Titanium dioxide is a photocatalyst: https://en.wikipedia.org/wiki/Titanium_dioxide https://en.wikipedia.org/wiki/Titanium_dioxide That article mentions that

Titanium dioxide is a photocatalyst: https://en.wikipedia.org/wiki/Titanium_dioxide https://en.wikipedia.org/wiki/Titanium_dioxide That article mentions that when it is coated with other things it does not penetrate the skin. However "self cleaning" paints that cause the disintegration of organic matter that lands on the paint also use titanium dioxide: https://www.sciencedirect.com/science/article/abs/pii/S0959652615015504 https://www.sciencedirect.com/science/article/abs/pii/S09596... So what does this self-cleaning ability do to the skin? Remove the outer layer? Kill the skin microbiome? Maybe the same encapsulation prevents this happening? It is hard to believe some particles would not escape encapsulation. I don't know of any other catalysts in general considered safe to eat.