Sunburns hurt. And while they are most commonly associated with outdoor activities in the spring and summer, these painful red burns can occur any time of year – even when it’s cloudy. They arise from exposure to ultraviolet (UV) radiation from the Sun. This high energy light can damage the DNA in skin cells, leading to the formation of skin cancers. This risk increases with the frequency of exposure to UV light.
While melanin, the compound the body makes in response to UV exposure, does help by absorbing subsequent UV exposure and giving a great tan, it alone isn’t enough to prevent melanoma. Both the American Cancer Society1 and the American Academy of Dermatology2 recommend frequently wearing sunscreen as a part of a daily regimen to lower the risk of sunburns and skin cancer, and many products on the market do a fantastic job protecting consumers when they hit the beach, lake or hiking trail.
How Sunscreens Work
Broad spectrum sunscreens work alongside melanin by reflecting or absorbing UV radiation before it can damage DNA. The active ingredients in sunscreen fall into two major categories: mineral – metal oxides like zinc oxide – and organic – carbon-based molecules. Organic “filters” tend to possess common structures – such as derivatives of benzophenone, shown in Figure 1 – to absorb harmful UV rays and release them as heat or less dangerous wavelengths of light. Different structures do better jobs at absorbing different UV wavelengths, so sunscreens often blend them together to provide widespread coverage, and many have been used for decades.
However, there is increasing concern that some active ingredients utilized in sunscreen are damaging coral reefs and sea life.3,4 Some are appearing in the bloodstream at higher levels than previously thought, potentially opening up risks to human health.5 As a result, there is growing pressure to explore alternative sunscreen ingredients to ensure safe, effective and sustainable methods to protect skin. In silico methods can help R&D teams identify and characterize new UV filter candidates for future study in the lab more quickly, getting novel products to market – and protecting the environment – faster.
Predicting Optical Properties
The process of identifying any new sunscreen ingredient must start with a thorough understanding of its optical properties. We can use experimental methods like UV-Vis spectroscopy to quantitatively measure UV absorbance. However, preparing and running large numbers of samples can be labor intensive. Additionally, exploratory R&D into a novel chemical space can be expensive. As a result, research teams should start with in silico methods to quickly assess potential candidates in a relatively low resource environment.
For example, the VAMP module in BIOVIA Materials Studio provides a rapid, semi-empirical determination of UV-Vis absorption spectra for organic, inorganic and organometallic molecules based on their structure (see Figure 2). This allows researchers to explore large regions of chemical space to identify promising new compounds for further study. They can also run more targeted screens, selecting libraries of molecules already determined to be environmentally friendly to marine life. Armed with this initial knowledge, scientists can pass along these compounds for more testing, whether via other virtual methods like time-dependent density functional theory for more refined analysis of their optical properties or testing at the lab bench.
Determining Degradation Products
Another area to consider is the stability of the UV filters. Swimming in the ocean can expose the sunscreen to a relatively reactive environment: the ocean. Even many freshwater sources like lakes, rivers and swimming pools contain relatively high levels of dissolved salts and other compounds. This, coupled with irradiation by UV light, can result in the UV filter degrading over time into potentially hazardous products. To prevent this, “at risk” UV filters are coupled with other additives; for example, the common UVA filter avobenzone is stabilized with the addition of octocrylene, another UV filter6. However, effectively protecting UV filters does require an understanding of their breakdown products and their reaction mechanisms under different conditions.
Fukui function analysis, available in the DMol3 module of BIOVIA Materials Studio, can help researchers identify the susceptibility of a given atom in a molecule to electrophilic, nucleophilic or radical “attack.” This information can shed light on how a molecule might respond to different reaction conditions, such as in high UV or in the presence of oxidating agents like H2O2 or NaOCl. 7,8 These virtual insights can provide context to physical experimental results and lay a foundation for strategies to ensure long-term stability of sunscreen ingredients when in use and in the environment.
Towards Holistic Design of Personal Care Products
Designing sustainable sunscreens and other personal care products requires thorough consideration of the impacts of their constituent parts throughout the product lifecycle. In some cases, fundamentally different approaches may achieve a result that balances performance and safety. Scientists must now expand the criteria for what makes a good UV filter, not just its optical properties. Thankfully, research teams have a host of methods available to them to tackle these issues, and in silico techniques are quickly gaining support in driving holistic R&D initiatives.
The BIOVIA portfolio provides a comprehensive collection of solutions to help guide personal care R&D. The Materials Studio Collection for BIOVIA Pipeline Pilot can help expert computational chemists create and share sophisticated workflows with their colleagues at the bench, fostering collaboration and democratizing the power of these models. BIOVIA Solvation Chemistry, which utilizes the COSMO-RS methodology, can also shed light on the thermodynamic properties of UV filters in different solvents, providing much-needed context on how they will behave in the bottle, on the skin or in the water.
Creating successful and sustainable sunscreen ingredients requires considering a range of different molecular level properties. Part two of this blog series will explore the prediction of skin permeability of different sunscreen components to ensure effective and safe use.