Sunscreen Confusion

Violent Pink · 08-12-2008, 11:57 AM #1 (**permalink**)

So, having recently heard about the release of free radicals into the skin when chemical sunscreen degrades in UV light (if you don't reapply), I started doing a little bit of research.
If you're confused, some easy resources:
Sunscreen - Wikipedia, the free encyclopedia
Sunscreen controversy - Wikipedia, the free encyclopedia
As far as I understand it, there are two main types of sunscreen: chemical ("organic chemical") and mineral ("inorganic particulates"). If you read the wikipedia article, I'm not going to delve into the third type, as it is not available in the US, but if you have knowledge/experience with this type, please share anyway.
The scientific research is not complete (is research in any field ever?) but here there still seems to be a fair bit of controversy. I've been reading different things, and I was curious as to what sort of insight, links, et al. other specktrettes could provide.
Some bullet point questions I have:

Layering SPF products. I have read that when you do this, you average your protection (for example: 15 spf foundation + 30 spf sunblock provide about 22 spf worth of protection). This resource states that the highest SPF wins. However, I've also read that a study showed zinc and titanium to degrade avobenzone, (though the time period was over a week and in aqueous solution, so who knows how relevant this is to actual use!). Does this mean wearing mineral sunscreen renders any chemical sunscreen I might be wearing irrelevant?

Reapplication. How often should you do this? Different resources have drastically different answers. The prevailing knowledge seems that you should reapply every couple hours. However, Wikipedia states, "Upon exposure to UV light, most of the ingredients (with the notable exception of Avobenzone) do not undergo significant chemical change, allowing these ingredients to retain the UV-absorbing potency without significant photodegradation." That would make reapplication seem redundant-- which is fine with me. Reapplying sunscreen on my face over makeup is not really an option for me day-to-day, so I'd really like to use something stable enough to last a normal day of sun exposure (in situations where I'm outside all day, theme parks/beach etc, I'll reapply often, however).

Mineral Sunscreen seems like a great alternative. It's not as irritating, presumably because your skin does not absorb it. However, with my use, it gives the face an odd bluish pallor, and I am already one pale mf. I can't even imagine the problems this would cause for WOC! Can this be prevented/altered without basically painting over it with makeup?

What sort of sunscreen do you use? Please state the product, whether it's a chemical or mineral barrier, and if you think it's relevant, the UV-blocking agents present. Do you reapply, and if so, how often? What are your experiences with this product?

Sario · 08-14-2008, 03:39 PM #2 (**permalink**)

True, we have chemical and physical here. Chemical works by absorbing the UV radiation and translating it into heat energy so it doesn't damage your skin. Physical blocks scatter the radiation particles/waves so they don't reach your skin to begin with. (in a nutshell of course)
Since chemical sunscreens must be absorbed by the skin to work fully you should apply about a half hour before exposure to sun. Physical blocks just sit on the surface, hence why they tend to give a whitish cast to skin so they don't need to be applied that far in advance of exposure. Chemical sunscreens are also more prone to degradation on the skin, so they should be reapplied every two hours or so, while with physical blocks you can get away with every three or four hours.

When you layer protection, you don't add or average, you still get the same protection of the individual products - spf 20 cream under spf 15 powder still just gives spf 20, although if you use more than one product you're less likely to miss spots. I don't like to rely on just powders like mineral makeup for spf because you would have to apply a great deal more than you use for makeup to get the spf protection on the label, it's very misleading. It's something like seventeen times more than the average application would be needed to get the labeled SPF. Avobenzone on its own can react with things in mineral makeup to degrade it, although in most cases now avobenzone is stabilized with other chemicals (like with parsol/avo-triplex/other brand names) If you're wearing MMU though, I'd just probably stick with a physical sunblock underneath and not worry about it.

Personally right now I'm using Shiseido's spf 55/pa+++ lotion in the blue bottle, it has both chemical and physical sunscreens in it so it protects against the full spectrum of UVB/UVA1/UVA2 (uvc is filtered out by the ozone layer). I reapply this one about twice a day. I love this one because it doesn't leave my skin shiny and greasy and it's a pretty significant protection factor. I also really like neutrogena's ultra sheer dry touch spf 85, which is a chemical sunscreen so must be reapplied every two hours. It leaves me a bit oilier than the shiseido though.

And on reapplication - for the body, use a full ounce, about a shotglass full. For just the face, use half a teaspoon, about 2 mL, and apply all the way down the neck.

Hope this helps, I had a really big talk with my derm recently about sunscreen because I had a tough time sorting out the piles of research, but it really boils down to find a broad spectrum sunscreen you'll wear and like, apply early and apply often!

Violent Pink · 08-14-2008, 11:04 PM #3 (**permalink**)

How do you reapply without jacking up your makeup? I mean, I suppose protecting my skin is far more important, but is it possible for me to have my cake and eat it too?

Sario · 08-18-2008, 10:50 AM #4 (**permalink**)

I'm naturally a greasy kid so usually by the time I need to reapply (lunch-ish and when I get home if I'm doing the physical block thing) my makeup is a mess anyway. Living in a subtropical sauna probably doesn't help either. I usually just use a wipe and do a quick once over from scratch, I've gotten all ninja stealth master at doing it pretty quickly =)

hollyca · 08-18-2008, 11:10 AM #5 (**permalink**)

They make sunscreen with powders now. Sephora is selling it. I haven't tried it yet nor can I remember the name but it's in a white tube. That way you can reapply and not mess up your makeup!

athena123 · 09-02-2008, 06:59 PM #6 (**permalink**)

Because of the possibility that chemical sunscreens will break down and create more free radicals, I stick to mineral (physical sunscreens only). The active ingredient is either Titanium Dioxide or Zinc Oxide or a combination of both.

For body, I've found Blue Lizard Australian sunscreen to be fairly effective. Have worn it to the beach several times this summer, reapplied it whenever I climbed out of the water and didn't experience a burn. Because it's physical barrier method, you don't have to apply it 20 minutes ahead of time.

For facial sun screen, I've been using NIA24 for the past year. It also contains niaciamide, a form of vitamin B that promotes skin barrier repair, it's 100% mineral and also serves as a primer.

I'm still on the fence about the chemical ingredients like Mexoryl -- just a little uncomfortable with how they interact with UV rays and would rather just take the approach of deflection than worry about what happens when the UVA and UVB rays penetrate beneath the surface of my skin.