For decades, dermatological consensus has underscored the critical importance of consistent sunscreen use in minimizing exposure to harmful ultraviolet (UV) radiation, a primary modifiable risk factor for skin cancer, which stands as the most prevalent malignancy in the United States. Despite widespread awareness of these risks, a significant portion of the population fails to adhere to regular sunscreen application. A frequently cited impediment to consistent use, particularly with mineral-based sunscreens, is the conspicuous white or grayish cast left on the skin by their active ingredients, notably zinc oxide.
Addressing the inherent visual drawbacks of mineral sunscreens has been a long-standing challenge in dermatological and cosmetic science. A pioneering study spearheaded by researchers at the UCLA Health Jonsson Comprehensive Cancer Center proposes a solution that sidesteps the development of entirely new chemical compounds. Instead, the innovative approach focuses on fundamentally altering the physical architecture of the zinc oxide particles already integral to many mineral sunscreen formulations.
The research team meticulously designed zinc oxide into unique, microscopic four-armed structures, scientifically termed tetrapods. According to the researchers’ findings, these specially engineered particles exhibit a remarkable capacity to provide robust defense against damaging UV radiation while simultaneously generating a substantially less pronounced white cast compared to conventional zinc oxide formulations. The outcomes of this investigation, disseminated in the esteemed journal ACS Materials Letters, hold considerable promise for advancing skin cancer prevention efforts by enhancing the aesthetic appeal of mineral sunscreens, thereby encouraging more widespread and regular adoption across a diverse spectrum of skin tones.
Senior author of the study, Paul S. Weiss, who holds a distinguished UC Presidential Chair and serves as a professor across multiple disciplines at UCLA, including chemistry, biochemistry, bioengineering, and materials science and engineering, emphasized the broader implications of this development. Professor Weiss, also an investigator at the UCLA Health Jonsson Comprehensive Cancer Center, stated, "This endeavor transcends mere cosmetic improvement. The potential for this innovation to foster more consistent sunscreen usage, by making it more visually acceptable, could translate into tangible advancements in skin cancer prevention."
The potential advantages of this reformulated sunscreen are particularly pertinent for individuals with darker skin tones. This demographic often demonstrates lower rates of consistent sunscreen use and, consequently, faces a higher likelihood of being diagnosed with skin cancer at more advanced, challenging-to-treat stages. While melanoma, the most aggressive form of skin cancer, occurs with less frequency among individuals with darker complexions, available research indicates that they are disproportionately more likely to succumb to the disease. This disparity is often attributed to the later detection of melanoma, which complicates treatment efficacy.
For AJ Addae, the first author of the study and a doctoral candidate in chemical biology at UCLA with a background in cosmetic science entrepreneurship, the impetus for this research stemmed from personal experience. Addae articulated, "My initial engagement with this problem arose from my personal frustration with the visual appearance of mineral sunscreen on my own skin. A significant portion of my motivation was rooted in my own attempts to use mineral sunscreen and my dissatisfaction with the resultant white cast and other aesthetically unappealing characteristics. This led me to, at times, forgo sunscreen altogether. That feeling of frustration truly served as the genesis of this research."
The ubiquitous use of zinc oxide in mineral sunscreens is largely attributable to its efficacy in blocking both UVA rays, which are associated with skin aging, and UVB rays, which are responsible for sunburn and elevate the risk of skin cancer. The U.S. Food and Drug Administration has affirmed the safety and effectiveness of zinc oxide as a sunscreen agent. Mineral sunscreens are frequently recommended for individuals with sensitive skin, those prone to acne, individuals managing rosacea, or people who simply prefer formulations that do not rely on chemical UV filters.
However, the inherent nature of standard zinc oxide particles often leads them to aggregate, forming clumps. This tendency can compromise the stability of sunscreen formulations and cause the particles to scatter visible light, resulting in the characteristic white or gray residue that is particularly noticeable on darker skin tones. The research team at UCLA embarked on an investigation to determine whether modifications to the physical structure of these particles could preempt such clumping and consequently enhance the cosmetic appeal of the sunscreen.
The vast majority of zinc oxide employed in sunscreens comprises extremely small, roughly spherical nanoparticles, typically produced through standard chemical manufacturing processes. In contrast, for their groundbreaking study, the UCLA researchers utilized significantly larger particles fabricated via a proprietary high-temperature flame process. These meticulously crafted particles possess a distinct tetrapod morphology. Addae explained, "Due to their inherent structure, these tetrapod-shaped particles feature protruding arms, which act as structural supports, and consequently form porous networks rather than collapsing into dense clumps. Their inability to pack tightly and aggregate ensures their uniform distribution throughout the sunscreen base."
The comparative analysis conducted by the researchers pitted the tetrapod-shaped zinc oxide against conventional zinc oxide nanoparticles commonly found in mineral sunscreens. The formulations incorporating the tetrapod particles yielded a spectrum of practical advantages. When both types of zinc oxide were incorporated at equivalent concentrations, the sunscreen utilizing tetrapods achieved a sun protection factor (SPF) of approximately 30, a level of efficacy comparable to that offered by standard mineral sunscreens. Furthermore, the lotions formulated with tetrapods exhibited superior stability over time, displaying fewer indications of phase separation or undesirable thickening.
The most visually striking improvement was observed in how the tetrapod particles interacted with visible light. Through a series of controlled laboratory experiments and subsequent applications on human skin, the tetrapod sunscreen presented a warmer, more natural appearance that closely harmonized with diverse skin tones. Crucially, it did not produce the intense white or gray cast that is a hallmark of conventional zinc oxide formulations. This aesthetic enhancement was achieved without the incorporation of additional pigments or specialized coatings designed to mask the residue. Addae recounted his personal revelation, stating, "When I applied it to my own skin, I did not observe the white cast that I typically associate with zinc oxide. That was the precise moment I realized the profound potential of this innovation." Weiss, who is also affiliated with the California NanoSystems Institute at UCLA and the UCLA Goodman-Luskin Microbiome Center, added, "What was particularly surprising to us was the rapidity with which the improvements became apparent. Even the very initial formulations demonstrated a discernible difference in appearance."
While the commercial availability of this advanced sunscreen technology will necessitate further rigorous testing and regulatory approvals, the researchers assert that their findings powerfully illustrate how innovations in materials science can effectively address practical barriers to widespread skin cancer prevention. Addae reiterated the core principle of their work, stating, "The most effective sunscreen is ultimately the one that individuals will consistently use. If zinc oxide can be engineered to offer a more aesthetically pleasing appearance across a wider range of skin tones, without compromising its protective capabilities, it could empower more people to shield themselves from the sun’s most detrimental effects." The research team is currently engaged in collaborative efforts with the UCLA Health department of dermatology, including specialists at UCLA Health’s Skin of Color Clinic. Their ongoing work aims to investigate the interaction of the tetrapod particles with the skin microbiome and to further advance the development of practical, real-world applications for this groundbreaking technology. The study’s co-authors include Jennifer Uyanga and Addae’s thesis co-advisor, Professor Justin Carman of UCLA Chemistry, alongside Professor Yogendra Kumar Mishra from the University of Southern Denmark. This research was made possible, in part, through funding from the National Science Foundation, the Challenge Initiative at UCLA, and a Sigma Xi IFoRE Grant-in-Aid.
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