Tag Archives: 2013

Anatase and rutile titanium dioxide and nanosunscreens

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The American Chemical Society (ACS) features some research into nanoscreens and the anatase form of titanium dioxide in a Sept. 25, 2013 news release,,

Using a particular type of titanium dioxide — a common ingredient in cosmetics, food products, toothpaste and sunscreen — could reduce the potential health risks associated with the widely used compound. The report on the substance, produced by the millions of tons every year for the global market, appears in the ACS journal Chemical Research in Toxicology.
Francesco Turci and colleagues explain that titanium dioxide (TiO2) is generally considered a safe ingredient in commercially available skin products because it doesn’t penetrate healthy skin. But there’s a catch. Research has shown that TiO2 can cause potentially toxic effects when exposed to ultraviolet light, which is in the sun’s rays and is the same kind of light that the compound is supposed to offer protection against. To design a safer TiO2 for human use, the researchers set out to test different forms of the compound, each with its own architecture.

They tested titanium dioxide powders on pig skin (which often substitutes for human skin in these kinds of tests) with indoor lighting, which has very little ultraviolet light in it. They discovered that one of the two most commonly used crystalline forms of TiO2, called rutile, easily washes off and has little effect on skin. Anatase, the other commonly used form, however, was difficult to wash off and damaged the outermost layer of skin — even in low ultraviolet light. It appears to do so via “free radicals,” which are associated with skin aging. “The present findings strongly encourage the use of the less reactive, negatively charged rutile to produce safer TiO2-based cosmetic and pharmaceutical products,” the researchers conclude.

It should be noted that the researchers used pig skin, i.e., the skin was not on a pig and, therefore, not part of a living organism with its various biological systems coming into play. As well, the testing was done indoors not under direct sunlight which is the condition under which most of us use sunscreen. This research points to problems  with using anatase nanoscale titanium dioxide in sunscreens but it doesn’t provide unequivocal proof.

The Danish Environmental Protection Agency report (this Oct. 3, 2013 posting of mine) on the state of the art of research into nanomateial dermal absorption does refer to research in this area, although it does not include Turci’s work (Note: The numbers n the excerpted text are reference numbers for the bibliography)),

When looking at bulk composition and the level of dermal penetration noted in studies using a specific material type, there appears to be very little pattern between bulk composition and penetration depth. Taking for example TiO2 as one of the most widely studied nanoparticles, we see reports of penetration no further than the SC [subcutaneous skin layer] 78, 86, 91 but also several studies suggesting deeper penetration (basal cell layer) and even penetration into the dermis 63, 84 although this is often reported as being a very small fraction/infrequent. Another compositional issue in relation to nanoparticles and in particular TiO2 is the crystalline structure. TiO2 is often used in either its anatase or rutile form or as mixture of both. Within the literature, there are studies using both the anatase form 86, 94, the rutile form 91, 114 or a mixture 84, 114 although we were unable to find any studies which appear to systematically evaluate the role of crystal form in TiO2 absorption into the skin. [emphasis mine] (p. 44 of this report: Dermal Absorption of Nanomaterials Part of the ”Better control of nano” initiative 2012 – 2015 Environmental Project No. 1504, 2013).

For those who would like to read Turci’s research for themselves,

Crystalline Phase Modulates the Potency of Nanometric TiO2 to Adhere to and Perturb the Stratum Corneum of Porcine Skin under Indoor Light by Francesco Turci, Elena Peira, Ingrid Corazzari, Ivana Fenoglio, Michele Trotta, and Bice Fubini. Chem. Res. Toxicol., Article ASAP DOI: 10.1021/tx400285j Publication Date (Web): September 12, 2013
Copyright © 2013 American Chemical Society

This research is behind a paywall.

Danish evaluate research on absorption of nanomaterials through the skin

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An Oct. 3, 2013 news item on Azonano announces a report produced by the Danish Environmental Protection Agency on the state of research into dermal absorption of nanomaterials  (Note: A link has been removed),

 A new report published by the Danish Environmental Protection Agency (EPA) provides a comprehensive evaluation of the knowledge base regarding the dermal absorption of nanomaterials.

The report is the final output of the project “Dermal absorption of Nanomaterials”, which forms part of the “Better Control of Nano” initiative 2012 – 2015 conducted by the Danish EPA with the aim of further clarifying possible risks to consumers and the environment from nanomaterials.

The overall objectives of the project – which was led by the Institute of Occupational Medicine (IOM) working with COWI A/S – were to:  i) gather and evaluate the existing knowledge concerning the dermal absorption of nanomaterials, ii) assess the need to generate new knowledge, and iii) develop recommendations for the most suitable skin models, measurement methods and relevant candidate nanomaterials for future experimental testing.

The report: Dermal Absorption of Nanomaterials Part of the ”Better control of nano” initiative 2012 – 2015 Environmental Project No. 1504, 2013 gives a good description of skin and a good technical overview of the literature and the state of the research which, for the interested reader, could supply the basis for a better understanding of how to read research papers on this topic.  The report does not offer consumer information about nano sunscreens, etc.

Here’ are some of the conclusions from the Executive Summary,

One of the key challenges in assessing the literature on the physicochemical properties influencing dermal penetration/absorption of nanomaterials is that it is difficult to draw conclusions due to either: i) limitations in the reporting of physicochemical data, and/or, ii) the alteration of multiple experimental parameters in a non-systematic way. The issue of a lack of information on nanoparticle physicochemical properties is common, yet the most challenging aspect is the alteration of multiple experimental parameters whereby multiple characteristics such as shape, charge, coating, size can all be changed. This means that little meaningful comparison of results can be made within a single experimental study, let alone between studies.

Despite such challenges, some key conclusions can be drawn. [emphasis mine] Whilst there are many conflicting results, on balance the literature seems to suggest that absorption of particles in the nano-range through the skin is possible although occurs to a very low degree and that the level of penetration, depending on chemistry and experimental conditions, may be greater than for larger particles. The role of size is considered a critical component of dermal absorption but this in itself does not seem to guarantee absorption or lack of as other properties can also influence dermal absorption markedly. In addition, particle size is not necessarily a constant parameter as agglomeration of particles can occur over time and also in relation to experimental conditions (e.g. presence of surfactants within particle vehicle formulation). However, whilst this issue of agglomeration has been suggested as being important (as well as an important experimental variable), agglomeration state is often not reported within studies.