匀性）。此外，我们研究了出汗率如何影响这些机制，以及防晒霜的应用剂量如何影响出汗时的 UV 保护。正如预期的那样，较高的出汗率导致大量的 UV 保护丧失，而较大的应用剂量导致更多的防晒霜被洗去和再分配，但也在出汗前后提供了更高的 UV 保护。
