Photophysical Studies for Rational Sunscreen Design
Creators: name: University Of California Office Of The President
Publisher: name: University of California Office of the President
publisherIdentifier: https://ror.org/00dmfq477
publisherIdentifierScheme: ROR
Year: 2024

description: Sunscreens are recommended and widely used by Californians to prevent sunburn and consequently to reduce the risk of skin cancers and photodamage. Exposure to UV light causes adverse photobiological effects like sunburn, photoaging, and skin cancer. Sunscreens work by attenuating ultraviolet (UV) radiation (290 nm -400 nm) at the skin surface through the use of molecules known as UV filters. The ideal UV filter would be a stable molecule that absorbs UV radiation and releases the energy as heat without losing its ability to attenuate UV radiation. UV filters used in sunscreen products today possess two potentially undesirable characteristics. First, some of the UV filters may degrade chemically under UV exposure due to photochemical reactions. Even if these degradation reactions are very low yield, under intense solar radiation the capacity of the sunscreen to protect the skin may be reduced. The instability of these molecules under sustained light exposure is well known, and the Food and Drug Administration (FDA) list of approved UV filters contains molecules that are photolabile, leading to a loss in UV attenuation and subsequently a loss in efficacy of the sunscreen product. A second area of concern is the chemical activity of intact sunscreens that penetrate beneath skin’s surface. When UV light is present, solution phase studies have found that some UV filters have reactive long-lived (triplet) states that can generate reactive intermediates, including reactive oxygen species (ROS) like singlet oxygen. In vitro studies in our lab have recently shown that three widely used UVB filters sensitize ROS formation in cytoplasmic organelles in the epidermis. Both the loss in UV attenuation as well as increased formation of reactive intermediate states present serious public health issues as they place the sunscreen user at risk for skin damage due both to increased UV exposure at the skin surface and to unwanted chemical reactions in the nucleated epidermis. Clearly, there is much room to improve the efficiency and durability of UV filter performance. Through a trial and error approach, formulators have found that, by combining some UV filters, photostability can be increased so that loss in UV attenuation by UV filters is minimized. While progress is proceeding, clearly it would be desirable to speed up the development of new and improved sunscreen products, which could have a significant impact on public health. Given the importance of photostability in sustaining the efficacy of sunscreen products over entire periods of UV exposure, we propose collaboration with Merck (formerly Schering-Plough Healthcare Products, Inc.) Consumer Care’s Coppertone Solar Research Institute to identify the pathways of photoinstability of UV filters. Using time-resolved spectroscopic methods, the excited state reaction pathways for the most commonly used UV filters globally will be identified. A very limited amount of data is available in the