title: 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.
authors.affiliation: Faculty of Science, Graduate School of the Environment, Macquarie University, North Ryde, Sydney, NSW, 2109, Australia. brian.gulson@mq.edu.au.|CSIRO Earth Science and Resource Engineering, North Ryde, NSW, 2113, Australia. brian.gulson@mq.edu.au.
authors.forename: Brian
authors.identifier: http://orcid.org/0000-0002-4741-0926
authors.initials: B
authors.lastname: Gulson
authors.affiliation: CSIRO Animal, Food and Health Sciences, North Ryde, NSW, 2113, Australia.
authors.forename: Maxine J
authors.initials: MJ
authors.lastname: McCall
authors.affiliation: Risk Science Centre and Department of Health Management and Policy, School of Public Health, University of Michigan, Ann Arbor, MI, 48109-2029, USA.
authors.forename: Diana M
authors.initials: DM
authors.lastname: Bowman
authors.affiliation: Departamento de Engenharia e Ciências Nucleares e Instituto de Bioengenharia e Biociências, Instituto Superior Técnico, Universidade de Lisboa, EN 10, 26, 2695-066, Bobadela LRS, Portugal.
authors.forename: Teresa
authors.initials: T
authors.lastname: Pinheiro
mesh_terms: D000279:Administration, Cutaneous; D000818:Animals; D006801:Humans; D007391:International Cooperation; D053768:Metal Nanoparticles / Q000008:administration & dosage*; D010087:Oxides / Q000737:chemistry; D010316:Particle Size; D012107:Research Design; D012867:Skin / Q000378:metabolism; D012869:Skin Absorption; D013473:Sunscreening Agents / Q000008:administration & dosage* / Q000493:pharmacokinetics
chemical_list: D010087:Oxides; D013473:Sunscreening Agents
keywords: Nanoparticles; Skin; Sunscreen; Titanium dioxide; Zinc oxide