One of the key concerns for sun care products is that their active ingredients should not penetrate into the skin: sunscreens are designed to stay on the surface or within the outermost skin layers. Verifying whether this actually happens requires reliable analytical tools, and this is where Raman spectroscopy plays a role, enabling researchers to detect and quantify the penetration of UV filters and other sunscreen active ingredients.
Sometimes you want to show that a topically applied product does not penetrate the skin. For example, UV filters do their work on the skin and in the top part of the stratum corneum: they are not supposed to penetrate. This would affect their UV protection effectiveness. Moreover, endocrine system disruption by UV filters that become systemically available is a major health concern.
A research group from Guangzhou published an interesting paper titled “A combined study of skin penetration by confocal Raman spectroscopy and human metabolism: A case of benzophenone-3 in sunscreen” (Wang M, Tan J, Qi Z, Ge X, Li G, Yu Y., 2024). They used the gen2-SCA Skin Composition Analyzer to measure the skin penetration of benzophenone-3 (BP3), a UV filter that has been widely used for over 30 years, because of its high UV-absorption efficiency and good light stability.
Benzophenone-3 is used in numerous personal care products. Studies found BP3 in serum, placental tissue, breast milk, urine, amniotic fluid, hair and nails. This has raised concerns because BP3 has been shown to be “an endocrine disruptor that interferes with growth and development in humans and animals” (Kunisue et al., 2012; Schlumpf et al., 2001; Zhang et al., 2013).
The researchers applied a sunscreen formulation containing 5.72% BP3 under real, whole-body exposure conditions, combining confocal Raman measurements of the skin with urinary monitoring of BP3 and its metabolites over time, the “combined” approach the paper’s title refers to.
Using this combined approach, they were able to track BP3 both at the skin surface and inside the body over time. This gave a much more complete picture of the full journey of this UV filter inside the body, from the topical application on the skin to complete systemic clearance.
Some important conclusions from the paper are that:
It is undoubtedly fundamental to further investigate the penetration and the behaviour of these chemicals, such as BP3.
Benzophenone-3 skin absorption has been studied by in vivo and in vitro methods. In vitro methods, such as diffusion-cell experiments and tape-stripping, require complex procedures to quantify BP3 and do not provide a clear picture of how it is distributed within the tissue. On the other hand, most in vivo results are obtained in animal studies, but animal skin is different from human skin.
Confocal Raman spectroscopy represents an effective and trustworthy approach for exploring the penetration of Benzophenone-3 into the human stratum corneum in vivo. By enabling non-invasive, in vivo measurements, it provides detailed insight into how compounds used in topical products distribute in the skin.
Analysis of the gen2-SCA results by SkinTools, RiverD’s data analysis software, yields fully quantitative analysis of skin penetration of topically applied products (concentrations in mg/cm3; total product uptake in µg/cm2). It is a powerful tool to assess the skin penetration of UV filters and to compare the impact of different formulations.
Read the full publication here: https://www.sciencedirect.com/science/article/abs/pii/S0269749123018705
