The Therapeutic Goods Administration (TGA) has banned an ad for Invisible Zinc, a sunscreen that advertises itself as "nanoparticle free", on the grounds that it is likely to cause fear and distress in consumers. "TGA remains concerned that promotion of goods as 'nano free' may imply that therapeutic goods that contain nanoparticles are unsafe when there is no evidence that this is the case," a TGA spokesperson was quoted in the SMH. The decision looks like a case of shooting the messenger. Fear and distress are not always irrational responses. There may not be much evidence nanoparticles are unsafe, but the evidence for safety is far from conclusive. Nevertheless, the TGA seems determined to make it difficult for anyone who would prefer to err on the side of caution. Nanoscience is the science of the very small. Nanoparticles are particles 1-100 nanometres across. Nanoparticles are one of the hottest buzz areas in science, (literally as I typed that line the radio announced Australia was getting its first centre for nano-medicine). Their high surface area to volume offers potential for everything from the delivery of drugs with fewer side effects to cheap, flexible solar-power producing films. The field is so exciting that areas of research that are not really nanoscience have taken to rebadging themselves in the hope an association will attract funding or attention. All of which means it would be tragic if the image of nanoscience was destroyed by the premature approval of unsafe nanoproducts. One of the fascinating things about nanoparticles is the way the behaviour of materials change with the particle size. Gold nanoparticles, for example, aren’t gold. Their colour ranges from red to yellow depending on particle size. The colour changes are harmless, but that doesn’t mean differences in particle behaviour will always be so benign. Nanoparticles in sunscreen form the front line of this debate. Sunscreens are one of the first applications of nanoparticles, and certainly the first most consumers have experienced. Titanium dioxide and zinc oxide have been used in sunscreens for many years with particles well above nano-scale. However, by reducing the particle size the sunscreens become invisible; a significant attraction when marketing to the aesthetically minded. Our bodies are unused to dealing with particles of this size, leading to concerns they may be harmful. In addition to the general concern that something novel may have hidden dangers, nanoparticles can induce the formation of free radicals, whose reactivity triggers cell damage, increasing the risk of cancer and degenerative diseases. Calls for a single specialist regulatory body to assess the safety of nanoparticles have gone unheeded. However, the TGA released a paper in May concluding nanoparticles in sunscreen are safe. They argue "[free radicals] would only be of concern in people using sunscreens if the zinc oxide and titanium dioxide penetrated into viable skin cells. The weight of current evidence is that they remain on the surface of the skin and in the outer dead layer." Associate Professor Thomas Faunce, of ANU Medical School, noted to the ABC however, that cuts or skin abrasions may bring nanoparticles into contact with functioning cells. Moreover, intriguing work at the University of Bristol has raised the possibility that nanoparticles can affect DNA even without making contact. The nanoparticle concentration in the Bristol research was vastly higher than in sunscreen, and any application to living tissue is speculative, but it suggests consumers may have legitimate concerns. Dr Amanda Barnard, of CSIRO’s Virtual Nanoscience Laboratory, is a leading expert in the way nanoparticles change when exposed to varying conditions. Her work modelling the way environments alter nanoparticles has won her a string of awards including the Malcolm McIntosh Prize for Physical Science. She says she ventured into studying sunscreens because so many people asked about their safety. Her work is tentatively positive for nanoparticles. Barnard found potentially dangerous concentrations did not occur for SPF ratings below 50. SPFs above 30 are illegal in Australia, albeit for other reasons. So far so good. However, Barnard notes her work was only on titanium dioxide. If anyone has done equivalent research on zinc oxide she’s not aware of it. "I did the research on titanium dioxide because I happened to have worked on it years ago and I already had data," Barnard says. She also adds her work only looked at free radical formation. Other potential ways in which nanoparticles might be harmful were not considered. Dr Cathy Foley, head of CSIRO’s division of materials science and engineering (and also president of the Federation of Australian Scientific and Technological Societies), has stated that incomplete work in a different CSIRO division has so far aroused no concerns about nanoparticle safety. So on a balance of probabilities the research suggests sunscreens containing nanoparticles are safe. Certainly, even under a worst-case scenario nanoparticles pose far less of a risk than excessive sunlight. Offered the choice between sunburn or nanoparticle-containing sunscreen anyone who gets burnt isn’t thinking rationally. Many consumers, however, may prefer to adopt a precautionary approach. Why use nano-sunscreens when alternatives are available? Particularly when research that might yield a greater degree of confidence has yet to be done? Yet the TGA has not forced manufacturers to report the presence of nanoparticles in their products. Friends of the Earth have issued pamphlets listing which brands contain nanoparticles, but how many people, even among those who are concerned, will remember to take bring a copy with them to the supermarket? One might expect where there is doubt about the safety of a product the TGA would err on the side of caution. Even if confident enough to allow nanoparticles in sunscreen on the market, one might expect they would insist on manufacturers informing consumers so they could make their own assessment. To prevent competitors from alerting consumers to the existence of nano-particles in their rivals suggests a level of certainty of a higher order still -- one the current research hardly seems to warrant.