Size Matters! Issues and Challenges with Nanoparticulate UV Filters.

Preparations containing pigments have been used since ancient times to protect against negative effects of solar radiation. Since the 1950s, sunscreen products containing micronized TiO2 and ZnO have been marketed. These products were soon regarded as cosmetically unattrac-tive due to their property of remaining as a white paste on the skin, a result of particle sizes. In order to eliminate these unfavourable properties, particle size distribution was lowered into a range below 100 nm, a size threshold for decreasing the particle's optical property to reflect visible light. After 2000, new nanoparticulate organic filters were developed. Effects of both the inorganic and organic nanoparticulate substances - alone or in combination - with non-particulate UV filters were well documented and had shown great effectiveness. At the time, nanotechnology fuelled great hope in the progress of science and technology, including the health sector and cosmetics industry. Instead, influenced by images from the science fiction literature of self-replicating nanorobots destroying all living matter or health and environmental disasters caused by asbestos, fear of this new unknown amongst the general population has hindered acceptance and progress of nano-enabled products. Consumers have started to suspect that the particles permeate through skin, are absorbed by the blood and are distributed throughout the body, causing disease. Not least because of public pressure, cosmetics - which include sunscreen products - became the first product segment in which appropriately manufactured substances were subject to stringent rules. Despite advanced regulation and rigorous approval procedures for nanoparticulate UV filters, widespread reservations remain. Possible reasons could be a lack of knowledge of current legislation and unclear ideas about nature and behaviour of nanoparticles. Against this background, we discuss the nature and behaviour of nanoparticulate UV filters within finished products, on the skin and potentially in the skin, and the regulatory framework that ensures that nanoparticulate UV filters and the sunscreen products containing them are safe to use.