Zinc oxide remains one of the best forms of sun protection thanks to its ability to block both UVB and UVA rays. However, few really appreciate its thick white look – except, maybe, lifeguards in the '80s. UCLA researchers believe they have a solution.
The chalky white cast that some sunscreens lend to skin is one of the reasons people tend to shy away from them. After all, when you're trying to show off that hard-won summer tan, the last thing you want is something that'll make you look like you spent the whole summer in your mom's basement. Yet, using sunscreens is one of the best ways to ward off the leading cause of preventable skin cancer.
So, if a sunscreen could be developed that kept its protective ability without making people look slightly vampiric, more people might use it. That's at least part of the thinking that led researchers at UCLA to come up with a solution.
“The best sunscreen is the one people will actually use,” said AJ Addae, first author of the study that describes the team's work. “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.”
In creating their new formulation, the researchers felt that they didn't necessarily need to create a brand new chemical formula, considering that zinc oxide (ZnO) has proven itself to be safe and well tolerated in sunscreens for years. So instead, they focused on changing the shape of the zinc oxide particles themselves.
The issue with current sunscreens is that the zinc oxide particles they contain are more or less round – like blood platelets – and tend to clump together. This causes them to scatter visible light, leading to the notorious white or gray cast, especially on darker skin tones.
So the UCLA team used a process called flame synthesis to change the shape of the particles.
This involved heating a material containing Zn²⁺ ions in 900°C (1,652°F) temperatures. This caused the Zn²⁺ particles to vaporize and break apart. As the particles were cooled, the free zinc bound with oxygen to form zinc oxide crystals. But more importantly, the ZnO crystals took on a tetrapod shape, meaning they had four legs radiating out from a central hub, sort of like jacks from the popular game. This unique shape kept them from clumping.
“Because of their structure, these tetrapod-shaped particles have standoffs and form porous networks instead of collapsing into clumps,” said Addae. “They can’t pack tightly and aggregate, so they stay evenly distributed in the sunscreen.”
The new sunscreen achieved an SPF rating of 30 and – without the clumping particles – was visibly less whiter, as confirmed by an array of color science metric tests the team conducted. Addae, who is Ghanaian-American, also saw an immediate difference when she applied it to her own skin.
“When I spread it on my own skin, I didn’t get that white cast I usually see with zinc oxide,” said Addae. “That was the moment I realized this could really work.”
In fact, Addae says part of the motivation to conduct the research was the way in which traditional sunscreens looked when she used them herself.
“I started thinking about this because I was frustrated by how mineral sunscreen looks on my own skin,” she says. “A lot of my motivation came from my own experience trying to use mineral sunscreen and dealing with the white cast and other unsightly aesthetic issues. This led me to simply avoid sunscreen altogether. That frustration really became the starting point for this work.”
Addae and her team are now working with UCLA Health's Skin of Color Clinic to sort out how the new ZnO particles affect the skin's microbiome as a first step toward making a commercially viable product.
The research detailing the team's work has been published in the journal, ACS Materials Letters.
Source: UCLA Health
