Danielle, totally an great question! They do break down. They do, however help to offset the damage. At least they don’t break down as fast as they would if you didn’t have sunscreen. This is one reason why you should wear an antioxidant serum underneath your sunscreen. To put it in a nutshell; antioxidant in sunscreen simply aren’t enough!

Danielle: that’s a good point. Antioxidants degrade when exposed to sunlight, not sure if that happens immediately but very rapidly, yes. Since sunscreens are supposed to be reapplied frequently anyway I wouldn’t worry too much about it. Nanoparticles can’t penetrate the skin so even if antioxidants weren’t added I doubt they would generate free radicals.

Anastasia: lol, I had to google that, I’m not a Stargate fan unlike my mom. She has never missed an episode. But they sound pretty nasty.
I know, it sounds silly to me but since nanoparticles can’t penetrate skin, I don’t think that would be a problem. I’m more concerned about chemical sunscreens that are said to generate free radicals too and that’s why I tend to avoid them. I stick to Zinc Oxide and Titanium Dioxide as they are the best sunscreen ingredients available at the moment and I don’t mind the white cast either. Kinda matches my skin anyway.

Jojoba: I agree with you. Although topical application is supposed to be safe, and is definitely safer that not wearing sunscreen or using one that doesn’t offer broad spectrum protection, these particles haven’t been studied much and some concern about their safety (esp regarding inhalation) remain. Based on current research, I wouldn’t avoid sunscreens with nanoparticles, but I’d still I’d rather stick to physical sunscreen that don’t contain them as they are a better option.

prettybeautiful: that is a very common misconception. But actually these particles can’t penetrate skin (most ingredients used in beauty products can’t, doesn’t matter what marketing says) and in any case, you wouldn’t want them too. In order to protect the skin from the sun rays, these ingredients have to remain on the surface. I don’t mind the white cast either, being properly protected is more important.

If they can create free radicals, it seems a wee bit daft to me, considering that the sun is one of the primary causes of free radicals and thus one of the reasons why we use sunscreen.

Personally, I wouldn’t mind having a white cast. I’m already milk-colour, I welcome pale.