fumed titanium dioxide

Although barium sulfate is almost completely inert, zinc sulfide degrades upon exposure to UV light, leading to darkening of the pigment. The severity of this UV reaction is dependent on a combination of two factors; how much zinc sulfide makes up the pigments formulation, and its total accumulated UV exposure. Depending on these factors the pigment itself can vary in shade over time, ranging from pure white all the way to grey or even black. To suppress this effect, a dopant may be used, such as a small amount of cobalt salts, which would be added to the formulation. This process creates cobalt-doped zinc sulfide. The cobalt salts help to stabilize zinc sulfide so it will not have as severe a reaction to UV exposure.

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On the other hand, the U.S. Food and Drug Administration (FDA) in their Final Administrative Order on Sunscreen Drug Products posted in September 2021 still accepts titanium dioxide up to 25% in the list of Generally Recognized As Safe and Effective (GRASE) in the main document, without further clarification on what kind or size of particles [9]. However, on page 24 (Sunscreen containing nanomaterials) FDA clearly “distinguish nanomaterials from other forms of these ingredients'' (zinc oxide and titanium dioxide) and ask for comments on “any particular nanomaterials that you believe should not be permitted for use in OTC sunscreen products”. To the best of our knowledge, this Agency did not ban the use of nanoparticulate titanium dioxide in any form, even though it is mentioned on page 34 that the anatase form is the more photoactive one, due to the lack of evidence with real sunscreens OTC (over the counter) in vivo. Moreover, other regulations in Latin America (MERCOSUR agreement, 2006) do not state clearly their position on the use of nanoparticulate TiO2NPs [10].

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