… a rash of recent studies has shown that labels on several popular brands are not only misleading and confusing but, in some cases, completely false.
After testing 786 name-brand sunscreens to gauge their stated UVA protection, potential health hazards and stability in sunlight, the Environmental Working Group determined that only 17% of them provide good protection and minimal risks.
… Be sure to check out the full article (linked below) for a complete list of common misperceptions and suggestions on how to ensure you’re adequately protected.

Are Most Sunscreens Really that Helpful? (TreeHugger)
And why are products of such dubious value, so poorly regulated, so expensive?