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Nanoparticles and sunscreen safety
(Nanowerk Spotlight) The use of nanoparticles in sunscreens is one of the most common uses of nanotechnology in consumer products. Well over 300 sunscreens on the market today contain zinc oxide or titanium oxide nanoparticles.
Skin cancer is the most common cancer in the world today, and the number of cases worldwide is growing each year. The single most important risk factor for basal and squamous cell carcinoma (the two most common forms of skin cancer) is prolonged sun exposure, so it’s not surprising that the manufacture of sunscreen is a US$400 million dollar industry (despite the fact that no one has ever determined that sunscreens actually prevent skin cancer.)
With that kind of money at stake, the sunscreen industry has become highly competitive. Short of proving that sunscreens actually prevent skin cancer, there are a few areas of sunscreen development that could stand improvement. One of the most common complaints about sunscreens is that they don’t rub into the skin very easily. When applied, their two most common ingredients – zinc oxide (ZnO) and titanium dioxide (TiO2) – give the skin a white tinge. If manufacturers could develop a less visible sunscreen, people would definitely buy it.
That’s where nanotechnology comes in. The use of nanoparticles in sunscreens is one of the most common uses of nanotechnology in consumer products. By replacing traditional forms of ZnO and TiO2 with nanoparticles of these substances, manufacturers can reduce the visibility of the cream.
Ironically, while consumers apply sunscreen to stay healthy, the use of nanoparticles in sunscreen may prove riskier than sun exposure itself. Recent studies show ZnO and TiO2 can induce the formation of free radicals when exposed to light – and this may damage cells. Preliminary investigation into the ability of ZnO and TiO2 nanoparticles to penetrate healthy skin has revealed conflicting results. Most studies have found that these nanoparticles do not reach the living cells. However, a few have suggested they do ("Toxic Potential of Materials at the Nanolevel"); and broken skin is ineffective as barrier for particles as large as 7,000 nm.
In Australia, where skin cancer rates are extremely high, the manufacture and use of nanotech sunscreens is increasing. Of the 1,200 sunscreens authorized by the Therapeutic Goods Administration (Australia’s version of the FDA), 228 contain ZnO, 363 contain TiO2 and 73 contain both. According to the TGA, about 70 percent of sunscreens with TiO2 and 30 percent of sunscreens with ZnO contain these substances in nanoparticle form.
In January 2006 the TGA conducted a review of the scientific literature in relation to the use of nanoparticulate zinc oxide and titanium dioxide in sunscreens. The review concluded that:
"There is evidence from isolated cell experiments that zinc oxide and titanium dioxide can induce free radical formation in the presence of light and that this may damage these cells (photo-mutagenicity with zinc oxide). However, this 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 (stratum corneum) of the skin."
The Australian Medicines Evaluation Committee endorsed this conclusion.
Australians are not the only consumers of these products. In the U.S., with the cosmetics industry free from labeling requirements, it’s difficult to say how many nano-sunscreens are on the market. However, according to Friends of the Earth, one the most vocal advocates of increased safety testing, there are dozens (Friends of the Earth published a report in May 2006 that takes a very critical look at nanomaterials in cosmetics: "Nanomaterials, Sunscreens and Cosmetics; Small Ingredients, Big Risks"). The FDA has not disclosed any relevant figures.
Like any other concern about nanotechnology and safety, there is not enough information available to determine the safety of these products. Until there is, sun worshippers will have to decide for themselves whether transparent sunscreen is worth the risk.
By Cathy Garber and Michael Berger, Copyright Nanowerk LLC

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