A review of critical factors for assessing the dermal absorption of metal oxide nanoparticles from sunscreens applied to humans, and a research strategy to address current deficiencies

Abstract

Metal oxide nanoparticles in sunscreens provide broad-spectrum ultraviolet protection to skin. All studies to assess dermal penetration of nanoparticles have unanimously concluded that the overwhelming majority of nanoparticles remain on the outer surface of the skin. However, possibly due to many different experimental protocols in use, conclusions over the potential penetration to viable skin are mixed. Here, we review several factors that may influence experimental results for dermal penetration including the species studied (human, or animal model), size and coating of the metal oxide nanoparticles, composition of the sunscreen formulation, site of sunscreen application, dose and number of applications, duration of the study, types of biological samples analysed, methods for analysing samples, exposure to UV and skin flexing. Based on this information, we suggest an appropriate research agenda involving international collaboration that maximises the potential for dermal absorption of nanoparticles, and their detection, under normal conditions of sunscreen use by humans. If results from this research agenda indicate no absorption is observed, then concerns over adverse health effects from the dermal absorption of nanoparticles in sunscreens may be allayed.

ZnO nanoparticles and organic chemical UV-filters are equally well tolerated by human immune cells

“…This estimation is based on a standard test sunscreen dose of 2 mg/cm 2 (Gulson et al 2010;, and the respective concentrations of UV-filters in sunscreens coupled with the amount of transdermal penetration (organic UV-filters at the aforementioned 5 -15 wt% of the formulation, with transdermal penetration rates up to 8%; compared with ZnO at 20 wt% of the formulation, with penetration rates of <0.1%). It should J U S T A C C E P T E D also be noted that consumers commonly apply less than the recommended amount of sunscreen (between one-half to one-fifth), so the localised penetration dose would be expected to be lower (Gulson et al 2015;Rodriguez & Maibach 2016). Also, as the transdermal penetration of zinc from particulate UV-filters is at least an order of magnitude less than that of organic UV-filters, their similar bioactivity dose response profiles in human immune cells indicates that NPs have at least an order of magnitude lower potential risk for eliciting these effects in vivo.…”

Biokinetics of nanomaterials: The role of biopersistence

“…Humans encounter NMs from many sources and exposure routes, including ingestion of food (Szakal et al 2014), direct dermal contact through consumer products (Gulson et al 2015; Vance et al 2015), and by inhalation of airborne NMs (Donaldson and Seaton 2012). Environmental exposure on the other hand derives mostly from material aging and waste (Mitrano et al 2015; Neale et al 2013).…”

Cutaneous Permeation and Penetration of Sunscreens: Formulation Strategies and In Vitro Methods

“…Recent advances in nanotechnology have led to the production of nano-sized particles of these metal oxides, whose ability to absorb UV radiation is increased with respect to micronized ones. Unfortunately, TiO 2 and ZnO nanoparticles, in addition to being effective sunblock and eliminating the anaesthetic formation of an opaque film on the skin (due to visible light scattering), seem to possess a photocatalytic activity associated with oxidative stress and genotoxicity [11,12]. Moreover, as frequent application and reapplication after contact to water are recommended, the use of large amount of sunscreens could reflect in possible systemic absorption.…”