While the importance of wearing sunscreen is often emphasized, rarely do we stop to consider how sunscreen works and why it is effective. A thorough understanding of these details is essential for dermatologists and trainees alike to feel confident navigating conversations with patients about sunscreen formulations, efficacy, and safety. At the inaugural Lab to Label Conference, Dr. Candrice Heath, MD, a triple board-certified dermatologist and associate professor of dermatology at Howard University, and Dr. Joshua Williams, PhD, Manager, Fellow, Sun and Hair Care Global Translational Science Lead at Kenvue, joined forces to shed light on the science behind ultraviolet (UV) filter ingredients and how they power current sunscreen products. Key points from their talk are summarized below.
The Solar Spectrum
Dr. Heath and Dr. Williams began the discussion with a brief overview of the solar spectrum. They reminded us that various proportions of different wavelengths of radiation energy reach the Earth; UVA (320-400 nm) makes up 9.5% of these wavelengths, and UVB (290-320 nm) comprises only 0.5%. Despite making up such a small percentage, UVB is more energetic, meaning it reacts faster and causes more damage, in the form of burning and skin cancer. On the other hand, UVA is less energetic, reacts more slowly, penetrates deeper into the skin, and is associated with tanning, aging, and freckling.
Chemical vs. Mineral UV Filters
Next, the speakers discussed UV filters – the active ingredients in sunscreens that absorb, reflect, and/or scatter UV rays. The primary UV filters are comprised of mineral/inorganic filters (i.e., zinc oxide, titanium dioxide) and chemical/organic UV filters (i.e., octocrylene, avobenzone, octisalate, homosalate, ensulizole). These filters differ greatly in their formulation requirements to achieve a similar mechanism of action. In terms of formulation, chemical sunscreens are comprised of organic filters dissolved into a solvent, whereas mineral sunscreens are comprised of microcrystal, inorganic filters that are suspended in a formulation. Nonetheless, an essential aspect of formulating both chemical and mineral sunscreens is maintaining a stable emulsion to prevent separation of UV filters. Without this stability, the product cannot form an even film of the active ingredients on the skin, compromising efficacy. Regarding their mechanisms of action, both types of filters absorb UV rays, but depending on the exact physical properties, mineral filters may also reflect and scatter some wavelengths of light. Despite these differences in formulation and function, both mineral and chemical sunscreens provide safe and effective sun protection.
Photostability
Dr. Williams further elaborated on the importance of formulating photostable sunscreens. When sunscreens are not well formulated, they can break down and lose efficacy. Avobenzone is the primary UVA filter ingredient in the United States, however, it is naturally unstable when exposed to UV rays. Dr. Williams shared that Neutrogena developed Helioplexâ technology, which refers to a set of solutions with different chemical formulas that stabilize this key UV filter ingredient and the corresponding UVA protection that it provides. Key components of these formulas include additional UV filters – octocrylene, for example, stabilizes and works synergistically with avobenzone, collectively providing effective UVA and UVB protection.
Evidence and Regulation
In this discussion, Dr. Williams and Dr. Heath highlighted the ample available evidence demonstrating the skin health benefits of sunscreen. Several studies have shown that sunscreen prevents DNA damage, sunburn cell formation, upregulation of inflammatory markers, and immune suppression. Given the classification of sunscreen as a drug to prevent sunburn and skin cancer, and the strict regulation of drugs by the FDA, we can feel confident in the scientific evidence supporting sunscreen’s efficacy. Dr. Williams further highlighted that sunscreens are, in fact, the only product with a cancer risk reduction claim when used as directed, along with other sun protection measures.
Sun Protection Factor (SPF) and UVA Protection
Next, the speakers outlined the fundamentals of sunscreen testing. To make an SPF claim, sunscreens must undergo clinical testing. The predominant method of testing, recognized by regulatory bodies across the globe, involves carefully measuring and applying sunscreen on the backs of subjects and inducing sunburn. Then, the SPF value is determined by calculating the ratio of the amount of energy required to produce sunburn on skin protected with sunscreen vs. unprotected skin. It is also important to have UVA protection that is commensurate with the SPF level as indicated on FDA-regulated sunscreens as Broad Spectrum. UVA protection may be measured by both in vitro, as required by the FDA, as well as in vivo testing. As UVA rays cause skin pigmentation, UVA protection may be assessed clinically by comparing the amount of energy required to induce pigmentation on skin treated with sunscreen vs. untreated skin.
Debunking Misconceptions
Before concluding, Dr. Williams and Dr. Heath addressed some common sunscreen misconceptions. Contrary to what many believe, sunscreen does not need to penetrate or be absorbed by the skin to be effective; it functions on the skin surface. Common guidance regarding applying sunscreen around 15 minutes before going outdoors is more about compliance and consistency with the way sunscreen efficacy is tested, not activation or efficacy. Additionally, they clarified that sunscreens do not wear “out” over time; rather, they wear “off” due to factors such as towel drying, sweat, rubbing areas such as your face, or friction from clothing or backpacks.
Final Thoughts
Dr. Heath and Dr. Williams delivered an insightful talk that thoroughly covered the essentials of UV filters as the key components of sunscreen products – from their formulation to their testing and regulation. Most importantly, they shared practical pearls about UV filter chemistry and differences among various filter types, enabling dermatologists to better educate their patients. While this scientific background is critical, they emphasized that it only translates into benefits if individuals consistently use sunscreens. Aesthetic factors, especially the whitening effect of mineral sunscreens, are also important to consider because they can deter regular use. Fortunately, ongoing research is focused on developing mineral sunscreens with reduced whitening to better accommodate diverse skin tones, which can ultimately improve patient adherence and optimize the protective benefits of sunscreen.
About the author
Nikita Menta, BA is a Medical Student at The George Washington University School of Medicine and Health Sciences.
