May 26, 2011

Protection: Chemical vs. Mineral Sunscreens

Since my discovery about the evils of my chemical sunscreen, I set about researching mineral sunscreens.  With such beautiful weather and summer just beginning, now seems like perfect time to share! Please forgive me, I'm going to get a little science-y in this post.

Chemical sunscreens contain some ingredients we want to avoid, so that limits us to mineral sunscreens (at least until ivy leaf particles are available in sunscreen, said to be four times more effective than mineral sunscreens. Get on it scientists!). Besides their unsavory ingredients, I found out that chemical sunscreens actually are less effective in the UVA range than mineral sunscreens. This took me by surprise.

Figure showing the protection offered by chemical vs. titanium dioxide vs. zinc oxide sunscreens. The more red, the better the coverage. Left: Neutrogena Dry Touch Sunblock SPF 100+ (chemical), Middle: California Baby Sunscreen SPF 30+ (titanium dioxide), Right: Elemental Herbs Sunscreen SPF 20 (zinc oxide). Taken from the Cosmetics Database.

The UV absorbence figure shows the amount of protection each sunscreen provides at different wavelengths. The higher the red bars, the more coverage. In the UV absorbence figure you can see that the UVB protection of chemical sunscreens is stellar (left most plot). However, chemical sunscreens are far less effective in the UVA range. In fact, Neutrogena falls to near zero protection at the far end of the UVA spectrum.

If you compare Neutrogena to the middle plot, which shows California Baby sunscreen (which uses 18% titanium dioxide), the UVB protection in a mineral sunscreen is actually even BETTER than the chemical sunscreen. The UVA protection of California Baby is much better than the Neutrogena as well. Overall, you can see it covers more of the UV range.

Now if you look at the Elemental Herbs sunscreen (rightmost plot), which uses 25% zinc oxide, you can see that the UVA protection of zinc is even better than the titanium. However, the UVB protection is better with titanium. Nevertheless, what is most clear from this plot, is that the least protection is provided by the Neutrogena SPF 100 sunscreen. Ironic, huh? Thought that big number 100 might mean something. Not so much.

This means that a different amount of protection is achieved from the different active ingredients in sunscreen. UVB is best covered by titanium dioxide, and UVA is best covered by zinc oxide. And the higher the percentage of each, the more coverage you get.

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