Last week, the Victoria branch of the Australian Education Union (AEU) passed a resolution recommending that “workplaces use only nanoparticle-free sunscreen” and that sunscreens used by members on children are selected from those “highlighted in the Safe Sunshine Guide produced by Friends of the Earth” as being nano-free.  The AEU also resolved to provide the Friends of the Earth Safe Sunscreen Guide and Recommendations to all workplaces their members are associated with.  Given what is currently known about sunscreens – nano and otherwise, I can’t help wonder whether this is an ill-advised move.

The debate over the safety or otherwise of nanoparticle-containing sunscreens has been going on for over a decade now.  Prompted by early concerns over possible penetration through the skin and into the body of the nanosized titanium dioxide and/or zinc oxide particles used in these products – and potential adverse impacts that might result – there has been a wealth of research into whether these small particles can actually get through the skin when applied in a sunscreen.  And the overall conclusion is that they cannot.  There have been a small number of studies that demonstrate that, under specific conditions, some types of nanoparticle might penetrate through the upper layers of the skin.  But the overwhelming majority of studies have failed to find either plausible evidence for significant penetration, or plausible evidence for adverse health impacts – a body of evidence that led the Environmental Working Group to make an about-face from questioning the use of nanoparticle-containing sunscreens to endorsing them in 2010.

So why is the AEU now advising against their use?  And why are they advocating selecting sunscreens based on a document that does not provide evidence-based advice on efficacy or safety – and may end up leading to decisions that increase the risk of sun-related skin damage in children (more on this below)? (Update 5/25/11 – see notes below)

In part, the answer lies in the uncertainty inherent in proving anything safe.  It’s not too difficult to show that something is unlikely to be harmful, or is probably safe.  But proving something is absolutely safe under all conditions of use is simply not possible – there is always some room for doubt.  This is why decisions on health risks are typically based on plausible risk and weight of evidence – evaluating the most reasonable and defensible interpretation of the data, and not basing decisions on speculation and fantasy.

With the use of nanoparticles in sunscreens, the weight of evidence is that they are safe and effective – and may be safer and more effective than a number of non-nanoparticle alternatives as they work by coating the skin rather than being absorbed into it.  That said, it’s always prudent to check whether anything has been missed with a relatively new technology like this, and so research is ongoing just to make doubly sure that the nanoparticles currently being used stay on top of the skin, and that manufacturers are using the safest possible types of nanoparticles.

But there is another reason I suspect why the ASU have released this advice, and that is due to a study using human volunteers that was published last year.

In this study by Brian Gulson and colleagues, sunscreens were formulated with zinc oxide particles made from a stable isotope of zinc that doesn’t occur in great abundance naturally: Zn-68. Using Zn-68 as a tracer, they were able to tell whether zinc from the applied sunscreen entered the bodies of the volunteers, and ended up in their blood and urine.

The detected presence of Zn-68 in the urine and blood of volunteers was used by Friends of the Earth Australia to renew their recommendations against using nanoparticle-containing sunscreens until more is known about their safety in.  And given the ASU’s reliance on the Friends of the Earth document, it seems to have influenced their decision to recommend not using nanoparticle-containing sunscreens.

But what does the Gulson study actually conclude?  In a nutshell, the researchers showed that:

• Small amounts of zinc from sunscreens containing any form of zinc oxide particles tested found their way into the blood and urine of volunteers.
• The amounts of zinc entering the body over the five day study were miniscule – around one thousandth of the concentration of zinc already in the volunteers’ bloodstream, and around one thousandth of the amount of zinc recommended in a person’s daily diet.
• Women in the test generally showed higher uptakes of zinc than men.
• Zinc levels in blood associated with the sunscreen peaked some days after applications ended, suggesting the zinc or zinc oxide was stored somewhere in or on the body and slowly released.
• For men, zinc uptake from sunscreens was independent of particle size.  For women, zinc uptake was greater from the sunscreens containing smaller particles.

So did the particles go through the skin?  The study only showed that the zinc passed through the skin, and did not provide any evidence of particle penetration.  Two possible explanations for this are that the particles penetrated and entered the bloodstream, or that the applied particles dissolved, and that it was dissolved zinc that was penetrating into the body.

Out of the two possibilities, there is minimal evidence for particle penetration being a plausible mechanism. On the other hand, zinc oxide is sparingly soluble, and under the acid-conditions of the outer layers of the skin the particles would have readily released zinc ions.  The weight of evidence to date therefore strongly supports dissolution of the particles and subsequent dermal penetration of dissolved zinc.  This is supported by the similarity in uptake seen in men of zinc for two different sizes of zinc oxide particles.

In other words, this study provides neither compelling evidence that nanoparticles in sunscreens can pass through the skin, or that they can lead to worrying internal exposure to harmful materials.  It did indicate on the other hand that any sunscreen containing zinc oxide will lead to zinc entering the body via the skin – including sunscreens that rely on large zinc oxide particles.

And this is where it is worth returning to the Friends of the Earth recommendations.

The Friends of the Earth Safe Sunscreen Guide recommends:

Use a nano-free zinc-based SPF 30+ broad spectrum sunscreen in conjunction with protective clothing, a broad-brimmed hat, sunglasses and shade to stay sun safe.

It goes on to list sunscreens that are “nano and chemical free”, “may use nano” and “use nano” (based on information from manufacturers and assumptions from Friends of the Earth).

Passing over the fact that Friends of the Earth are advocating the use of sunscreens that demonstrate the same behavior – zinc penetration through the skin into the body – as the sunscreens they recommend people don’t use, it’s hard to understand how this document provides an authoritative and evidence-based guide for the use of sunscreens on school children – as suggested by AEU.

For a start, this is a document that is specifically concerned with nanoparticle-containing sunscreens, and is not aimed at providing advice on selecting sunscreens as a whole based on their safety and efficacy.  It is advocating a specific course of action, and is not a tool for taking informed action. And in this respect alone it is a questionable document to be distributing to school workers. But it gets worse.

The sunscreens listed in the document are listed solely with respect to their nanoparticle content.  There is no – let me repeat that no – information on how effective these sunscreens are at protecting against UVA and UVB, and what the specific safety issues associated with their use are (update 5/25/11 – see notes below).  What is more, the top tier products – those that appear to be most strongly endendorsed by Friends of the Earth – also claim to be “free of UV-absorbing chemicals”.  In other words, this is a document that appears to be endorsing the use of products that do not necessarily protect against ultraviolet light. (Update 5/25/11 – see notes below).

To be fair to Friends of the Earth – and this is not a critique of their document so much as a questioning of its use as authoritative guidance – they do recommend the use of sunscreens providing substantial UV protection that are (presumably) based on large zinc oxide particles.  But if school workers were to base their choice of what to slather onto kids on the list of products, rather than the one sentence top level recommendation, they could well be applying sunscreens that do not protect against skin damage.

And this is my greatest concern here – by advocating the use of the Friends of the Earth document, AEU could actually be endangering the health of children in the care of their members. (Update 5/25/11 – see notes below)

Of course, there are important issues to grapple with here – including how appropriate sunscreens should be selected for use on children, irrespective of the technology being used.  But surely these selections should be based on the best possible evidence that is focused on what is most appropriate for the children, and not on an action campaign by an advocacy group, no matter how well intentioned.

Update, 5/25/11:  As clarified by Georgia Miller of Friends of the Earth Australia in the comments below, the sunscreens listed in the top tier of the Friends of the Earth document are all – as far as I can tell – marketed as offering SPF 30 + protection.  This is something that I do not think is explicitly clear in the document, and the heading of “nano and chemical-free”, clarified with “products also free of UV-absorbing chemicals” raises an obvious question to the naive reader over whether these products do indeed offer significant protection.  I also continue to have serious reservations over the use of a document designed to steer people away from nanoparticle-containing sunscreens as authoritative advice on sunscreen protection for children, given it’s lack of independent testing and evaluation of all significant factors that might affect choice in a given situation.  Nevertheless, given the protection ratings of the recommended sunscreens, I have on reflection retracted the statements made in regard to the protection offered above.