The Environmental Working Group (EWG) – a US-based non-profit organization committed to using public information to protect public health and the environment – has just released what is probably the most comprehensive evaluation to date of the safety and effectiveness of using titanium dioxide and zinc oxide nanoparticles in sunscreens.  And their conclusion?

On balance, EWG researchers found that zinc and titanium-based formulations are among the safest, most effective sunscreens on the market based on available evidence.

In other words, not only are zinc oxide and titanium oxide nanoparticle-based sunscreens OK, but they are safer and more effective than many non nanotechnology-enabled sunscreens.

What makes this statement so startling is that EWG is not known for treating regulators and industry with kid gloves.  This is how the organization describes it’s way of working:

Our research brings to light unsettling facts that you have a right to know. It shames and shakes up polluters and their lobbyists. It rattles politicians and shapes policy. It persuades bureaucracies to rethink science and strengthen regulation.

EWG is about as far as you can get from a bunch of industry lackeys.  Yet here they are endorsing one of the more controversial products of nanotechnology…

For the past few years, the safety of using nanometer-scale particles in sunscreens has been hotly debated.  As manufacturers have  turned increasingly to nanoscale mineral UV-blocking agents in place of more conventional chemicals, speculative questions over whether the nanometer-scale particles of titanium dioxide or zinc oxide being used could penetrate through the skin and harm people have been asked.  In the absence of conclusive safety-focused research, some groups have suggested that nanoparticle-based sunscreens should be avoided in favor of more conventional products, where there we have a clearer idea of the possible risks.  In 2007, Friends of the Earth published “A consumer guide for avoiding nano-sunscreens,” kicking off with:

Sun worshippers beware.  While slathering up with sunscreens to block dangerous ultra-violet (UV) rays you may be exposing yourself to a new danger.  Sunscreen manufacturers are adding nanoparticles to sunscreens to make sun-blocking ingredients like titanium dioxide and zinc oxide rub on clear instead of white. These nanoparticles are being added without appropriate labeling or reliable safety information.

Even EWG admit that their researchers were skeptical about the use of nanoparticles in sunscreens, and thought the organization would end up advising against their use.

Over the past few years, there has been a growing body of published data addressing the effectiveness and safety of nanoparticle-containing sunscreens.  EWG researchers ploughed through nearly 400 studies in their quest to assess what the upsides and downsides might be for consumers.  Importantly, they also compared these data to what is known about conventional UV-blocking agents like octinoxate and oxybenzone.

The result is a comprehensive, robust analysis that wouldn’t be out of place in a peer reviewed scientific journal.  The conclusions are highly relevant to consumers concerned over which sunscreens to use, companies paranoid over how they present their products, and governments wondering how to regulate nanotech-enabled sunscreens.  The report states:

Our study shows that consumers who use sunscreens without zinc and titanium are likely exposed to more UV radiation and greater numbers of hazardous ingredients than consumers relying on zinc and titanium products for sun protection. We found that consumers using sunscreens without zinc and titanium would be exposed to an average of 20% more UVA radiation — with increased risks for UVA-induced skin damage, premature aging, wrinkling, and UV-induced immune system damage — than consumers using zinc- and titanium-based products. Sunscreens without zinc or titanium contain an average of 4 times as many high hazard ingredients known or strongly suspected to cause cancer or birth defects, to disrupt human reproduction or damage the growing brain of a child. They also contain more toxins on average in every major category of health harm considered: cancer (10% more), birth defects and reproductive harm (40% more), neurotoxins (20% more), endocrine system disruptors (70% more), and chemicals that can damage the immune system (70% more) (EWG 2007).

We also reviewed 16 peer-reviewed studies on skin absorption, nearly all showing no absorption of small-scale zinc and titanium sunscreen ingredients through healthy skin. In a 2007 assessment the European Union found no evidence of nano-scale particles absorbing through pig skin, healthy human skin, or the skin of patients suffering from skin disorders (NanoDerm 2007). Overall, we found few available studies on the absorption of nano-scale ingredients through damaged skin, but nearly all other sunscreen chemicals approved for use in the U.S. also lack these studies.

In contrast to zinc and titanium, the common sunscreens octinoxate and oxybenzone absorb into healthy skin — in large amounts according to some studies. These 2 sunscreens can cause allergic reactions, can lead to hormone-driven uterine damage, and can act like estrogen in the body, raising potential concerns for breast cancer.

On balance, EWG researchers found that zinc and titanium-based formulations are among the safest, most effective sunscreens on the market based on available evidence. The easy way out of the nano debate would be to steer people clear of zinc and titanium sunscreens with a call for more data. In the process such a position would implicitly recommend sunscreen ingredients that don’t work, that break down soon after they are applied, that offer only marginal UVA protection, or that absorb through the skin.

EWG acknowledge that more research is still needed, alongside effective oversight, to ensure that nanotech-enabled sunscreens are as safe as possible.  But the key message is that the current balance of evidence supports their use as a safe and effective alternative to more conventional sunscreens.

I cannot emphasize enough how important this report is.  The analysis is credible and the conclusions drawn are supported by the current state of the science.  It should reduce consumer concerns over using nanoparticle-based sunscreens, and allow them to make informed decisions that will result in better UV protection.  It should also encourage companies developing and selling nanoparticle-enabled sunscreens to stop obscuring  the fact – either by avoiding any mention of nanoparticles, hiding behind silly euphamisms alike “micronized,” or coming up with elaborate explanations of why their product doesn’t actually contain any nanoparticles.  These are good products using an effective technology, and companies shouldn’t be shy to let people know!

That said, there is still work to be done.  There are gaps in our understanding of how titanium dioxide and zinc oxide nanoparticles behave on the skin and in the environment that it would be good to fill.  Approaches to testing these materials need to be fully evaluated. And regulators need to clarify the rules concerning the safe use of these materials.

Given what still isn’t known, EWG cautioned against the use of nanoparticles in cosmetics at the moment, where they are not being used to protect the wearer’s health.  But when it comes to protecting the skin the organization was clear – nanoparticle-based sunscreens.

End Notes

The full EWG report on “Nanotechnology & Sunscreens” can be read here.

This is part of a larger review of sunscreens, which is accessible here.

Something not covered in the EWG report is nanoparticle agglomeration.  Some companies have claimed that, while the basic size of titanium dioxide and zinc oxide particles they use is in the range of 1 – 100 nm, they form much larger agglomerates in the products and should therefore not be considered “nanoparticles.”  While this may be the case for some products, it isn’t universal, and there are still questions over whether large agglomerates could disaggregate when applied to the skin.  However, given the EWG’s findings and conclusions, the question of agglomeration doesn’t seem to be that important from a consumer’s perspective.

One concern over the use of titanium dioxide and zinc oxide nanoparticles in sunscreens is that these materials are photoactive, and could become more harmful when exposed to sunlight.  As the EWG report notes, most manufaturers treat the nanoparticles to supress their photoactivity.  Howere, there is some evidence that products containing photoactive particles could still be entering the market.   Whether this is important from a health perspective is unknown, although the indications are that it probably isn’t a significant concern when the particle-containing sunscreens are appolied to healthy skin.

Andrew Maynard