Safety of sunscreens containing nanoparticles of zinc oxide or titanium dioxide
February 2006
Australia has the highest rate of skin cancer in the world. The use of sunscreen is an important way to reduce the risk of developing skin cancer and premature skin ageing.
Zinc oxide and titanium dioxide have been used as sunscreens for many years. They are particularly valuable because of their ability to filter UVA as well as UVB light, giving broader protection than other sunscreening agents. Of the 1200 sunscreens authorised by the TGA for supply in Australia (December 2005), 228 contain zinc oxide, 363 contain titanium dioxide and 73 contain both.
One disadvantage of zinc oxide and titanium dioxide is that they are visible, giving the skin a white colour. This effect can be reduced by decreasing the particle size of the material. When used in 'nanoparticle' form (less than 100 nanometers, or one millionth of a millimeter), they can't be seen on the skin but still retain the sunscreening properties of the coarser material.
At the present time around 70% of sunscreens with titanium dioxide and 30% of sunscreens with zinc oxide have these materials in nanoparticle form. Titanium dioxide has been used in this way since at least 1990 and zinc oxide since 1999. There is no evidence that sunscreens containing these materials pose any risk to the people using them.
A theoretical concern has been raised that if zinc oxide or titanium dioxide in nanoparticle form are absorbed into skin cells they could possibly interact with sunlight to increase the risk of damage to these cells. However, initial studies are limited in number and have proved inconclusive.
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 Medicines Evaluation Committee endorsed this conclusion at its meeting on 2 February 2006.
The Therapeutic Goods Administration is monitoring the emerging scientific literature in this area and working cooperatively with international agencies to monitor these issues and ensure that appropriate action is undertaken if any risks are identified.
A review of the scientific literature on the safety of nanoparticulate titanium dioxide or zinc oxide in sunscreens (pdf,133kb)