What's the deal with nanoparticles in sunscreen?

Even a sunny winter day warrants sunscreen here in Australia, where skin cancer rates are amongst the highest in the world.

Due to perceived risks, some people are avoiding sunblock that contains mineral nanoparticles, such as zinc oxide. But experts say there is nothing to fear.

Why are nanoparticles in sunscreen?
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There are two ways an active ingredient in sunscreen can protect the skin from harmful UV exposure - either by blocking the rays physically, or by absorbing them chemically.

Generally, a physical sun-blocking substance, such as zinc oxide and titanium dioxide, is more effective, because it reflects and scatters the UV radiation, preventing damage it could do to your skin. Chemical absorbers also prevent the damage, but they typically work by absorbing the radiation and breaking down.

Zinc oxide - the “classic white stuff” - is a widely recognised broad spectrum UV filter for both UVB and UVA rays.

And when these mineral powders are in nanoparticle form, they come on clear, without leaving much of a white residue on the skin. Nanoparticles are typically defined to be between 1 and 100 nanometres in size - for comparison, one human hair is around 75,000 nanometres in diameter. 

Are nanoparticles dangerous?
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Risks to human health always depend on the specific substance in question, not just its particle size.

“A one-size-fits-all approach to evaluating the potential risks and benefits of nanotechnology for human health is not possible because it is both impractical and would be misguided,” writes nanotoxicologist and RMIT Associate Professor Paul Wright in an article published this week in the Medical Journal of Australia.

So, potential hazards have to be assessed for each material individually. If something contains nanoparticles, that alone doesn’t actually tell you anything about its impact on your health.

"Nanotechnology as a term came into public knowledge only around the mid-nineties, so a lot of people's perception was that it's new and scary," says Professor David Lewis, a nanoscience researcher from Flinders University.

"Any phone that we're using is a product of nanotechnology, it's very common in everyday lives, but people get twitchy about things they don't understand. That's not entirely unreasonable,"  he adds.

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Are sunscreen nanoparticles dangerous, then?
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Evidence shows they are safe and effective.

In 2008 a report came out stating that coated steel roofs were bleached by nanoparticles in sunscreen residue left on said roofs by workers. This sparked concern with some environmental activist groups, however scientific research since then has shown these nano-sized ingredients are safe to use on the skin.

"Research has shown that the nanoparticles do not penetrate the skin readily,” says Wright.

"Exposure of the human skin is very different to exposure of the roofing material, which is under the hot Australian sun for months on end, with a lot of UV exposure,” he explains. “In the case of human skin, we're shedding millions of skin cells a day.”

Compared to levels of zinc as a necessary trace element in our blood, what gets absorbed from sunscreen is an exceedingly small amount.

“We have also investigated the other major concern raised by some public groups that metal oxide nanoparticles in sunscreens are a risk to us because they produce free radicals,” says Wright.

His studies show that both zinc oxide and the rutile crystalline form of titanium dioxide nanoparticles actually reduce overall free radical generation. Furthermore, zinc in its nano form is hypoallergenic and least likely of all sunblocks to irritate your skin, making it an even better choice.

Meanwhile, exposure to harmful UV in sunrays is definitely proven to be harmful to your health.

"People are being scared of using protective measures because of a perceived risk by some that the nanoparticles in sunscreen are more of a risk," says Wright. "They're simply not - the benefit far outweighs the risk!"

The only proven danger of zinc oxide particles is if you inhale too much of them, but that's equally bad for you either in nano form or larger particle size. Just to be safe, it's also best not to ingest any sunscreen, although a small amount on the lips is considered okay.

Is this a nanoparticle conspiracy?
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ANU Law Professor Thomas Faunce does not agree with toxicologists who have done this research, and believes that nanoparticles should be clearly labelled on sunscreen formulations available on the market, so that people can make informed choices.

According to Faunce, the nanoparticle industry “stands to make a lot of money” out of these products. However, zinc oxide is primarily used in various industrial applications such as rubber manufacturing and ceramics.

"Industry use of zinc oxide is a far bigger part of their market," says Wright, pointing out that for manufacturers of these nanoparticles sunscreen comprises a small piece of the income pie.

“In the case of sunscreen, I welcome nanoparticle labelling too, because I think that nano zinc oxide is the superior product. There's no conspiracy," says Wright.

"[For lay people] it makes a field difficult to research if there are people who are prepared to talk outside their area," he adds.

Activist groups sometimes cite regulations in other countries as 'proof' that zinc oxide must be bad for you, but the EU actually approved zinc oxide in both nano and non-nano form as a UV filter late last year.

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What about alternatives?
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Apart from mineral sunscreens, the other widely available type are formulations containing chemical filters made out of organic compounds, such as oxybenzone, octocrylene, homosalate and several others.

But when it comes to health risk, these filters can actually be more problematic that nanoparticles - they are far more likely to cause skin irritation or trigger allergic reactions, and studies have shown they are much more readily absorbed by human skin than mineral nanoparticles. So, if what you're worried about are chemicals entering your body through the skin, physical sunblock with nanoparticles is once more a better option.

The bottom line is that if something has 'nano' in the name, that doesn't automatically make it a hazard. Your best strategy is always to follow the scientific evidence, and slop on some sunscreen, even when it's cloudy. 

Read more on nanoparticles in sunscreen
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MJA: Potential risks and benefits of nanotechnology: perceptions of risk in sunscreens

Choice: Is your sunscreen doing more harm than good?

Environmental Working Group: Nanoparticles in sunscreens

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