Scientists Test the Safety of a Key Sunscreen Ingredient on Skin Cells

Don't DIY your sunscreen just yet.

Unsplash / Matheus Vinicius

As the school year approaches and families head out for one last summer beach vacation, scientists announced a piece of comforting news: New research in the journal Biomicrofludics shows that titanium dioxide, one of the ingredients in sunscreen that’s attracted a lot of attention from health-conscious consumers, is safe to use.

In February, the US Food and Drug Administration proposed a new rule, calling for additional testing on a dozen ingredients commonly found in sunscreens, including oxybenzone, which is getting a lot of negative press over its potentially damaging effects on coral reefs. However, the FDA clarified that these 12 ingredients are not necessarily harmful to people, just that the agency is “seeking more data.”

In the wake of this FDA report and a much publicized study in the Journal of the American Medical Association that showed small amounts of sunscreen ingredients are absorbed into the bloodstream, some concerned people began opting to use do-it-yourself sunscreens made from essential oils. But as Inverse previously reported, “natural” sunscreens aren’t as carefully regulated as commercial sunscreens, and there’s not enough research to show that they offer any UV ray protection.

Many consumers are concerned about the ingredients in their sunscreen, but titanium dioxide is probably safe.

Unsplash / Maciej Serafinowicz

“I think that is scary; I don’t think that has any testing or any science behind it,” Doris Day, M.D., a dermatologist and associate professor at NYU Langone Medical Center previously told Inverse.

One of the chemicals cleared by the FDA’s February report, however, was titanium dioxide. Titanium dioxide has been under scrutiny in scientific literature, especially when it’s in a really tiny form called nanoparticles. In a scientific review published in October 2011 in the journal Nanotechnology Science and Applications, researchers concluded that titanium dioxide nanoparticles are not as effective at blocking UV radiation as larger particles. And perhaps more concerning, they observed that the nanoparticles can seep into layers of the skin.

But a study published Tuesday in Biomicrofludics confirms that titanium dioxide is not toxic to skin cells in small amounts. In the study, the scientists from the University of South Australia’s Future Industries Institute showed that titanium dioxide nanoparticles do not harm human skin cells and even protect cells against ultraviolet damage.

Dermatologists still say sunscreen is a must for a day at the beach, and a new study provides more evidence that sunscreen is safe.

Unsplash / Marvin Meyer

In the study, the researchers write that nanoparticles may be more or less toxic than larger amounts of the same material because their size can allow them to penetrate layers of your skin and potentially interact with your body’s systems.

“The general concern with nanoparticles is that size matters; how big an object is can determine where it goes and what it does,” Craig Priest, Ph.D., the senior author on the study and an associate research professor at University of South Australia, tells Inverse in an email. “Your pet cat can freely get into the house through the cat flap. A lion can’t, even though it is really just a big cat.”

Priest also says other concerns around nanoparticles include their shape and how they interact chemically with their environment — for example, with sunlight, sweat, and skin oils.

In order to test multiple toxic parameters at once and mimic real biological conditions, the researchers devised a method using a microfluidic device, which has extremely thin channels that allow the researchers to study titanium dioxide as nanoparticles and how those nanoparticles interact directly with skin cells.

When the scientists exposed skin cells to UV radiation alone, most of the cells died as the amount of radiation increased. However, very few cells died when exposed to titanium dioxide alone.

When exposed to a low level of UV radiation and increasing concentrations of titanium dioxide, more cells survived as titanium dioxide concentrations rose.

When exposed to an increasing amount of titanium dioxide, cells were more likely to survive UV radiation. The gray bars in this graph represent skin cells not exposed to UV radiation, and the pink bars represent cells exposed to UV radiation.

Biomicrofluidics/American Institute of Physics Publishing

“This is one of several exciting ways that miniaturization of fluidic systems can make a positive impact in industry and society,” Priest says. “If this method can streamline the development and use of nanoparticles in a safe way, that’s good for all of us.”

In the sunscreen debate, however, this study doesn’t answer many questions about the FDA’s 12 chemicals under scrutiny. The agency noted that titanium dioxide is “generally recognized as safe and effective.”

However, the study may pave the way for researchers to test more of the chemicals in sunscreen on a nanoparticle level to see how these molecules individually interact with skin cells under UV stress.

Abstract: Microfluidic screening is gaining attention as an efficient method for evaluating nanomaterial toxicity. Here, we consider a multiparameter treatment where nanomaterials interact with cells in the presence of a secondary exposure (UV radiation). The microfluidic device contains channels that permit immobilization of HaCaT cells (human skin cell line), delivery of titanium dioxide nanoparticles (TNPs), and exposure to a known dose of UV radiation. The effect of single-parameter exposures (UV or TNP) was first studied as a benchmark, and then multiparameter toxicity (UV and TNP) at different concentrations was explored. The results demonstrate a concentration-dependent protective effect of TNP when exposed to UV irradiation.
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