Organic sunscreens have been the mainstay of commercially available products for years. It does not mean that they are naturally occurring and, in fact, they are not. Organic sunscreens are relatively complex molecules that are to some degree absorbed into the skin. PABA became so well known because a significant number of people turned out to be allergic to it. It is probably the one most associated with adverse reactions.
Physical sunscreens are actually microscopic solid pieces of sunscreen.
Zinc oxide and Titanium dioxide are the two that are commonly used. Most people associate zinc oxide with the white thick paste lifeguards used to use. Fortunately, things have changed and you can now get physical sunscreens that are transparent. Zinc oxide, for example, is now manufactured so that the particles are so small that you can not see them. The sunscreen manufacturers now use Z-COTE and other microfine powders as ingredients in their sunscreens.