Issues relating to the use of Micro and Nanoparticle Zinc Oxide in Personal Care Products based on Skin Penetration Studies

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Nanoparticles of ZnO and TiO2 are increasingly being used as pigments and UV absorbers in personal care products (e.g. sunscreens), coatings and paints, predominantly because their UV absorbance efficiency and transparency to visible light increases with decreasing particle size. There is community and scientific recognition that current safety and efficacy data on these compounds obtained from material with much larger particle size is inadequate (and possibly irrelevant) for extrapolation to their nanoparticulate counterparts especially in relation to the stated applications. Receiving particular attention is the use of nanoparticles in personal care products with the main concern being their phototoxicology. Scant attention has been placed on the effect of particle size on the fate of these materials after application including their penetration into and possibly through the skin.
The purpose of the current study was to assess and compare the in vivo penetration behaviour of nano- and micro- sized ZnO particulates into human stratum corneum (SC) after topical sunscreen application. To determine the penetration of nano-sized ZnO into the SC and hence its distribution on or in the uppermost layers of the SC, a method of sequential removal of layers of stratum corneum by adhesive tapes known as tape stripping was adopted.
The study revealed that a large proportion of the ZnO applied remained on the surface or at least in the uppermost layers of the SC and the mean percentage of recovery after 18 tape strips varied between approximately 70 and 100%. The differences in the recovery between nano and micro ZnO at both t0 and t2hrs were insignificant (p>0.05) suggesting the reduced particle size of ZnO alone did not enhance its ability to penetrate further into the SC.
Although the study suggested that there was little apparent difference in the penetration behaviour of these particles into the stratum corneum, it raised several potentially significant issues relating to the efficacy of using nanosized additives in personal care applications. These will be discussed.

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Journal: TechConnect Briefs
Volume: 1, Technical Proceedings of the 2006 NSTI Nanotechnology Conference and Trade Show, Volume 1
Published: May 7, 2006
Pages: 541 - 544
Industry sectors: Advanced Materials & Manufacturing | Medical & Biotech
Topic: Environmental Health & Safety of Nanomaterials
ISBN: 0-9767985-6-5