Mineral sunscreens, while favored by many for their skin-friendly approach to UV protection, have long been criticized for leaving a noticeable white cast on the skin. A new study published in ACS Materials Letters reveals a potential solution: reshaping zinc oxide nanoparticles into a four-armed “tetrapod” structure. This innovation not only improves the aesthetic experience of mineral sunscreen but also addresses stability issues that have plagued formulations in the past.
The Problem with Traditional Mineral Sunscreens
Zinc oxide, the active ingredient in mineral sunscreens, effectively blocks harmful ultraviolet (UV) radiation, a leading preventable cause of skin cancer. Unlike chemical sunscreens, which absorb into the skin, mineral formulas sit on top of the skin, offering a physical barrier. However, the chalky nature of zinc oxide can clump together in suspension, creating visible streaks and an undesirable white appearance. This is a major reason why many people, particularly those with darker skin tones, avoid mineral sunscreens altogether.
Beyond aesthetics, these clumps also reduce shelf life and make it harder for manufacturers to guarantee consistent performance. Chemical sunscreens, though they have other considerations, are easier to stabilize.
The Tetrapod Solution
Researchers at UCLA, led by doctoral candidate Ajoa Addae, found that altering the shape of zinc oxide nanoparticles could mitigate these issues. Using a process called “flame synthesis,” they created tetrapod-shaped particles – four-armed structures that resist clumping.
“Because of their structure, these tetrapod-shaped particles have standoffs and form porous networks instead of collapsing into clumps,” Addae explains. This prevents the formation of visible streaks and ensures even distribution within the sunscreen.
Performance and Stability
Critically, the new shape does not compromise UV protection. The tetrapod formulation achieved a Sun Protection Factor (SPF) of 30, the standard for mineral sunscreens, effectively blocking both UVA and UVB rays. Moreover, stability testing demonstrated that the new mixture is less prone to separation or thickening over time compared to traditional spherical particles. This means longer-lasting performance for consumers.
A Focus on User Experience
The research was driven by real-world concerns. Addae herself struggled with the white cast and aesthetic issues of mineral sunscreens, motivating the study. The tetrapod structure scatters visible light differently, creating a warmer tone more acceptable to a wider range of skin tones.
“When I spread it on my own skin, I didn’t get that white cast I usually see with zinc oxide,” Addae stated. “That was the moment I realized this could really work.”
Future Steps
While promising, the tetrapod nanoparticles still require thorough human and environmental safety testing before widespread adoption. Scaling up production in a cost-effective manner is also a key challenge. However, industry experts like Kyra Sedransk Campbell, CEO of Kingston Street Consulting, see significant potential.
The application-driven focus of this research is “really exciting” and has the potential to translate into real impact.
This innovation could reshape the market for mineral sunscreens, making them more accessible and appealing to a broader consumer base while maintaining effective UV protection.
