The Guardian has this week published an article that puts nanotechnology sunscreen safety into the spotlight.

“Wear sunscreen”, advised film director Baz Luhrmann in his 1999 hit song Everybody’s Free (To Wear Sunscreen), claiming that “the long-term benefits of sunscreen have been proved by scientists”. But with the inevitable march of technology, and recent forays into the field of nanotechnology, is all sunscreen safe?

The Australian Education Union (AEU) seems to think not: in May 2011 it recommended that all education workspaces refrain from using sunscreens that contain nanoparticles. “With early indications that some nano sunscreens may present hazards, so many unanswered questions about skin penetration, and a lack of effective regulation, there is no need for schools to take a risk,” says Georgia Miller, from Friends of the Earth Australia. The AEU council resolution, based on information from Friends of The Earth’s Safe Sunshine guide, cites “growing evidence that nanomaterials present unique health and safety hazards”.

The perceived problem lies with zinc oxide and titanium dioxide. Both have long been added to sunscreens to make them more effective at reflecting away the sun’s harmful ultraviolet radiation, but in recent years nanoparticle versions have appeared on the shelves. The smaller particles make the cream clear, rather than leaving unattractive white marks on the skin, meaning people are more likely to apply it. There is also some evidence to suggest that nano sunscreens are more effective.

But Miller and others believe not enough is known about the potential dangers of this move to miniaturisation. A 2010 study, led by Brian Gulson, at Macquarie University, Australia, found very small amounts of zinc in the blood and urine of human volunteers after use of both nano and non-nano sunscreens. Higher levels were found after using the nano sunscreens. Some fear that once inside the body, this higher level of smaller particles could potentially cause harm. The effect on more sensitive types of skin, such as those broken by cuts or by conditions such as eczema, along with the effect on children’s skin, is also a concern for those like Miller who argue more research is needed.

However, the weight of current scientific evidence suggests nano sunscreens do not present a danger. “The nanoparticles would only be toxic if they reach viable [living] cells,” says Richard Moore, scientific director of the Institute of Nanotechnology. “The balance of evidence suggests [they] do not.” A 2009 report by the Australian government’s Therapeutic Goods Administration reviewed the available research and found that 15 out of 16 studies, almost all of which were carried out in Europe, indicated titanium dioxide and zinc oxide were unable to reach viable cells. Miller argues, however, that these studies are “overwhelmingly short-term and do not consider the role of skin condition”.

Nano sunscreen sceptics also point toward the fact that titanium dioxide is photoactive – it can react with sunlight to create chemicals known as free radicals. The structure of these atoms or molecules renders them highly chemically reactive, meaning they can attack the sunscreen itself, breaking it down and rendering it less effective. They could also damage the body’s cells if they manage to pass through the skin barrier.

Aware of this potential danger, nano sunscreen manufacturers have come up with a solution: adding a small amount of the metal manganese dramatically reduces free radical production by dissipating the energy absorbed from the UV light before it has a chance to create them. Optisol, manufactured by UK company Oxonica, is an example of a UV absorber.

But some doubts persist. A 2008 Australian study, by Barker and Branch at BlueScope Steel Research, found small sections of steel sheet roofing, pre-painted with titanium dioxide, degrading much faster than normal. In just 18 months, some areas showed signs of wear usually only found after 15 years. The culprit turned out to be sunscreen, accidentally spilt by workers or introduced to the steel through their hands or boots.

In subsequent tests, five out of six sunscreens containing nanoparticles were shown to degrade the steel; none of the four non-nano sunscreens tested did any damage. Further analysis indicated free radicals produced in the presence of sunlight were to blame. Despite being designed to greatly reduce the production of free radicals, the nano sunscreens significantly accelerated the degradation of the roofing.

However, there is no clear evidence these free radicals pass through the skin. “People need to weigh up the known and substantial risk of sun damage, against the speculated and unsubstantiated risk of nanoparticle damage,” says Andrew Maynard of the University of Michigan Risk Science Center.

Colipa, the European Cosmetics Association, highlights that all cosmetics brought on to the market must undergo expert safety assessments under 1976 European Union legislation. Miller warns, however, that “where active ingredients have been assessed by regulators, and approved for use in larger particle form, there is no requirement for the new nano-forms to face assessment”.

In an attempt to allay these fears, from 2013 EU regulation will require all cosmetics using nanoparticles to state so on their labels. But despite research into safety, and the attempts at regulation, the public still feel they aren’t given enough information, according to a report by Matter, an emerging technologies thinktank. “People want to choose whether or not to use these products. But in order to make that choice you need to have all the information. That’s where things currently reach an impasse,” says Matter’s director, Hilary Sutcliffe.

Perhaps if the publicly available information was as clear as the cream itself, everybody would be free to wear sunscreen after weighing up the risks for themselves.