Originally Posted by
steaktaco
For the record, sunblock doesn't stop you from tanning, it keeps you from damaging your skin.
I've heard more than once that any SPF rating over 15 is redundant... I guess the way it works, maximum blocking is achieved at 15. However, I'd love if someone has a technical explanation to back this up.
SPF is the number of hours you'd need to be in the sun to equal one hour unprotected. Thus SPF 15 lets 1/15th of the sun through, or roughly 6%. SPF 30 let's 3% or so. SPF 50, 2%. So there's a diminishing return.
Might not be what you're looking for, but it's all I got.