How does sunblock work?

freckleface · Joined: 09 Mar 2009 Posts: 15

I've read the sunscreen/sunblock info on the Smart Skin Care site, but I'm left with a few nagging questions.

If physical sunscreens rely mostly on their ability to reflect or deflect the UVA/UVB rays, wouldn't the sunblock have to be visible on the skin's surface? With the micronization of zinc oxide and titanium dioxide, the idea is for the sunblock to sink into the skin. If zinc and titanium dioxide are soaked up by the skin and no longer sitting on the skin's surface, how are these ingredients then able to reflect rays if they are essentially sitting below the skin's surface? Aren't the rays are first hitting the skin, then the sunblock?

Along the same lines, if a physical sunblock relies on its reflective properties, what happens to the effectiveness of the block when flesh colored tints are added to lessen their white appearance? Isn't that lessening or even canceling the benefits of sunblock?

orangehrzn · Joined: 23 Feb 2005 Posts: 1005

micronized sunscreens stop reflecting the visible light but keep reflecting the UV light which is not visible

micronized sunscreens form a reflective film on skin surface but you don't see it since they don't scatter visible light. they don't 'sink in the skin'.

freckleface · Joined: 09 Mar 2009 Posts: 15

I'm not sure I totally understand, because you used the term sunscreen, and I'm only talking about physical sunblocks. Did you mean to say sunblock? So, if sunblocks form a reflective film on the skin surface, wouldn't it be important not to interfere with that film?

I read about people applying sunblock, and then putting powder, foundation, etc. on top of the sunblock in order to mask the white-ishness.

Whether micronized or non-micronized, does adding flesh colored tint (essentially adding makeup foundation) obscure the ability of the sunblock to reflect the UV light?

orangehrzn · Joined: 23 Feb 2005 Posts: 1005

The tint and the sunscreen reflect different part of the spectrum.

The tint is visible so it reflects visible wavelengths but passes through the UV. If that wasn't the case, one could use the tint as sunscreen.

The micronized sunscreen doesn't reflect visible wavelength or does it very little, that is why it is invisible. It strongly reflects the UV part of spectrum, that is why it's effective as sunscreen.

freckleface · Joined: 09 Mar 2009 Posts: 15

So I can put powder or foundation on the top of a physical sunblock without hindering the ability of the sunblock to block UVA/UVB?

I could also mix tinted foundation WITH a physical sunblock?

orangehrzn · Joined: 23 Feb 2005 Posts: 1005

yes, putting foundation on top is better, mixing it with the sunblock might interfere with the homogeneous distribution of the micronized sunscreen particles but is not likely

lilypotter · Joined: 25 Jun 2009 Posts: 9

I agree with orangehrzn, sunscreen helps a lot.