SUN CARE


For ZnO, the SCCNFP concluded that more information was needed in order to carry out a full safety evaluation. In response to this, the producers and users of ZnO-based sunscreen ingredients compiled the further data and information requested, and provided the complete data-set as submission II in 2005 to the former SCCP.


Much of the concern around nanoparticles in cosmetics arises from speculation that the particles may penetrate through the skin. This specific aspect has been the subject of many studies, and the evidence shows that insoluble nanoparticles, such as those used in inorganic sunscreens, do not penetrate into or through human skin. Two comprehensive reviews of available literature on the human safety of nano- sized TiO2


and ZnO, covering both skin


penetration/absorption studies and other aspects of safety, have been published in recent years. Nohynek et al concluded in their review:7 “At present, there is no evidence that insoluble ZnO and TiO2 nanoparticles used in sunscreens penetrate into or through


Nanoparticles


human skin or may produce human local or systemic exposure and/or adverse health effects. The evidence of the health benefit of sunscreens clearly outweighs unproven and hypothetical risks… the current weight of evidence suggests that nano-materials such as nano-sized vesicles or TiO2


and


ZnO nanoparticles currently used in cosmetic preparations or sunscreens pose no risk to human skin or human health. Other NP may have properties that warrant a safety evaluation on a case-by-case basis before human use or exposure.”


Subsequent to this review, a number of further skin penetration and other safety studies have been conducted; these were incorporated into a more recent review by Schilling et al,8


which concluded for TiO2 :


“Based on the comprehensive data base and after additional in-depth evaluation, there is no evidence that TiO2 micro- or nanosized particles pose a mutagenic/genotoxic, photo-toxic or photomutagenic/genotoxic risk to humans. On the contrary, there is robust evidence that these substances protect human skin against UV-induced adverse effects,


including DNA damage and skin cancer. The toxicological profile of this material does not give rise to concerns of systemic toxicity since the substance is not absorbed through the skin. Given the long history of use, the hazard-based studies and the absence of dermal penetration, the human risk from exposure to products containing nano-structured TiO2 minimal.”


is considered


For ZnO, Schilling et al concluded: “There is no evidence that ZnO micro-


or nano-structured particles pose a photo- toxic or photo-genotoxic risk to humans. On the contrary, one has to consider that there is robust evidence that this substance protects human skin against UV-induced adverse effects, including DNA damage and skin cancer. Comprehensive in vivo and in vitro dermal penetration studies have been performed. None of these studies yielded any evidence that nanoparticulate ZnO is able to cross the skin barrier in intact as well as compromised skin. Thus, similar to TiO2


, as there is no evidence of exposure to nanoparticulate ZnO, there is no safety concern for human use.”


X Shear forces Aggregates (chemically bonded)


Particle size in final formation Powder


Smallest structure possibly present


Pre-dispersion Formulation


Shear forces Agglomerates (Van der Waals forces)


Agglomerate (1-100 microns)


Aggregates (30-150 nm)


Figure 3: Schematic of aggregation states of inorganic sunscreens.4 132 PERSONAL CARE April 2012


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