Nanomaterials or nanoparticles are generally described as one to 100 nanometers (nm) in size. “Nano” means a billionth of a meter. Many natural materials are nano-scale such as fine sand and ocean spray, also the scales of butterfly wings and the crystalline proteins in spider silks. In the context of UV filters “nano” is big! Organic sunscreens, for example Ethylhexyl Methoxycinnamate, have a molecular weight of less than 300 Daltons which would correlate to a size of less than 1 nm. Inorganic UV filters are much larger than this, so “nano” UV filters are comparatively big.
Croda’s Solaveil titanium dioxide (TiO2) and zinc oxide (ZnO) UV filters are designed in a range of particle sizes, whether they are described as nanoparticles or not depends on the definition that is used and the test method that is used
In the global Personal Care Industry there is no common definition of a nanoparticle. In Europe there are three different definitions that are most commonly referred to.
There is no official test method described in any of the definitions. Centrifuge methods and light scattering methods are the most common ones used in our industry. Currently we use the X-Ray Disc Centrifuge (XRDC) method as we find centrifuge methods give the most reliable and reproducible results for inorganic UV filters as they are most sensitive to particles smaller than 100nm, but we can provide particle size measurements using Dynamic Light Scattering (DLS), if required. Statements about the particle size and safety of all of Croda’s mineral powders and dispersions are available on request from your sales representative.
Croda's Solaveil range contains a large array of particle sizes to provide different levels of protection depending on your needs. As the classification of nanomaterials depends on the definition and the test method that is used, Croda provides statements for customers on a request basis. Please contact your sales representative for further information.
Yes, it doesn’t matter what definition or test is applied, the most important aspect is nanomaterial safety. All regulatory bodies globally approve TiO2 and ZnO as UV filters at levels up to 25% active. The past controversy around nanoparticles was linked to fears that they pass the skin barrier. More recently TiO2 concerns are linked to the fact that International Agency for Research on Cancer (IARC) has classified it as a potential carcinogen by inhalation (see “Using Titanium Dioxide, Reclassification in Europe")for more information on occupational exposure to inhalable particles). However, the vast majority of sunscreen are applied dermally and not impacted by the potential for inhalation.
Extensive safety reviews have been conducted by the US Food & Drug Administration (FDA) and the EU Scientific Committee for Consumer Safety (SCCS). These reviews have concluded that whatever their size (nanomaterial or not) they do not penetrate the skin.
Research has been conducted by Croda in collaboration with other leading suppliers and end-use formulators on the human safety of nano TiO2 and ZnO and is available here.
Titanium dioxide used for cosmetic applications is coated which mitigates any photocatalytic action and cosmetic grade titanium dioxide has never been found to cause phototoxic effects. Croda’s Solaveil TiO2 range has been tested for photoactivity and is below the threshold set by the SCCS opinion. Zinc oxide on the other hand has no photocatalytic activity which is the reason that it can be used in its uncoated form.
Titanium dioxide exists in 3 main crystal forms: rutile, anatase and brookite. Rutile (used by Croda) has a higher refractive index than anatase and is therefore more effective as a UV attenuator and is also more photostable than anatase. The brookite form is of little interest commercially and is not used at all in UV-attenuating grades.
No. Croda does not use soluble Aluminum. Croda uses Aluminum oxide (alumina) and Aluminum stearate which is chemically different to soluble Aluminum, and does not give rise to soluble Aluminum as it is chemically bound to the surface. Aluminum salts are accused of playing a role in the development of breast cancer and Alzheimer's disease. Although many international expert groups have concluded that there is no current evidence to support this link, they are currently under review by the SCCS.
However the aluminum species used in the coating of TiO2 UV filters is chemically different to the soluble aluminum salts of concern. Aluminum species used as coatings (Aluminum oxide (alumina) and Aluminum stearate) are insoluble compounds which cannot give rise to any soluble aluminum species.
Coatings are chemically bound to the surface
Extensive testing has proved that coated TiO2 does not penetrate through the skin
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