First let's look at the two different kinds of active ingredients in sunscreens. There are the chemical ingredients like oxybenzone, adminobenzoic acid, and avobenzone (to name a few) and there are the physical barrier ingredients titanium dioxide and zinc.
Here's how they work:
Chemical ingredients absorb the energy of UV rays before it affects your skin
Physical barriers reflect or scatter UV rays before they hit your skin
Right off the bat when researching this and coming upon this info I thought to myself--So the chemical ingredients rubbed into my skin absorb the UV rays?
What are some of the negative effects of the chemical sunscreen ingredients?
While there are many negative effects associated with the chemical ingredients used in sunscreen, it seems the most common include the generation of free radicals in the body and affect on estrogen in the body. Looking at the common sunscreen ingredient Benzophenone, it may come as a surprise that it is actually used in industrial processes as a free radical generator to initiate chemical reactions. It also happens to be one of the biggest culprits in regards to free radicals in the body as a result of using sunscreen that contains it. And since up to 35% of the sunscreen you rub into your skin can end up in your bloodstream, it doesn't seem like something you want to slather all over your body. Also, the fact that some chemicals in sunscreen have an estrogen-like affect on the body can increase the risk of cancer and cause a number of other fairly severe issues.
Comparing chemical ingredients side by side with physical barriers:
So maybe you think the information floating around about the chemical in sunscreen and how awful they are is a lot of hype. I think everyone needs to read and weigh the information themselves and perhaps while I'd rather err on the side of caution, you feel that something that's been in use for so many decades can't possibly be that bad of a culprit. All of that aside, let's look at a super basic, super objective comparison of the two when it comes to protection from the sun. After all, that's why we smear it all over our bodies anyway, right?
You are probably already aware that there is a broad UV spectrum broken down to UVA and UVB more or less. Now you may not believe it, but chemical sunscreen ingredients only cover portions of the spectrum which is why you usually see 3 or 4 active ingredients on your sunscreen. Adding these chemical ingredients together causes the sunscreen to have a bit more protection against different portions of the spectrum. At the same time, titanium dioxide as well as zinc provide broad spectrum UVA AND UVB protection.
Here's an awesome chart I can across that shows the protection offered by both chemicals and physical barriers: (Scroll to bottom of page) http://www.dermatology.ucsf.edu/skincancer/general/prevention/sunscreen.aspx