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Sunscreens made with the minerals zinc oxide and titanium dioxide generally score well in EWG’s ratings, because they provide strong sun protection with few health concerns and don’t break down in the sun. Years ago, mineral sunscreens were famously white and chalky – and therefore less appealing for everyday use. To create sunscreens that are both useable and effective, manufacturers often use nanosize versions of these minerals – materials measured in nanometers, or billionths of a meter – to increase clarity and SPF.
A number of companies sell products advertised as containing non-nano titanium dioxide and zinc oxide. These claims are generally misleading. Although particle sizes vary among manufacturers, nearly all would be considered nanomaterials under a broad definition of the term, including the one proposed in 2011 by the Food and Drug Administration (FDA 2011b).
The use of nanoparticles in cosmetics poses a regulatory challenge, because their properties may vary tremendously, 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.
More research and more specific FDA guidelines are essential to reducing the risk and maximizing the sun protection of mineral sunscreens. Yet even with the existing uncertainties, we believe zinc oxide and titanium dioxide lotions are among the best choices on the American market.
The shape and size of the particles boost sun protection. The smaller particles are, the better the SPF protection and the worse the UVA protection. Manufacturers must strike a balance: Small particles provide greater transparency, but larger particles offer greater UVA protection. The form of zinc oxide most often used in sunscreens is larger and provides greater UVA protection than do the titanium dioxide products that appear clear on skin.
Nanoparticles in sunscreen don’t penetrate the skin. Some studies indicate that nanoparticles in large doses can harm living cells and organs. But a large number of studies have produced no evidence that zinc oxide nanoparticles can cross the skin in significant amounts (SCCS 2012). A real-world study tested penetration of zinc oxide particles of 19 and 110 nanometers on human volunteers who applied sunscreens twice daily for five days (Gulson 2010). Researchers found that less than 0.01 percent of either form of zinc entered the bloodstream.
The study could not determine whether the zinc in the bloodstream was insoluble nanoparticles, so the European regulators concluded it was most likely zinc ions, which would not pose any health risk (SCCS 2012). Other FDA- and EU-sponsored studies concluded that both zinc oxide and titanium dioxide nanoparticles did not penetrate the skin (NanoDerm 2007, Sadrieh 2010). A study by Italian researchers focused on the potential for nanoparticles to cross damaged skin and found no evidence this actually happens (Crosera 2015).
It’s unlikely that nanoparticles in sunscreen cause skin damage when energized by sunlight. Titanium dioxide, and to a lesser extent, zinc oxide, are photocatalysts – when they’re exposed to UV radiation, they can form free radicals that damage surrounding cells. Nanoparticle sizes of these minerals are more affected by UV rays than larger particles are.
Sunscreen manufacturers commonly employ surface coatings that can dramatically reduce the potential for photoactivity, with data suggesting that they reduce UV reactivity by as much as 99 percent (SCCNFP 2000, Pan 2009). In sunscreens, problems may arise if particles aren’t treated with inert coatings, if the coatings aren’t stable, or if manufacturers use forms of zinc oxide or titanium dioxide that aren’t optimized for stability and sun protection. However, tests of living skin from human volunteers and animal tests suggest that these hazards are not a concern for human safety, because the free radicals generated by nanoparticles on skin are quenched by the skin’s own antioxidant protections (Popov 2009, Osmond 2010).
Information from suppliers suggests that U.S. sunscreen formulators generally employ the appropriate forms of zinc oxide and titanium dioxide in their products. Recent studies from other countries indicate that manufacturers don’t always use sunscreen-grade minerals (Barker 2008, Friends of the Earth 2012). Since manufacturers are not required to make this information public, the extent of these problems is difficult to gauge. The EU reviewed 15 types of coated titanium dioxide in sunscreen and concluded manufacturers could use any of them in their products (SCCS 2013b). They specified that other types will also be allowed as long as manufacturers can provide adequate safety data. For zinc oxide sunscreens, both coated and uncoated particles are allowed (SCCS 2014).
Nanoparticles can cause lung damage when inhaled. For many reasons, it is dangerous to inhale nanoparticles. The International Agency for Research on Carcinogens has classified titanium dioxide as a possible carcinogen when it is inhaled in large doses (IARC 2006b). The lungs have difficulty clearing small particles, so the particles may pass from the lungs into the bloodstream. Insoluble nanoparticles that penetrate skin or lung tissue can cause extensive organ damage.
Nanoparticles in lip sunscreens can be swallowed and damage the gastrointestinal tract, although there are no studies to suggest consumers swallow enough zinc oxide or titanium dioxide for this to pose a concern. There is less risk is less if digestion alters the properties of the particles reaching the intestines, but how much less is unclear. We know titanium dioxide has been used for decades as a colorant in commonly eaten foods, including doughnuts and M&Ms, and a recent study found that these particles would be classified as nanoparticles (Weir 2012).
EWG strongly discourages the use of loose powder makeup or spray sunscreens using titanium dioxide or zinc oxide of any particle size. FDA is proposing additional tests for sunscreens in powder or aerosol form to ensure no nanoparticles or small particles are released that could damage the lungs (FDA 2019).
Do current federal sunscreen regulations ensure the safety and effectiveness of sunscreen minerals? No. The U.S. government has not enacted regulations, guidelines or recommendations about particle characteristics that would maximize sun protection and minimize health risks. As a consumer, you’re not likely to find detailed information about nanoparticles on product labels or from companies that make these products.
Nanoscale zinc was approved only recently for use in European sunscreens, except in sprays and powders (EU SCCS 2012). In early 2018, the European safety agency confirmed there was not enough information on nano titanium to allow it to be used in sunscreen sprays (EU SCCS 2018).
FDA sunscreen rules allow any type of titanium dioxide or zinc oxide to be used in sunscreens (FDA 2011a). To ensure the safety and effectiveness of nanominerals 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.
EWG maintains ongoing vigilance in its assessment of sunscreen safety. The available evidence suggests that zinc oxide and titanium dioxide can be safely used in sunscreen lotions applied to healthy skin. The weight of evidence indicates that both zinc oxide and titanium dioxide pose a lower hazard than most other sunscreen ingredients approved for the U.S. market.
EWG’s favorable rating of nanoparticle sunscreens is not an endorsement of nanomaterials in commerce. EWG has urged the FDA to review carefully the safety of nanosize particles in cosmetics products, and to evaluate skin and lung penetration and the potential for greater toxicity to body organs (EWG 2007, 2011). In the case of sunscreens, the potential for human exposure at the consumer level has been carefully studied. Unlike other consumer products with nanomaterials, sunscreens play an important role in cancer prevention.
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 do not harm workers and the environment. More than 50,000 tons of nanoparticle titanium dioxide were produced in 2010 (Future Markets 2011), yet few rules govern the use of protective equipment and other controls to limit inhalation or ingestion during product formulation. A more thorough assessment of worker risks and environmental outcomes is urgently needed.
When zinc oxide and titanium dioxide nanoparticles wash off skin, they enter the environment, with unknown effects. The implications of nanoparticle pollution for the environment have not been sufficiently assessed (Börm 2006). The potential negative environmental effects of nanoscale and conventional zinc and titanium should be carefully studied and weighed against the environmental impact of other UV blockers. Sunscreen ingredients have been shown to damage coral, accumulate in fish and the environment, and disrupt hormones in fish and amphibians (Buser 2006, Danovaro 2008, Giokas 2007, Kunz 2004, Kunz 2006, Weisbrod 2007).
For all sunscreens, including nanoscale zinc and titanium, we urgently need environmental assessments so regulators have the data they need to begin controlling hazards associated with widespread use of these and other chemical ingredients in personal care products.
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