Zinc Oxide and photoactivity with active ingredient from other skincare cosmetic product
I have been reading a lot about active ingredients in sunscreen and noticed that only TiO2 and ZnO are considered as GRASE category 1 in the FDA proposed ruling. When I looked into studies that have been done on these ingredients, it looks like they both exhibit photocatalytic when they are exposed to light. Although many products on the market are contained coated versions of the metal oxide to decrease their photocatalytic activity of them. Some product still uses the uncoated version of the metal oxide in the sunscreen. I am curious if anyone knows the potential risk of using sunscreen containing uncoated metal oxide and potential photocatalytic that can occur when such sunscreen is being used with other skincare/cosmetic products. I am especially interested in Zinc Oxide since I didn’t find much information on coated Zinc Oxide. I found this very interesting since I know the individual product needs to pass a certain test to established its photostability, but since we are using so many different products daily, will the photocatalytic activity also degrade/reacts with other ingredients from different product? Any insight would be helpful.