The Environmental Working Group group has released a report on sunscreen protection and most got sketchy ratings or thumbs way down. Now, with that in mind, I don't trust these guys and their findings but they do supply references.
Why don't I trust them? Because they have singled out their favorite brands which says to me they have a brand bias rather than ingredient bias. Now, to give them the benefit of the doubt, it also may suggest that they are going under the assumption that each sunblock company has their own SPF factory but none of them do.
These"brands" simply buy 100's of 55-gallon barrels of the goop from an original equipment manufacturer, squish it into brightly, colored, plastic, bottles and then sell it for 10xs what they paid for it. (That is the business plan. same goes for vitamins, supplements and shampoo. Shampoo only cost a 2-cents in real life.)
In my opinion, If I put on a cheap sunscreen, I don't burn and burning causes inflamation and inflamation is associated with cancer. Do they prevent skin cancer? I don't know but I want to go outside anyway and not burn so I not going to play favorites until the FDA comes out with an opinion.
Here is a snippet:
1. There’s no consensus on whether sunscreens prevent skin cancer.
"... The Food and Drug Administration’s 2007 draft sunscreen safety regulations say: “FDA is not aware of data demonstrating that sunscreen use alone helps prevent skin cancer” (FDA 2007). The International Agency for Research on Cancer agrees. IARC recommends clothing, hats and shade as primary barriers to UV radiation and writes that “sunscreens should not be the first choice for skin cancer prevention and should not be used as the sole agent for protection against the sun” ..."