The white cast that mineral sunscreen leaves on skin, especially darker complexions, has long been a reason people skip sun protection altogether. UCLA scientists say they have found a simple fix: reshape the zinc oxide particles that sit at the foundation of these products.
Researchers at the UCLA Health Jonsson Comprehensive Cancer Center engineered zinc oxide into microscopic structures called tetrapods, which look like tiny four-armed crosses. In testing, these reshaped particles delivered the same sun protection factor of 30 while producing far less visible residue and better stability in the formula over time.
The breakthrough matters beyond cosmetics. Skin cancer is the most common cancer in the United States, and ultraviolet radiation remains the leading preventable cause. Yet many people avoid regular sunscreen use because mineral formulas often leave them looking ghostly. The problem falls heaviest on people with darker skin tones, who already face disparities in skin cancer detection and outcomes.
"If improving how sunscreen looks leads to more consistent use, it could have real implications for skin cancer prevention," said Paul S. Weiss, the study's senior author and a UCLA chemistry and materials science professor.
The motivation for the work came from frustration. AJ Addae, a UCLA doctoral candidate in chemical biology, found that standard mineral sunscreen looked so obvious on his own skin that he often skipped applying it. That personal experience pushed him to explore whether the underlying materials themselves could be altered rather than adding pigments to hide the white cast.
Zinc oxide has been the workhorse ingredient in mineral sunscreen for good reason. The FDA recognizes it as safe and effective at blocking both UVA rays, which accelerate skin aging, and UVB rays that cause sunburn and increase cancer risk. Dermatologists often recommend mineral sunscreen for people with sensitive skin, acne, or rosacea, or those who prefer non-chemical options.
The problem lies in how the particles behave. Standard zinc oxide in sunscreen consists of tiny spherical nanoparticles made through conventional chemical processes. These particles tend to clump together, which makes the formula less stable and causes light to scatter visibly across the skin, creating that telltale grayish or white film.
The UCLA team used a different manufacturing approach: high-temperature flame synthesis that produces much larger particles shaped like tetrapods. Because of their geometry, these structures have small spacers built in. They cannot pack tightly or collapse into clumps the way spherical particles do. Instead, they stay evenly distributed throughout the sunscreen, forming loose networks.
"Because of their structure, these tetrapod-shaped particles have standoffs and form porous networks instead of collapsing into clumps," Addae explained. "They can't pack tightly and aggregate, so they stay evenly distributed in the sunscreen."
When researchers applied tetrapod-based sunscreen in controlled tests on skin, the results were striking. The formulation appeared warmer in tone and blended more closely with natural skin pigmentation. The intense white or gray cast vanished. Remarkably, no added pigments or special coatings were needed to achieve the effect.
The tetrapod sunscreens also proved more stable as time passed, showing fewer signs of separation or unusual thickening that can make products unpleasant to use.
"When I spread it on my own skin, I didn't get that white cast I usually see with zinc oxide," Addae said. "That was the moment I realized this could really work."
The findings, published in ACS Materials Letters, suggest that materials science could unlock a practical lever for skin cancer prevention. Melanoma is less common among people with darker skin tones, but when it does occur, survival rates lag significantly. One major factor is late-stage detection, often because people have not been screened or do not use preventive sun protection consistently.
Much work remains before this technology reaches store shelves. The researchers are now partnering with UCLA Health's dermatology department and Skin of Color Clinic to study how the tetrapod particles interact with the skin microbiome and to move the formula toward commercial viability.
"The best sunscreen is the one people will actually use," Addae said. "If zinc oxide can be made to look better on more skin tones without sacrificing protection, it could help more people protect themselves from the sun's most dangerous effects."
Author Jessica Williams: "This is the kind of elegant solution that happens when materials scientists listen to what actually stops people from protecting their health. Reshape a particle, change behavior, save lives."
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