By Suherman Candra Maholtra 
In a significant advancement for dermatological science and public health, researchers at the University of California, Los Angeles (UCLA) have developed a novel mineral sunscreen formulation that addresses one of the primary barriers to consistent sun protection: the unsightly, chalky residue known as "white cast." By re-engineering the physical structure of zinc oxide particles, the team has created a formula that maintains high-level ultraviolet (UV) protection while remaining virtually invisible on a diverse range of skin tones. The study, published in the journal ACS Materials Letters, suggests that this innovation could play a pivotal role in reducing skin cancer rates by increasing consumer compliance, particularly among populations with darker skin who have historically been underserved by traditional mineral sunscreen products.
The Public Health Challenge: Skin Cancer and Sunscreen Non-Compliance
Skin cancer remains the most prevalent form of malignancy in the United States, with approximately 9,500 people diagnosed every day. While the vast majority of these cases are preventable through the consistent application of sunscreen and the reduction of ultraviolet radiation exposure, public health officials have long struggled with low rates of daily usage. According to data from the Centers for Disease Control and Prevention (CDC), less than 15% of men and 30% of women regularly apply sunscreen to their faces and other exposed skin when outdoors for more than an hour.
Dermatologists categorize sunscreens into two primary types: chemical and mineral (physical). Chemical sunscreens utilize ingredients like avobenzone or oxybenzone to absorb UV rays and convert them into heat. Mineral sunscreens, conversely, rely on inorganic minerals—primarily zinc oxide and titanium dioxide—to reflect and scatter UV radiation away from the skin. While mineral sunscreens are frequently recommended for individuals with sensitive skin, children, and those concerned about the systemic absorption of chemical filters, they are notorious for their aesthetic drawbacks. The "white cast"—a pale, ghostly film left on the skin—is a result of the mineral particles scattering visible light. This effect is particularly pronounced and often socially stigmatizing for individuals with deeper skin tones, leading many to forgo sun protection entirely.
The Innovation: From Spheres to Tetrapods
The research led by the UCLA Health Jonsson Comprehensive Cancer Center represents a departure from traditional cosmetic chemistry. Rather than searching for a new chemical UV filter—a process that can take decades and require extensive FDA approval—the team focused on the materials science of existing, safe ingredients.
Traditional mineral sunscreens utilize zinc oxide nanoparticles that are roughly spherical. Because of their shape and surface chemistry, these particles tend to aggregate or "clump" together within the sunscreen emulsion. When these clumps form, they become large enough to scatter visible light, which creates the opaque white appearance on the skin’s surface.
The UCLA team, spearheaded by AJ Addae, a chemical biology doctoral candidate, and Paul S. Weiss, a distinguished professor of chemistry and biochemistry, utilized a patented high-temperature flame process to create zinc oxide in the shape of microscopic tetrapods. These structures feature four protruding "arms" or spikes. This unique geometry prevents the particles from packing tightly together.
"Because of their structure, these tetrapod-shaped particles have standoffs and form porous networks instead of collapsing into clumps," explained Addae. "They can’t pack tightly and aggregate, so they stay evenly distributed in the sunscreen."
By maintaining a uniform distribution and preventing the formation of large aggregates, the tetrapod particles interact with light differently than spherical particles. They continue to provide a robust barrier against UVA and UVB radiation but allow more visible light to pass through or be absorbed by the skin, thereby eliminating the chalky residue.
Chronology of the Research and Personal Motivation
The genesis of this study was rooted in both scientific inquiry and personal experience. AJ Addae, who is also a cosmetic science entrepreneur, noted that her own frustration with available products served as the primary catalyst for the research. For many people of color, the choice has often been between a product that leaves a conspicuous gray film or no protection at all.
The research progressed through several critical phases:
- Synthesis and Characterization: The team utilized a high-temperature flame synthesis method to produce the zinc oxide tetrapods, ensuring the structures were uniform and scalable.
- Formulation Development: The researchers integrated these tetrapods into standard lotion bases, comparing them against control formulas containing conventional spherical zinc oxide.
- Stability Testing: The formulas were monitored over time to ensure that the tetrapods did not settle or separate, a common issue in mineral sunscreen manufacturing.
- Optical and SPF Analysis: Using both laboratory instrumentation and controlled skin applications, the team measured the Sun Protection Factor (SPF) and the "L-value" (a measure of lightness or whiteness) to quantify the reduction in white cast.
The results were immediate and striking. The very first formulations produced a visible difference, offering a warmer, more natural finish that blended into the skin without the need for added pigments or "tints" which are often used by brands to mask the whiteness of zinc oxide.
Supporting Data: Protection Without Compromise
A critical concern in sunscreen innovation is ensuring that aesthetic improvements do not come at the cost of efficacy. The UCLA study confirmed that the tetrapod-shaped zinc oxide is as effective as its traditional counterparts.
Key findings from the data include:
- SPF Parity: When used at identical concentrations, both the tetrapod and spherical zinc oxide formulas achieved an SPF of approximately 30. This level of protection meets the standard recommendation by the American Academy of Dermatology for daily use.
- Broad-Spectrum Coverage: The tetrapod structures effectively blocked both UVB rays (responsible for sunburn) and UVA rays (responsible for premature aging and long-term DNA damage).
- Enhanced Stability: The tetrapod lotions demonstrated superior structural stability. While traditional mineral sunscreens often thicken or separate over time due to particle clumping, the tetrapod network maintained a consistent viscosity, which is essential for shelf-life and ease of application.
- Reduced Light Scattering: Optical measurements confirmed that the tetrapod structures significantly reduced the scattering of visible light, confirming the subjective observations of a reduced white cast.
Addressing Health Disparities in Dermatology
The implications of this research extend far beyond the cosmetics industry; they address a critical gap in preventative healthcare. While the incidence of melanoma is lower in Black, Hispanic, and Asian populations compared to white populations, the mortality rates for these groups are disproportionately high.
Research indicates that Black patients are more likely to be diagnosed with melanoma at an advanced stage, when the five-year survival rate drops significantly. One contributing factor is a lack of awareness and a lower rate of sunscreen use, often driven by the fact that many products on the market were not designed with darker skin tones in mind.
"This isn’t just about cosmetics," said senior author Paul S. Weiss. "If improving how sunscreen looks leads to more consistent use, it could have real implications for skin cancer prevention."
By creating a "universal" mineral sunscreen that performs well on all skin tones, the UCLA team is providing a tool that can help bridge the gap in skin cancer outcomes. The researchers are currently collaborating with the UCLA Health Skin of Color Clinic to further validate the formula’s performance and appeal among diverse patient populations.
Future Outlook and Commercial Potential
While the laboratory results are promising, the journey from a university lab to a consumer product involves several more steps. The researchers are now focused on examining how the tetrapod particles interact with the skin microbiome—the community of beneficial bacteria that live on the skin’s surface. Preliminary plans are also in place to explore the environmental impact of the tetrapods, although zinc oxide is already widely considered "reef-safe" compared to certain chemical filters that have been banned in regions like Hawaii and the Virgin Islands.
The technology is currently protected by patents, and the team is exploring pathways for commercialization. Given the multi-billion dollar size of the global sunscreen market and the increasing consumer demand for "clean" and mineral-based products, a zinc oxide formula that eliminates the white cast is expected to see high demand from major skincare brands.
Conclusion: The Intersection of Materials Science and Medicine
The UCLA study serves as a prime example of how materials science can solve long-standing biological and behavioral challenges. By viewing the "white cast" problem as a physical hurdle involving light scattering and particle geometry rather than a chemical one, the researchers have unlocked a potential solution that uses already-approved, safe ingredients.
As the team continues their work with the UCLA Health department of dermatology, the focus remains on the ultimate goal: saving lives through better design. "The best sunscreen is the one people will actually use," AJ Addae noted. By making mineral sunscreens more aesthetically pleasing and inclusive, this research moves the medical community one step closer to a future where skin cancer prevention is accessible and acceptable for everyone, regardless of skin tone.
The study received support from the National Science Foundation, the Challenge Initiative at UCLA, and a Sigma Xi IFoRE Grant-in-Aid. Other contributors included researchers from the University of Southern Denmark, highlighting the international interest in this structural approach to sun protection.
