Citation: Yuan Zeng, et al. (2023) Coral-friendly and non-transdermal polymeric UV filter via the Biginelli reaction for in vivo UV protection. Cell Reports Phys. Sci. Vol. 4 (3), 101308. ISSN 2666-3864. doi.org/10.1016/j.xcrp.2023.101308.
In Pursuit of a Safe Sunscreen
Small, Ultra Violet-sensitive molecules, called “UV filters”, are added to sunscreens as active ingredients. These molecules are what allows sunscreen to do its job, preventing sunburns on a day at the beach and protecting against skin cancer in the long-term. However the small size and low molecular weight (the mass of a molecule) of these molecules allows them to penetrate the skin. Once in the body, these molecules mimic certain hormones in the body and can potentially cause harm, though their effects are still being researched. Small-molecule UV filters can also harm the marine environment. They contribute to coral bleaching and disrupt the ability of algae to photosynthesize.
As knowledge about the harmful effects of small molecule UV filters has come to light, governments have been strengthening regulations on their use. For example, in 2021 Hawaii banned the sale and distribution of any sunscreen containing oxybenzone and avobenzone (two common small molecule UV filters). Some coral and body-safe alternatives exist, like mineral sunscreen, though researchers are working hard to develop new UV filters that will create safe sunscreens for both people and the environment. Researchers at Tsinghua University in Beijing recently conducted a study in which they developed and tested a new kind of UV filter that is both safe for humans and the environment.
The biggest problem of common active ingredients in sunscreen is the fact that these molecules are incredibly small and easily absorbed through tissues, so these researchers created a molecule with a higher molecular weight. This prevents the active ingredient from penetrating your skin or the tissue of a coral, which is a big first step in making it eco-friendly. They did this by using a common method in chemistry called the Biginelli reaction, which is usually used to make biologically-active compounds that we use everyday like anti-inflammatories, antimicrobials, and antioxidants. Until this study, no one had used this handy reaction for making sunscreen, but the researchers were able to successfully create a new kind of UV filter that outperforms both oxybenzone and avobenzone in tests on skin protection, and coral/algal health.
Testing the Product
The researchers first tested the ability of their new UV filter, called P3, against UV radiation. Afterall, when developing a new product, one wants to ensure that it does what it’s supposed to!
They tested the effectiveness of P3 by applying it on the skin of mice and exposing the mice to enough UV radiation to cause a mild sunburn. They compared the effectiveness of P3 against the typical compounds used in commercial sunscreens (oxybenzone and avobenzone) and a control (no sunscreen) and found that P3 provided better protection against UV radiation than traditional small molecule UV filters!
The researchers also tested how much each UV filter absorbed into skin. The biggest threat to human health caused by small molecule UV filters is that they get absorbed into the body and look like hormones, which can disrupt certain body processes. Their hypothesis was that the larger molecule UV filters won’t be absorbed by the skin due to their large size. This was tested on a line of epithelial cells (skin cells), by introducing the two small molecule filters and their new large molecule filter to the cell’s surface. Fluorescent tags were used to track the movement of the UV filters through the skin cells over 24 hours. They found that both oxybenzone and avobenzone penetrated through all layers of the skin while P3 stayed on the surface.
Next, they ran several environmental safety tests to compare the effects of P3, oxybenzone, and avobenzone on coral and algae. Current UV filters are a huge burden on the environment, and oxybenzone is the worst offender, contributing to both coral bleaching and distribution of photosynthesis in algae. They tested each compound on algae by culturing a common species, Chlorella, with each UV filter at concentrations typically found in the environment. After one week of exposure, they compared the cultures and found that the culture with oxybenzone was completely dead, while avobenzone and the new UV filter did not affect the algae.
They also exposed two common coral species, Acropora and Palythoa, with each UV filter at typical environmental concentrations for two weeks. The corals that were exposed to P3 and avobenzone retained their color and didn’t bleach, while oxybenzone caused bleaching by day 5 of the experiment.
Safer Sunscreen for a Healthier Planet
This study developed a new active ingredient for sunscreens which proved to be not only safe for both humans and the environment, but also equally or more effective than traditional UV filters. This encouraging news shows that environmentally safe products are being developed all over the world to address important issues like coral bleaching while improving human health. As you prepare for longer days and sunnier weather, be sure to do your research on Reef Safe Sunscreen and read the fine print on sunscreen labels to ensure what you’re buying is both eco-friendly and safe!
Cover Image: El Mirador beach, Cancun. From Wikivoyage.org by Luyten.
I am a masters student at the University of Rhode Island, studying the ecology of the harmful algal bloom genus, Pseudo-nitzschia. My work is interdisciplinary and revolves around coastal health, water quality, and public engagement with science. In my free time I enjoy doing crafts, writing, cooking, and exploring the outdoors on my feet or a pair of skis.