Nanotechnology and Skin Delivery: Infinitely Small or Infinite Possibilities?

By: Johann W. Wiechers, PhD, JW Solutions

Posted: December 19, 2008, from the January 2009 issue of Cosmetics & Toiletries.

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An updated version of the same review was published in June 2008 and reached the same conclusion: "Overall, the current evidence suggests that nano-sized cosmetic or sunscreen ingredients pose no potential risk to human health, whereas their use in sunscreens has large benefits, such as the protection of human skin against skin cancer."³²

A 2006 review concluded that "there is currently little evidence from skin penetration studies that dermal applications of metal oxide nanoparticles used in sunscreens lead to systemic exposure. However, the question has been raised whether the usual testing with healthy, intact skin will be sufficient."⁷

In a review by independent science and technology journalist Trudy Bell, former editor for Scientific American, wrote that size matters, but so do shape and purity. She cautioned that general statements cannot be made presently. She also urged researchers to:⁶

• consider the original sources;
• look for appropriate qualifiers (such as preliminary); 
•  look for issues of scale (Is this substance also toxic in different forms, or in solution?);
• check whether reported exposures were actually to nanomaterials rather than micrometer-sized particles and to individual nanomaterials;
• be cautious about generalizing results from one study to another;
• not assume that experimental results can be extended to actual biological systems or to the environment;
• probe possible other reasons for toxicity; and
• not assume that common-sense macroscopic physics holds at the nanoscale.

She also stated that good R&D takes time. It is therefore not surprising that she does not claim a position on the safety of nanotechnology or nanomaterials. It would be wise to consider her cautionary warnings when reading reports that do make such claims.^{5, 7, 21, 29} Actually, Nohynek et al. already do this when they state that in vitro cytotoxicity, genotoxicity and phenogenotoxicity studies on titanium dioxide or other insoluble nanoparticles reporting uptake by cells, oxidative cell damage, or genotoxicity should be interpreted with caution since such toxicities may be secondary to phagocytosis of mammalian cells exposed to high concentrations of insoluble particles.²¹

This author therefore agrees with their summary conclusion that "Overall, the current weight of evidence suggests that nanomaterials 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, although other nanoparticles may have properties that warrant safety evaluation on a case-by-case basis before human use."