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Sunscreens made with mineral active ingredients, such as zinc oxide and titanium dioxide, generally score well in EWG’s Guide to Sunscreens because they provide strong sun protection with few health concerns and don’t break down readily in the sun. In fact, zinc oxide and titanium dioxide are the only two sunscreen ingredients categorized as safe and effective by the Food and Drug Administration in their proposed sunscreen regulations..
To create mineral-based sunscreens that are both usable and effective, manufacturers often use nano-size versions of these minerals – materials measured in nanometers, or billionths of a meter – to reduce white cast and increase SPF.
More research is needed to fully understand the extent to which nanoparticles may harm cells and organs if they’re introduced into our bodies. And though some studies have produced little evidence that zinc oxide and titanium dioxide nanoparticles can cross the skin in significant amounts, other research has shown that nanoparticles can still be absorbed through the skin and lead to toxic side effects in skin cells.
One real-world study tested the penetration of zinc oxide on human volunteers who applied sunscreens twice daily for five days but found less than 0.01 percent of zinc entering the bloodstream.
Other studies, including one by FDA scientists and another by researchers in Europe, concluded that neither zinc oxide nor titanium dioxide nanoparticles penetrate the skin. A 2018 study concluded that nano-titanium dioxide does not penetrate the skin beyond the surface layer, and a study by Italian researchers focused on the potential for nanoparticles to cross damaged skin and found no evidence it happens.
But it may be dangerous to inhale or ingest nanoparticles. The lungs have trouble clearing small particles, which may pass from the lungs into the bloodstream. If swallowed, nanoparticles can damage the gastrointestinal tract, though there is little evidence to suggest consumers swallow enough zinc oxide or titanium dioxide from sunscreen for this to pose a concern.
But the FDA is proposing additional tests for sunscreens in powder and aerosol form to ensure no nanoparticles or small particles are released that could damage the lungs.
Because of these inhalation concerns, EWG strongly discourages the use of loose powder makeup or spray sunscreens containing titanium dioxide or zinc oxide of any particle size.
The use of nanoparticles in cosmetics poses a regulatory challenge, because their properties may vary widely, depending on their size, shape, surface area and coatings. We don’t know everything we’d like to know about their performance, because manufacturers are not required to disclose the qualities of the particles used in their sunscreens.
Many companies sell products advertised as containing non-nano titanium dioxide and zinc oxide. These claims are misleading.
More research and more specific FDA guidelines are essential to reducing the risk and maximizing the sun protection of mineral sunscreens. FDA sunscreen rules allow any type of titanium dioxide or zinc oxide to be used in sunscreens. To ensure the safety and effectiveness of nanomaterials in sunscreen, the FDA should restrict forms of zinc and titanium that would provide inadequate UV protection or that could be activated by UV rays and damage skin cells. Yet even with these uncertainties, we believe zinc oxide and titanium dioxide lotions are among the best sunscreen choices on the U.S. market.
EWG’s favorable rating of mineral sunscreens is not an endorsement of nanomaterials in all consumer products. EWG has urged the FDA to carefully review the safety of nano-size particles in cosmetics products and to evaluate skin and lung penetration and the potential for greater toxicity to body organs. Consumers’ potential exposure to nanoparticles in sunscreens has been carefully studied and, unlike other consumer products with nanomaterials, sunscreens play an important role in UV protection.
EWG remains deeply concerned about the general lack of oversight of nanotechnology and associated risks to consumers, people with workplace exposures and the environment. Government regulators should exercise strong oversight to ensure that the production, use and disposal of nanomaterials does not harm workers and the environment.